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MG Midget and Sprite Technical - Engine Breather and HUUGGGGEEEEE blue clouds !!

1965 AHS with 1275cc Marina engine

Having driven the car most of the summer with the timing cover breather just venting into a rubber hose that went up from the timing cover vent can, then a gentle upturned 'U' shape then tie wrapped to the radiator bottom hose (old style vertical radiator) and vented on to the floor, I drove the car from Tamworth to Brighouse at about 70mph (about 2 hours), then back again a day later to find a glistening mist of oil from the dipstick all over the engine - the engine lost something like 2 litres of oil so I decided to 'fix' it.

So I, removed the timing cover, cleaned the gauze and refitted the cover, then cleaned and checked a PCV (the flat topped disc thing on the inlet manifold) from a 1968 MGB -( the moss part numbers are the same for the B and Sprite) and fitted that, connected the hose from the timing cover to the PCV and since then the car has embarrassed me with the oil clouds.

Disconnected the pipe from the timing cover to PCV and it is dripping with oil - so the oil separator in the timing cover appears not to be separating but it's clean - what have I missed ?


I've had a look thru some of the archive but not found anything useful yet.
Malc Gilliver

lol - not found anything useful?? this must be one of the most discussed topics on here - eh Lawrence??

Just to add a bit of controversy ( is that possible??)
the gauze may actually be intended as a flame trap, not an oil separator at all.....
Chris at Octarine Services

Second only to front wheel bearings!

Surely if you are losing that amount of oil without the pcv sucking it out there must be an issue with the engine. Compression test?

GraemeW (Kent!)

have you used a non-vented oil filler cap and have you followed the cleaning and reassembly instructions for the valve as per Driver's Handbook - it also tells you a quick simple test you can do on the breather (if it's fitted in standard way)

it's certainly true this subject comes up a lot but usually when the breather system is non-standard for the year/model

and as usual I suggest posting a/some good photos of your arrangement as that *may* highlight something

ETA: do you have any vacuum devises fitted
Nigel Atkins


I found lots of stuff, but most related to mod'd engines.


It is the PCV doing the sucking - but why ?


The rocker box has a bent 7/16 - 1/2" tube sticking out the top, I haven't read the 'drivers handbook', I just took the PCV apart, dunked it in paraffin, then cleaned it with gunk and rinsed with water, then checked the diaphragm looked ok and re-assembled.

I think this car should have a breather as standard, the PO thought otherwise

No other vacuum devices

Malc Gilliver

'Ere we go again. Luveryl jubbly. lol. I agree Chris, I'm not entrirely convinced that the wire gauze is an oil separator. I think the empty breather canister does that, -- as long as it isn't filled with oil. In my opinion, the gauze is to trap small solids to prevent them being drawn into the inlet.

Actually nigel, it comes up a lot even if the correct breather system is employed.

Malc. The short answer is, --- nobody knows the answer. Except that you've added a mushroom PCV to a marina engine. They were never fitted with them were they? So I suppose it's possible that it's being overwhelmed by too much suction from the manifold, or that it's just not working properly. Didn't the marina employ the Y piece into twin pipes, into the carbs, that Spridgets used? -- Less suction at the carbs than at the manifold.

You say there was a mist of oil being expelled from the dip stick. Even when blowing clouds of oil myself, I've never had that. So it does sound like you have a fair bit of sump pressure.

"so the oil separator in the timing cover appears not to be separating but it's clean - what have I missed ?"

To be dripping with oil, the pipe must have been full, as must have been the separator canister. The 64 thousand dollar questions are.

Why does the canister fill with oil?
Why doesn't the oil drain back fast enough to prevent the canister being filled with oil?

What's the history of your engine?
Lawrence Slater

Here's how a Marina 1300 engine breather system was connected up.

No pipe in the rocker cover. Breather canister into the carb. Vented oil filler cap.

Assuming you have twin carbs, get yourself a y piece and connect the breather as shown, but also connected to the 2nd carb. Try that and see what occurs.

Lawrence Slater

the rocker cover may not be the right one, is the vent pipe from it sealed/blocked off?

(rocker cover vent went to air filter pan)

and is your oil filler cap the vented or non-vented type?

have your carbs got provision for the breather pipes?

I know it's not macho to read an instruction manual but the Driver's Handbook has good clear illustration and text on the correct reassembly of the valve - I'm not saying you did but could you have put it back together slightly wrong or it might have been wrong before you took it apart

as your car has some variations a photo like that of the Marina engine bay might help
Nigel Atkins

My car has a Marina engine due to it's oil filter, but all the ancillaries are from it's original 1098cc engine (I think).

The twin carbs do not have any way of fitting the 'y' piece connector that was used on later engines, hence why I went 'pcv'.


I've had a look at the 'driver's handbook' didn't realise it was anything other than "this switch operates the ...", so thanks for that, however I appear to it reassembled correctly !

Just checked the engine, it does have the rocker box pipe, the oil filler cap is not vented.

I'll get a piccie tomorrow

Malc Gilliver


2 points to check:

The rocker 'bent pipe' should be sealed off when there is a 'closed circuit' crankcase ventilation system - such as you have. The only air inlet is via the oil filler cap.

The oil filler cap MUST be the vented type - it provides some of the control for the partial vacuum being created by the PCV. It needs this to keep the oil inside the engine, but not too much vacuum or it will suck it out through the PCV!
Richard Wale

sounds like you've a mix 'n' match breather system, the system is as Richard's put (only the rocker cover would normally be without a pipe to block off)

the earlier set up was rocker cover pipe then rubber hose to air filter pan with solid (non-vented and filtered) oil filler cap

once you've got the breather system set up have a look in the Driver's Handbook for a simple test to check it's working, if it's like my DH it's fully of instruction and diagrams on servicing the car and full of relevant correct information that I've seen not used here many times because some think they know when they don't or have forgotten or too macho (or butch) to look at such books

Nigel Atkins

A few points....

1. Do you have a hole in the oil cap...about the size of a needle

2. Is the hose from the oil sperator to the carb a stiff hose... if its flexable, that can cause it to collapse and suck in on its self

3. Put a boost gauge on and look to see if you got a positive or negitive oil pressure in the crankcase

4. To me it sounds like you have positive crankcase pressure... most likely a busted piston is my guess

Just a side note... the purpose of the oil seperator and its gauze is the oil is sucked up as a mist during the evacuation of the evac system... the gause catches the oil mist, as the captured oil mist is cooled it converts back to liquid oil and drains back Into the engine..

This is why the gause has to be as loose and spread open and free breathing as possiable and not crushed, collapsed and wadded up into a tight ball


Prop and the Blackhole Midget

A few points....

1. Do you have a hole in the oil cap...about the size of a needle

2. Is the hose from the oil sperator to the carb a stiff hose... if its flexable, that can cause it to collapse and suck in on its self

Put a boost gauge on and loom to see if yout got positive or negitive oil pressure in the crankcase

To me it sounds like you have positive crankcase pressure... most likely a busted piston is my guess

Just a side note... the purpose of the oil seperator and its gauze is the oil is sucked up as a mist during the evacuation of the evac system... the gause catches the oil mist, as the captured oil mist is cooled it converts back to liquid oil and drains back Into the engine..

This is why the gause has to be as loose and spread open and free breathing as possiable and not crushed, collapsed and wadded up into a tight ball

Prop and the Blackhole Midget

If you have not changed anything except cleaned, checked, and reassembled as it was then no part should be a problem. The only difference is the blast up the road.

Lots of oil smoke from the exhaust and high crank case pressure causing oil leaks are indicative of excessive ring ware or blow by. I would first check the cylinder pressures and see if all the same and they check against the accepted norm.
That blast with less oil may have caused more ware than you thought.
Even one cylinder with excessive blow by can cause high crank case pressure and leaks.
Believe me; I know.

Dave Squire

Do you still have a problem? Having cleaned and reassembled it I would return it to the original configuration that you were running and then just monitor what is happening. If it continues, then you may have a piston ring problem which a compression test would reveal.

If with the original arrangement (before you added the PCV) the outlet hose became pinched, blocked or maybe clogged it would then cause sufficient backpressure in the crankcase to cause oil mist to be blown out of other orifices - from a loose dipstick or a rocker cover vent. A little oil goes a long way and could look much worse than it really was. Cleaning out the pipe may, of itself been sufficient to solve it.

Your Marina based engine shouldn't need a Vacuum assisted extraction system, either to a PCV or to a carb. The Marina crank has a proper seal system doesn't it, in place of the earlier engines' scroll seal. So oil dripping from the crank "seal" as on earlier engines shouldn't be a problem. The Marina engine should be fine just venting to atmosphere. If you apply suction, then you are very likely to draw up oil fumes and get the resulting smoke screen.

I suggest that you remove the PCV and try it without again,. And do a compression check.
Guy W

I also run a marina based engine and here's a shot of the breather arrangement. Set up is as Lawrence explained - Vented filler cap, no PCV, no breather on the rocker cover but a connection to both carbs via a Y piece from the timing cover.

It has never caused me any problems.

Hope this helps.

Peter B

Guy, the 1800 Marina had such a seal, but all the 1300's I've seen had the same old scroll ... and if you look at Malc's original post you'll see that oil is being pushed out of the engine in undesirable quantities.

And all engines benefit from a closed breather system, proper seal or not. It's one of the main reasons modern engines are as oil-tight as they are. Once they get old and ring leakage presurises the crankcase, guess what? They start to leak oil. Not as much as engines with a scroll, but a few drips just the same.

Between them Richar and Dave's posts will contain the answer.
Paul Walbran

Thanks for the responses...

I thought I'd put it back to standard but I think mix and match might be a better description!

In the carpark of the shop I blocked the PCV and removed the pipe from the canister to pcv, which puts the car in a condition as per Guy's suggestion - ie back to how it was but with no restriction or vacuum on the crankcase breather - so this is how it's going to run for a day or so while I check for oil blowby on the dipstick.

Then a compression check is clearly the next step.

Found this while looking for info on the crankshaft seal

"The rocker from the 1275 does not have a breather tube coming out of the top as with the 1098. It must be fitted with the type using a black plastic cap, through which the engine draws air in at a slower rate than it is expelled. The engine therefore tuns with a partial vacuum inside; this delicate balance can be easily disturbed by incorrect plumbing!"

So it looks like the PO did indeed swap the ancillaries - including the rocker box, so I might treat it to a new alloy box with vented cap.(the GF will be asking "what do you want for Xmas soon!!)


I can find the assy method, but no mention of how to check the PCV in the drivers handbook for the car, can you post or mail me that part ?

Lastly, as Guy mentioned, is the Marina engine fitted with a proper crank seal as opposed to the scroll type ?




I took so long writing, more info has been posted !

Thanks for the picture Peter, I have earlier carbs that can't use the Y - maybe another change..

Thanks for the seal update Paul
Malc Gilliver

"I thought I'd put it back to standard but I think mix and match might be a better description!"

You have pretty much Malc. The 1st 1275 spridgets had the PCV, and if the marina engine has a rear scroll too, then it's not so different. Not all engines get the oil sucking problem. The only thing you have that's non standard really, is that you have an open pipe on the rocker, in place of a filtered vented oil filler cap. I don't see why that should cause the problem. There must be a different cause. Either too much sump pressure, or something else.

You say, "So it looks like the PO did indeed swap the ancillaries" Yup, and also ran it without a breather. Now you know the why, but not the cause of the why.

I'm guessing you got that quote, --- "It must be fitted with the type using a black plastic cap, through which the engine draws air in at a slower rate than it is expelled" -- from Spridget mania, not a BMC text. That's just their interpretation of how it works. As far as I'm aware it works like this.

The purpose of the earlier pipe on the rocker cover was to allow pressure/fumes to be drawn FROM the rocker cover into the air filter(s). The purpose of the vented plastic gauze filled oil filler cap, is to allow 'filtered' air to be drawn INTO, -- NOT expelled from -- the rocker cover, down through the engine, up through the breather, and into the inlet, via either a PCV into the manifold, or twin pipes to the carb.

Having an open pipe on the rocker cover, allows "dirty" air, instead of filtered air, to be drawn into the rocker cover -- if you have a breather system connected. So, is that air flow a greater quantity than through a plastic vented filler cap? And does that allow for a column of oil to be sucked up into the engine via the breather canister and the PCV? I can't see why it would. There has to be an underlying cause.
Lawrence Slater

"connected the hose from the timing cover to the PCV and since then the car has embarrassed me with the oil clouds."

One thing you didn't say Malc, was if this only happens when cold, or continues to happen when the engine is fully warmed up.
Lawrence Slater

The reason for the PCV valve on any installation is in the name. But without use of a moderating valve system suction at the manifold is too high, will draw oil through into the intake system and result in clouds of blue smoke. The PCV valve manages that suction and keeps it within limits. Unless of course its a faulty valve and isn't doing its controlling of pressure properly, are you sure that the valve is OK?

There may of course be other problems. If you do find a fault, don't assume its the only fault.
Guy W


>>I can find the assy method, but no mention of how to check the PCV in the drivers handbook for the car, can you post or mail me that part ?<<

yes of course but I will need your email address :)

or email me on my address here if you want to keep your address off a public forum

I'll scan the relevant page and email it to you, of course it relates to the standard breather system so I don't know if it would be the same for other systems

[b]IF[/b] you need a black plastic vented/filtered oil filler cap buy the £4 ones (available from MGOC Spares) and not the £10 ones from others
Nigel Atkins


Does the curved vent pipe on the rocker cover have a plug in it with a small hole drilled in the button? I know some of the Bs did, and the hole was to limit the amount of air that could be drawn into the engine. With that button limiting the inbound air flow, a non-vented oil cap was used. The rocker cover vent connected to the charcoal canister so that it did not draw in dirty air.

When this arrangement is used on a car with out the charcoal canister, a small filter can be added to the rocker cover vent to stop the dirty air from entering the engine. If your rocker cover has no limiting button, you could plug and drill it. I can't remember the size the hole should be, but someone else probably does or I could try to find it. It is something in the neighborhood of 1/32 inch.

If you have the limiter in the rocker vent, and you have a non-vented oil cap, then I would suspect the condition of your PCV valve. If you don't have the limiter in the rocker cover, then I suspect you are allowing the PCV valve to draw too much air into the engine.

If you can see it in the pic below, this is the set up on my B. I did not have a vent in the rocker cover since it was an aftermarket alloy type. I drilled and tapped an oil cap and installed a barb type brass fitting. I brazed up the hole in the barbed fitting and drilled it out to the size of the button in the original type valve cover. Then I ran a rubber hose from the barbed fitting to a small fuel filter. I used the same mushroom type PCV valve that you have, which I connected to the timing cover canister.


C R Huff


Blue / Black puff of smoke on start up - oil and choke.

Then puff off blue / black on gear change on choke.

Choke in, puff of blue at each futher change, then engine / oil warms up and it gets a constant blue trail, that gets worse!

Must note however the first time I drove the car after fitting the valve it did all this, went thru warm to hot and stopped blowing blue smoke so I thought it had cleared it's throat.

Re-telling the sequence however and everybody will spot the hotter thinner oil and excessive vacuum and come to the same conclusion !

Thanks for the ABC description, I wasn't aware that on 1098's the system operated in reverse - ie out of the rocker.


It does look like a change of cap and rocker box will fix most of this, doesn't it ?


I've mailed you to ask for the driver's handbook and thanks for the tip on the cap.



Thanks Charley, I think we agree !
Malc Gilliver


Also, go look at the thread about the air cleaner decals. There are a couple good pics of the 1098 system there.

C R Huff

<<a change of cap and rocker box will fix most of this>>

Unfortunately Malc, I am not so sure that it will. But I do think it is important to check the easy things first and not venture into the complexities too soon! And I wasn't absolutely sure from earlier discussions that you mightn't have already cured the problem just by cleaning out the pipes, without needing to add the PCV valve on that engine. I did think they had the improved crank seal, but Paul corrected me on that point and I am pretty sure that he knows better than I.

The right amount of restriction of air going in is important though. Too little and it will just suck a gale of air through the crankase, picking up far too much oil and water vapour on the way. To little, and the system is strangled and won't flush the nasties out! Get the proper vented cap as Nigel describes. And block the open redundant breather to the rocker cover. Too much air in = too much air and oily substances out = blue smoke.

Get those bits right first. If there is still a problem then there may be too much blowby but that is a whole new issue best not worried about just yet!
Guy W

I'm with Guy easy stuff first before moving on (especially as I've no idea of more complicated stuff)

plugging that (possibly wrong) rocker cover vent pipe is easy to do and reverse as is and/or vented/filtered and non-vented filler cap

having the help and guidance of the text and illustrations from the Driver's Handbook also eases problem resolution many, many times and the use and reference to the good book also many, many times prevents problems
Nigel Atkins

Why not just post the instructions here Nigel?

Lawrence Slater

This discussion has now become very interesting.

" --- then engine / oil warms up and it gets a constant blue trail, that gets worse!".
" --- the first time I drove the car after fitting the valve it did all this, went thru warm to hot and stopped blowing blue smoke so I thought it had cleared it's throat" ----.
" ---- everybody will spot the hotter thinner oil and excessive vacuum and come to the same conclusion ! ".

That's just about the same description as the other circa 20 descriptions I've found in the archives Malc. This is the first on a Marina engine, but it seems you're engine is sucking a continuous column of liquid oil into the PCV/inlet manifold, just like the others.

Did you buy a NEW PCV? If so, then as graeme found, there's likely to be nothing wrong with it. So how is it able to suck so much oil up?

I was about to say, --- I positively don't agree that letting too much air into the rocker cover will cause a column of oil to rise up from the sump into the PCV. If that was the case, then removing the filler cap when the engine is running would result in the same thing, when you opene(low vacuum) and close(high vacuum) the throttle. I was also about to say, that this talk of the oil filler cap being very air restrictive is wrong. I was about to say, in fact they aren't. There are quite large slits around the side that allow air flow into the cap, along with a pretty large exit hole that allows the air out and into the rocker cover. Take a new one, stick the smaller round end in your mouth, and you can breath through it easily. You can suck just about as much air through the cap, as you can a half inch pipe.

HOWEVER, I'm not going to say that anymore.

I just looked at the oil filler cap on my '73 Midget, and got a surprise. So I looked at the filler cap on my '66 Sprite, and got another surprise. They aren't the same.

The cap on the left of the picture is from my Sprite. The one on the right is from my Midget. Spot the difference. Could it be that there was one type for a PCV, and another for the later Y piece arrangement into the carbs?

Take a length of pipe, and block one end with your finger. Half fill it with water, and suck on it.
You create a vacuum above the water, but can't suck the water up, because an equal vacuum is formed behind the water. Gradually release your finger, and keep up the suction, and the water rises up into your mouth, because there's no longer a vacuum pulling from behind. The more you release your finger, the easier it is to suck up the water.

The breather system is pretty much the same thing. Suction from the inlet manifold, and resistance to air entering at the rocker cover. So having an open pipe on the rocker cover, instead of a more restrictive vented plastic filler cap, or, an air hole that's too large in the oil filler cap, allows for easier/greater air flow into the engine, and hence less pull on the oil from behind. Maybe that combined with too much crankcase pressure could cause the oil to be sucked up, and maybe that's been the missing factor all along.

Are there different plastic vented oil filler caps on sale, for the earlier and later breather systems?

Can someone else post a picture of the underside of their plastic vented oil filler cap?

Lawrence Slater

in my later version of the good book it gives additional useful info, probably added from feedback(?) -

Clean the diaphragm (3) with detergent or methylated spirit.

Replace components showing signs of wear or damage.

Reassemble the valve, making sure the metering needle (4) is in the cruciform guides (5) and the diaphragm is seated correctly.
Nigel Atkins


I have a Marina engine in my Midget and I've been through issues with breather set up. When I bought my Midget the breather pipe went from the rocker to the "Y" piece at the carbs as there was no breather off take and canister from the timing cover. Some people will remember my posts on this. Until I found a timing cover which took sometime, I put an oil catch tank (Guys Illy Coffee Can design) between the rocker and the "Y" piece see picture. Perhaps you could do the same but put the catch tank between the timing cover and the PCV. This needed to be emptied every few weeks but was effective in separating the oil from the fumes. I'm sure Guy can post a picture he has of the components needed.

Pete Ottewell

note these are for the 1275 and despite the description and price differences both were as photo when I bought them (I can't say if either is right or wrong or as original)

MGOC Spares - Oil filler cap- Vented GFE6003 [7] - Price: £3.95 Including VAT at 20% -

Brown & Gammons - OIL FILLER CAP OE 13H2296 OIL FILLER CAP OE - Price: 9.58 + 1.92 VAT = £ 11.50 -

(B&G price is up from when I made the mistake of buying one)

Nigel Atkins

<<Suction from the inlet manifold, and resistance to air entering at the rocker cover>> Yes Lawrence, its a balance between too much air flow and not enough air flow. I (and others) have been stating this in various forms for yonks! Its taken a long time to get through to you.;-) Maybe it only penetrated when I put it into a formula form :: "Too much air in = too much air and oily substances out = blue smoke."

It may, or may not be an answer to your problems, but it is important. Your description though of your "column of oil" always sounded to me like something of a significantly different order to the (almost common) blue smoke problem. The latter is very easily caused by either a clogged breather cap, or the wrong type of cap fitted. They are as you say, visually almost identical. Also, its a compromise. Air in through the oil filler cap and air mixture out the breather is only part of the story as there are other sources of air in which vary from engine to engine. The obvious sources being blow by and poorly fitting dipsticks. And of course fitting the wrong type of vented rocker box top!
Guy W

The addition of my Illy can oil separator that Pete refers to doesn't really alter the basic principles behind having a PCV system to lower the crankcase pressure and evacuate fumes utilising induction suction. It is purposefully a sealed cannister system that just provides an additional container in which to precipitate oil, hopefully reducing the amount that gets burnt.

Mine "breathes" as it should via the front timing chamber cover so air is being drawn right through the system collecting all the nasties on the way (oil, water vapour, acidic combustion gasses) YThe problem I would imagine with Pete's arrangement is that, although it will extract and keep the internal engine pressure under control, it will also be short circuiting from the adjacent air feed (filler cap) so not actually purging the crankcase.

Guy W

Er no Guy. Actually I've been well aware for many many moons, that suction from behind the oil, versus suction from the front, has to be unequal to enable the oil to be sucked up.

And there can be no doubt, a column of liquid oil is being sucked up. The missing element has and may still be, the exact combination of circumstances that allow that to happen. The discovery that no one else has mentioned before, that there may be different vented oil filler caps, could be a significant part of what's missing in the explanation.

As for being clogged. If the vented oil filler cap is clogged to the extent that no air can enter though it, then, if no air enters the sump from anywhere else, there can't be any oil suction.

And finally my oil caps are not "visually almost identical". The hole is hugely different on one, compared to the other.
Lawrence Slater

What I am saying Lawrence is that the fairly common fault of blue smoke haze is easily caused by a mis-match of parts, or use of the wrong components. But that this is easily explained. Whereas your "column of oil" scenario is of a different order and scale and much harder to analyse.

The caps are visually almost identical from the top - i.e. when fitted. The different size of the hole underneath is, as you say, pretty clear, especially when you have both types side by side!
Guy W

Then we're still in agreement Guy. ;). But Malc isn't describing a blue haze from my reading of it, and nor are many others, both recently and in the distant archives.

Nigel, I don't suppose you have a clearer picture of the internal hole of that oil filler cap do you?
Lawrence Slater

Guy that's my old set up before I fitted a timing cover that had the canister. i have now done away with the Illy can and the engine breaths as it should do.
Pete Ottewell

Hi Pete, I had forgotten, or maybe never knew, you had updated again since that variation.
Guy W

So all I need to do is get a rocker box without a vent pipe - easy enough and the correct cap, which is clearly going to be not that straight forward.

Moss list two caps - vented and not vented. Lawrence has shown that there are clearly at least three caps - not vented, vented with little hole and vented with big hole.

Given a choice I think vented little hole would be my preference.

Pete, as you have a working Marina setup can I have a piccie of the inside of your cap?

Nigel, as you have a new part with a part number, can I have a piccie of yours aswell ?

and if anybody else want to some me theirs then the more the merrier !!!!


oh yeah and a compression check will be done when I go the GF's later this week !
Malc Gilliver

you need to plug the vent pipe on your existing rocker cover and fit a vented/filtered cap to check and then as someone else has put it may be you have other issues elsewhere anyway

but I bet if you plug and filter there's a good chance things will at least improve

as for the oil filler caps don't assume that any part is correct or original or fully working properly just because it's already fitted to a car

the oil filler cap with the big hole may be from another car and not correct to a Spridget (not that I know) or the cap with the smaller hole that is sold by MGOC Spares and B&G may not be the original type (I don't know) even though it is marketed as OE

the vented/filtered oil filler caps from MGOC Spares going back as far as 6 years to the best of my knowledge have been as shown in my photo (the one with the purple microcloth as background) - it has the smaller hole and all the different oil names on the top

if you need a better photo just ask

if you lived nearer you could have a spare vented/filtered cap to try (and keep)
Nigel Atkins

Thanks Nigel.

If the new cap comes with a small hole I'll be happy and blocking the rocker box is no issue.

Malc Gilliver

if not I can post you my spare

I can remember being told years ago that the plastic ones gave better breathing than the bling chrome ones and that even if you have an alloy rocker cover to use the plastic vented/filtered oil filler caps
Nigel Atkins


My cap is the Vented one from MGOC part number GFE6003 bought at the start of the year if that helps.
Pete Ottewell

I had the oil blowing problem although I have the set up with the pipe from the timing cover going into the Y piece with the carbs. Solved it when I replaced the pipe and the oil filler cap. I managed to get an original unipart one which was vented with the small hole. As a reference the timing cover is the 8 bolt fixing but a later one with the recess and baffle around the gauze.
Bob Beaumont

missed it before but I see someone has requested a clearer picture of my hole - sorry I've not got one but I can report that it the smaller size

if photographic evidence is required to back up my claim I do have the hole and a camera so I could oblige if required but setting up the photo wont be as quick for me as you might imagine

the names on the top are
. B.P.
Nigel Atkins

I just did something intresting a few minutes ago....sorry, It didnt involve photographIing my oilly hole

I set up a catch tank a few years back so the hose from the timing chain oil seperator into the catch can then a 2nd hose from the catch tank to the Y connector to the duel carbs

But this time....

I put in a PCV valve as it comes out of the catch tank...

My hope eventually is to hook a pressure valve on top of the pcv and transfer the hose from the carbs to the intake manifold

Prop and the Blackhole Midget

Prop are you sure you're not drinking the waste from you catch tank?

and I meant to put earlier if you only have a needle size hole it might not be enough as our caps have two rectangular holes at the top of the cap, 3mm (ish) x 8mm (ish) (very approx)

I know as I've just done a light test
Nigel Atkins

I might add the new cap comes with the rolled filter mesh oiled or lubricated in some way - I wish I'd remembered that before I tried the suck test, I don't suppose I'm the first to be caught out by such things, now where's the mouth wash
Nigel Atkins

If you have the choice of connecting to the carb suction, this is probably better. The reason why? : The vacuum pull at the manifold is greatest when the engine is at middle to high revs, but you have taken your foot off the throttle so the butterfly valve in the carbs has closed. This shuts off the air being drawn in through the carb whilst the engine is still trying to suck in, so the vacuum in the manifold goes up. But this is on overrun, rather than when you want it, when engine is generating power and blow by would be at a maximum.

The vacuum connection to the carb is better as it is arranged to be before the butterfly valve, so the suction is greatest when the air is rushing in, i.e. when driving at full throttle, matching the time when blow by will be at its greatest. So it matches the suction to when it is most needed.

Guy W

I bet for at least a test a Sprite will be running around with a 'Midget' oil cap :D
Nigel Atkins

"I bet for at least a test a Sprite will be running around with a 'Midget' oil cap :D" Trouble is Nigel, my Sprite doesn't suck oil now, since I converted it to a single HIF44. -- Less suction then twins I'm guessing.

But that's two people who've confirmed a small hole in the cap. My cap with the large hole probably came from Moss, and is at LEAST 10 years old, probably nearer 20, and maybe even more than that. I don't change them. If they aren't blocked, there's no need. And they can be cleaned. I might even have another in the loft. And it has the same list of names that Nigel listed, in raised lettering on the top.

According to Sussex, 1098,1275, 1800MGB caps are the same vented filler cap, GFE6003. Same from Moss. And that's the same part number in my 30 year old Sprite and Midget centre part list. So if they all have the same part number, are they all made to the same spec, because mine is clearly different.

I don't suppose you have your old one do you Bob?
Lawrence Slater


I have an MGB rocker box with vented bling cap in the shed - be trying that tomorrow - thanks !!!

So Nigel, I'll be driving a Sprite with an MGB cap - lol
Malc Gilliver

I hope you saw my previous post with hole info and offer of photo

13H2296 is the number in the BL (factory) Parts Catalogue and as used by some suppliers

I think the term OE has been applied very loosely for a number of years

perhaps the 'Sprite' cap was originally for another BMC/BL vehicle (car/van/truck/tank?)

perhaps the 'Midget' cap is wrong and originally for another vehicle or it was recommissioned with the wrong sized aperture

what is needed is a genuine original factory fitted oil filler cap that is certified as such or original technical drawings - or someone that has retained this minute detail from back in the day

I only know the hole size in the caps I have because I've had that screwdriver for decades and know its size

bling caps are multi-vehicle - if the car is better with it fitted it might just mean it works better with the fault not that its correct or the car is running as it should :)

just teasing
Nigel Atkins

A tually nigal,

My thought is so connect the intake manifold to the valve cover and the timing cover to the carbs...

Or hook all all 4 connections togather..but I need to do some expermination

Prop and the Blackhole Midget

I'm not sure you ever need to experiment again for the rest of your life

but it's your life (and long may it be so) so I'm sure you will continue your experiments with all of the exciting and interesting results you usually have
Nigel Atkins


Actually im currently making some high performance air cleaners for tomarrow

4 paint can lids, 2 round air filters, and 2 large rubber O-Rings, some rtv sealer, a hard rubber ball, some cork gasket material and some self tapers, 4 carb bolts, maybe some tension springs and black spray paint....

ill post photos tomarrow far ive got about $9.00 in them....hoping to stay under $20 aka $10 each

But yes your correct...ive got alot of experimentation and modification work comming up I want to test for


Prop and the Blackhole Midget


I'll have a look. It was a unipart GFE6003 and in a sealed unipart packet. I bought the last 2 the supplier had. The original one was years old. I hadn't replaced it as i could still suck (nasty) through it and assumed it was ok.

Bob Beaumont

Cheers Bob.

Nigel. I bet your shaft (screw driver that is - :)) is 5/32".

Googling around I've found various descriptions of the evolution of the breather circuit on MGBs. The vented plastic filler cap was introduced along with the PCV, when the system migrated from an open draw pipe on the tappet cover. As the system evolved, the cap stayed essentially the same, with the same 5/32" "restrictor" hole in the underside.

Since the part number given for the MGB is the same for the Spridget and Mini, they must have used the same cap. Why my sprite cap is different -- so much larger --, I haven't got a clue.

I'm still looking for my spare in the loft to see if it's the same. But looking more closely at my sprite cap, I'm wondering if there's something missing. In your picture you show a one piece plastic "restrictor" disc, prised half out, and nothing other than the mesh underneath.

I wonder if my cap was made with a fixed plastic plate with a large hole to retain the mesh underneath as shown, and a seperate restrictor plate with a 5/32" hole in it, over the top. If so, maybe it fell out years ago, and I never noticed, having never compared it to another one.
Lawrence Slater

It looks like I have a problem.

Swapped the non vented cap for the vented bling one of an MGB, took car out for a run, tiny bit of blue on start up, then drove the car until it warmed up again, then massive clouds of blue - only lasts about 2 minutes of driving, then clouds cleared up, so drove the car till it warmed up - no more blue !!!

Parked the car up, removed the top of the PCV and found a large quantity of oil sitting inside the PCV, I'll guess that when I start it up again, it will repeat the whole process.

Picture of inside of PCV.

I think my summer of blasting around the roads is over, engine rebuild for winter - any thoughts ?


Malc Gilliver

Installation piccie

Malc Gilliver

OK. I see you've blocked the vent pipe on the rocker cover. Therefore the only source of air inlet, is via the pretty small hole in the chrome cap you've fitted.

In theory, the smaller the hole, the less the suction effect will have in pulling oil up from the timing cover. But you're still pulling oil up.

When I first had this problem, I was using EXACTLY your setup, with a PCV into the manifold, and with the exception, that I had a plastic vented filler oil cap.

1). Get a "clear" plastic pipe to replace the hose from the timing cover to PCV. This will enable you to see that the pipe fills completely with oil.

2). Just in case it does make a difference, fit a new 'plastic' vented oil filler cap.

3). You didn't confirm if you have a NEW PCV, but looking at the pic, I see rad paint, so I guess it's old. If old, is there a pin prick hole in the diaphragm? Is the spring too weak?

4). I wouldn't strip the engine just yet. You are unlikely to find anything. I did strip and rebuild the engine. I didn't -- at the time -- find anything, and I didn't fix the problem.

PS. You don't have to be driving along to test this. Just let the car get cold over night. Warm it up on the drive. At a certain point it will start to suck oil as you gently open and close the throttle. When it happens, if you have a clear plastic pipe fitted, remove the oil filler cap, and see what happens.
Lawrence Slater

PPS. I timed out, so I'll repeat my last bit.

You don't have to be driving along to test this. Just let the car get cold over night. Warm it up on the drive. At a certain point it will start to suck oil as you gently open and close the throttle. When it happens, if you have a clear plastic pipe fitted, as described in my point 1) below, remove the oil filler cap, and see what happens.

Does it get worse, or does the oil drop back when you remove the oil filler cap?
Lawrence Slater


I got the PCV from an MGB after checking the part numbers were the same, I just cleaned it and checked the diaphragm wasn't damaged and reused it, I'll buy the new cap and a new diaphragm this week.

Malc Gilliver

What timing cover have you got on your marina engine? Is is the later type as fitted to A+ engines? There's some speculation that a splash ring in the later type, might prevent this kind of oil sucking. If you have one, that theory is dashed.

And good luck with this Malc. I've had this problem since circa 1980. You might have a long road ahead. :).
Lawrence Slater

So lawrence, why doesn't it happen in all Midgets fitted with the PCV valve? Or for that matter when fed directly to the carbs as per the later variant. Most don't have the problem at all ... I'm not doubting that your's is doing it, but I've never seen it happen with any cars so fitted - and I suspect if some checking was done that would be the case with the vast majority. In fact given it was an early emissions device, a great gob of smoke when the cars were being sold new would be completely counterproductive and have had the US authorities leaping up and down energetically. So it's not inherent in the design and wasn't happening when the cars were new - there's something not working as it should to cause what you are seeing.
So an explanation has to account for this.
Paul Walbran

Lawrence - "Trouble is Nigel, my Sprite doesn't suck oil now, since I converted it to a single HIF44. -- Less suction then twins I'm guessing." I don't think so. It's the same 1300cc engine sucking through it all, there has to ba another explanation.
Paul Walbran

PS: Be aware that some of the "GFE6003" caps are useless copies. (This will be no surprise, and let's not divert down that track for now)
I get better ones under 13H2296. They are much more expensive but do the job properly.
Paul Walbran


slpj24 ?
Malc Gilliver

Just for the record, I have just checked the filler cap on my marina block engine and can confirm that its the small hole type and its been on for many years with just the occasional clean of the mesh filter.

I am following this thread with interest as I have been planning a carb change and recognise that this might upset the venting arrangements. Am I right that some HIF44s don't have a suction take-off before the butterfly?
Peter B

I have a non A plus timing cover but it has the spash ring. I did have the problem until I renewed the pipe from the timing cover and the filler cap.
Bob Beaumont

I've just spent a few hours reading as many PCV threads as I can and I notice that they seem to end quickly because the answer was fairly obvious , or just end without an answer.

Some of the threads that seem to replicate my problem, which I'm coming to think of as a cold oil, startup oil suction problem don't appear to have conclusions - gulp !

Is the 'splash ring' a crecent shaped rib welded inside the timing cover ? - if so it has one.
Malc Gilliver

I think the problem has to lie with your Pcv

Because the pcv sits on top of the intake manifold and the intake manifold pulls between 9-12 psi of vacume ( not sure what that is in bars ) while the duel carbs pull less then 1 psi

So my thinking is the pvc is pulling way to much vacumy way of the intake manifold and its tryjng to suck the equivalent of a bowling ball out of your crank case...if you can reduce the vacume that the pcv is pulling to under 2-3 psi (im purly guessing and pulling that number out my donkey) I think you would be good to go

To be honest. At this point... you need a cheap $10 boost gauge to measure whats going on...otherwise, your just guessing

I say use a boost gauge over a vacume gauge because a boost gauge will measure both positive pressure and vacume pressure

Personally id love to know how much vacume you are pulling at the pvc when the car starts smoking blue oil....or even if it is vacume.. it could be positve pressure



Prop and the Blackhole Midget

Wow.... I just had an embarrassing thought

Any chance you have the wrong dip stick and the crank case is over flooded with oil ?

Prop and the Blackhole Midget


Because of the car's bitsa history I actually measured the oil in and then checked the dipstick, but good idea anyway !

I've pretty much come the conclusion that I have way too much vacuum - one thing I haven't checked is the bent pipe on the rocker box - if that has been blocked, then no air in, fitting the vented bling cap only allows a tiny air flow in, possibly not enough, so I'm considering some steps.

I have just cleaned the PCV out and reassembled, so I think the only way to reduce the vacuum is to drive the car with the rocker box cap off - maybe put a clean cloth over the top and secure with a tie wrap, having seen pictures of all the other vented cap, they do seem to allow much more air in than the bling cap, so here goes !!!

Then once it's warm and not embarrassing me I'll do the PCV valve check thing.

Malc Gilliver

Took rocker box cap off and drove the car, no change at all, pretty much no blue smoke until the temperature gauge moved off 90, then at exactly the same place on the road, great clouds, till it burnt it off again.

It does seem to be a large intake of oil either at start or just after then a burn as everything gets into the intake, then it fizzles out again.

Help !!!


Good job I live on the edge of Tamworth, the local flora and fauna will be oily soon, least the neighbours don't see it going or coming back !
Malc Gilliver

pity it's not working

I've bought GFE6003 (£4 from MGOC Spares) and 13H2296 (£10 at the time, from B&G) and AFAIK they were both the same, no difference in quality

I don't know if you saw I checked yesterday and the GFE6003 cap has two rectangular holes at the top of the cap, 3mm (ish) x 8mm (ish) (very approx), the filter is a roll of folded wire mesh that is coated in some sort of oil or something, the hole in the base is 4mm diameter

(the screwdriver shaft is 1/8")
Nigel Atkins

Hi Paul.
-- "So an explanation has to account for this." -- Yes indeedee. I'm a great believer in cause and effect, and I don't believe in magic, one iota. lol

I'm not going to rehearse everything I've already said in previous threads. It's ALL there in the archives to be read, INCLUDING, what are obviously engines sucking columns of liquid oil into the engines. And Yup, not everybody found a solution. And yup, some just ditched the breather system to get around the problem. Some fitted catch tanks. Some sold the car with the problem, And some as Malc has found, just stopped posting about it. And some more have a different problem.

Why doesn't it happen in all Midgets fitted with the PCV valve? I haven't a clue, and nor does anyone else. Why does it happen to only some engines using the Y piece into twin carbs? I haven't a clue, and nor does anyone else.

Fact. On the 1st 1275 engine in my car (when it was 12 years old), using a PCV into the manifold, my engine sucked oil, AFTER it was rebuilt, with new cam bearings, new cam, a newly ground crank, new pistons to +20, on a standard Spridget head with new valves, seats, guides and stem oil seals. I swapped out the PCV, for a y piece into the carbs. It still sucked oil. I put up with the oil sucking because nobody at local garages, or BMC technical in Oxford, had any idea why it was happening, or had heard of it. So I obtained an additional 1275 engine to build.

Fact. I rebuilt the additional engine to +30, new pistons in newly bored cylinders (different machine shop), freshly ground crank, new piper270 cam, 1300gt head with new seats, guides, valves and oil seals. Breather into y piece into twin carbs. It sucked oil from the 1st time it was started, as soon as it came up to temperature. -- just as many people describe. I took out the cam and put in a standard cam. It still sucked oil. I lived with it for over 100K miles, until I rebuilt my 1st engine again.

Fact. The engine currently in my Sprite is back to the 1st 1275 engine described above. I rebuilt it with cords rings onto the same pistons, bores were good. New shells, crank was good. Peter Burgess fast road head. New standard cam, same cam bearings as they looked good. It sucked oil as soon as it was warm. It was using the hose to y piece connection to twins carbs.

Fact. It stopped sucking oil when I changed the twins for a single HIF44, and did nothing else. I wasn't expecting it to stop sucking oil, I just changed because of wear in the carbs. But for some reason, if not less suction, the oil sucking stopped. When I get around to it, I'm going to refit the twins and see what happens.

Oil filler cap.

--- "Be aware that some of the "GFE6003" caps are useless copies. (This will be no surprise, and let's not divert down that track for now)" ---

Why not "divert" to discuss this? It's as relevant as anything else. As for being useless copies. All it does is allow air to enter the rocker cover. Mine has a hole too large when compared to others that appear to have the correct sized hole. In the absence of any other conclusive and workable explanation, "diverting" to discuss the oil filler cap seems a legitimate excursion to me.

Malc. If I read you right, you have eliminated the oil filler cap. Allowing more air in, in theory, could exacerbate the problem. But as you say, the chrome cap has a smaller inlet than the plastic version, and you still get the problem. And now you are starting to think of all the same things I tried. Too much vacuum? Reduce the internal diameter of the hose from the timing cover. It didn't work on mine. Try it on yours.

Nigel, yup 5/32 is nigh on 1/8
Lawrence Slater

Are you saying you actually drove the car with the valve cover removed ?

Im having a hardtime wrappjng my mind around that image :-)

A better direction I would persue, would be to make a mock oil cap with a food container lid similar size that can fit easily and some duck Tape ...

Hook up a boost gauge / vacume gauge on a long tube to the steering wheel ...then just experiment with drilling differant size holes in the make shift oil cap and comparing the results with the gauge readings

But thats just me... im sure others would have a differant approach

But I really thing you need a cheap boost or vacume gauge at this point to see whats really happening

But I agree ... I think you have way to much vacume and that could mean you just need a less constrictive air filter assembly...

The more constricted the air filter assembly, the more intake manifold vacume

Im not saying thats the problem... but with A vacume guage you could easily measure and account for that

Prop and the Blackhole Midget

Malc. Mini Forum? Sounds like you've found my thinking on the cam plate. It's one of my theories.

People won't thank me for raising it here, but if you read the thread "engine breather" in the technical archives, last post 22 August 2013 at 21:40:59 UK time, you can read all about it. Scroll down the thread to circa 20 February 2012 at 21:22:39 UK time. Enjoy. lol.
Lawrence Slater

Thats so strange the change of smoking and not smoking would occur at a tempture point event

That almost makes me think the viscosity of the oil is changing at a certian tempure point and becoming thinner and thus allowing alot of blow by because the oil is thinner and cant seal the piston to cly gap as well just purly guessing at that...but I cant imagine what else would cause smoke clouds at a certian temputur change event

Prop and the Blackhole Midget

One thing you could do because you have the older carbs without the Y tube connections

They make add on spacer blocks with a carb vacume ports....

you could add those on and get a Y piece and hook on to those add on spacer blocks and get the same effect as the carbs that use the Y pipe, plus there not very expensive and easy to install

Prop and the Blackhole Midget


I drove it with the rocker box cap off, haven't checked under the bonnet yet for all the oil it has probably blown everywhere !!

Thanks Lawrence, so crush it and fix my V8 powered kit instead then !!

I'm more and more convinced that there is a simple syphon being created, probably as the engine cools, the oil pools somewhere in the timing cover and then on start up the suction drags the 'pool' of oil into or up the vent pipe, the warming oil behind the 'pool' releases the vacuum and the 'pool' heads up the pipe and into the PCV.

So I need to either disperse the 'pool' or put a device in the pipe between the timing cover and the PCV to somehow disrupt the 'pool'.

If my 'pool' theory is correct, then it follows that maybe an issue with the interface between the timing cover / front plate and block, that may have a blocked or missing passage way / different sump, damaged sump or different baffle type feature.

If I'm wrong, crushing it or setting fire to it becomes a possibility !!!!

Prop's idea for the vac gauge might help prove / disprove the pool theory
Malc Gilliver

Round and round and round and .... so on.

A (new) pcv fitted to my 1275 engine (with good equal compression on each cyl) when connected to the manifold suction point one end and the timing cover breather the other pulled up so much oil on tickover the world went blue. It only happened when the oil in the engine was near max suggesting that it has something to do with the levels in the timing cover. It's no good saying "it can't happen.".. it does, end of!

Not on every engine, but no-one seems to know why. You are talking of potentially high suction pressures and if the oil is there in sufficient quantities to flood the breather in the timing cover, it will lift it out! My engine wouldn't stop because it was dieseling on the oil!

Simple solution: remove the pcv and throw it up the garden. Use the manifold tap for a servo instead.
GraemeW (Kent!)

Fhere $ 10 @ harbor feight...and it can tell you alot about everything if you google how to read a vacume gauge

I not only have one... ive got 2 vacume gauges built into my interior and each is on a vacume spliter....

sooooo I actually have 4 vacume gauges at a push of a button

Prop and the Blackhole Midget

Thanks Graeme,

Makes sense, oil levels are highest at start, especially after a drain down.

Time to check the dipstick, then measure that distance down with a vernier and work out where the oil is sitting relative to the block.

Trouble is if I through the PCV away I'm back to cleaning the engine bay after a long drive and oil consumption in the order of 1 litre / 100 miles ish.

But I like your thinking

OR just drive it till stops blowing oil and hope there is some left in the sump !!
Malc Gilliver

Exactly graeme,

I have to belive he PVC is toast defective or has been accedintly been reendered defective

I think a vacume gauge will show there is alot of vaCume being pulled thur the PVC

Prop and the Blackhole Midget

Not if you use the add on carb spacer blocks with the built in vacume ports

Mini spares

Prop and the Blackhole Midget

why not try draining (or sucking) about a pint of oil out of the engine

I've found on some classic cars that once the oil drops to about about 8 tenths on the dipstick it seems to settle at that point, the reason I don't question, I just accept that's where it's best at, same with other fluid levels

talking of which, you seem to have the windscreen washer fluid set for an Arctic winter
Nigel Atkins

Malc: in my case I fitted the kit (with the intention of stopping the oil puddles from crankshaft seal leaks) drove around and all was fine. At some point I decided to check the oil and is was just above minimum (hadn't been checked for some time) so I topped it up.... and "where am I?" moment. The world and the garage was impenetrably blue.... on tick over.

At one point I drained out all the oil and refilled a measured amount to check I didn't have the wrong dipstick!

There are it seems two known World Problems with these cars which polarise owners' opinions and to which there appears to be no definitive solution. This is one - the other can't be mentioned any more.

I could chuck in the issue of spare wheels - that would make three!
GraemeW (Kent!)

It does sound like its over filled

But here is a link to some add on carb spacer blocks... there incorect but you can see the concep

Prop and the Blackhole Midget

Victor Meldrew moment. I can't bloody well believe it.

Graeme, you said it right. "Round and round and round and .... so on."

I'm coming rapidly to the conclusion, there is little or no point in posting ones thoughts on here at all. All this forum seems to be good for, is to gain information, not to give it, since most of the time it's simply lost in the archives, or ignored at the outset.

Prop, I recall you once proudly boasting that you weren't bothering to read the engine breather threads. If you had done though, you wouldn't be making the posts you're making now.

"so crush it and fix my V8 powered kit instead then !! " Nope Malc, keep looking at the problem with an open mind. If you want to know the oil level in the sump relative to the timing cover etc, then look in the "engine breather" thread I quoted earlier. See my post 22 February 2012 at 18:11:57 UK time. There's a nice picture I posted showing the oil level at maximum.

Hi Bob. Yours still throws me. "I did have the problem until I renewed the pipe from the timing cover and the filler cap". Your original description suggested it was the same problem as on mine and others, and yet you fixed it simply. I've done both the things you've done and still had the problem. And now Malc has pretty much done the same. So how was it fixed on yours? I can't see how the pipe being renewed fixed it. Having been surprised by my filler cap, I was begining to see how the filler cap could have been the cause, until Malc did his recent experiment to undo the theory.

Lawrence Slater

Any bets on this going all the way to Christmas and over 400 posts?

Malc, Bob. As both of your timing covers have the splash ring, that saves me bothering to put one in my timing cover when i rebuild my engine, since it doesn't solve the problem.

Peter B. Yep you need to get an HIF carb with the pipe for a breather connection. You're right they didn't all have them.
Lawrence Slater


I do find it quite difficult to get info from the archives, as on so many there wasn't a solution and once they disappear off the front page, then you have to guess what the post might be titled, PCV, engine breather, oil smoke, leaking crankshaft oil seal etc, be nice if we could tag the posts, maybe with a solved or helpful tag and then when somebody posts something helpful other people could 'thank them' so you get a forum where it's easy to see if there was a fix and who on the forum has been thanked for their help.

For the record, thanks to everybody for all the help and advice I received, both on my breather problem, panhard rod and ...... the front wheel bearings !!

Malc Gilliver

Ah! dark evenings, cold garages, if we can't work on 'em, we can at least start some gigantic threads! Where did we get to on front wheel bearings? (Second thoughts, the cold garage has its attractions!)

But back to this one, I do know Prop that my sump isn't overfilled (I measured it in according to the good book and the dip-stick confirmed that too. I also ran the car with a flexible on the timing cover breather running into a catch pot. Never any oil, proving in my mind it was sucked rather than pushed by crankcase pressure.
GraemeW (Kent!)

Just reading the 414 posting that Lawrence directed me to ..."and I was braking reasonably hard. And this sounds daft, going down hill."

Thats the perfect description of the corner that is currently spewing blue smoke.

I accelerate up the hill, brake , turn hard left and accelerate down the hill, in full stealth mode.
Malc Gilliver

Malc. That thread is the most comprehensive discussion on this topic. There are others, but that contains the full discussion.

Glad you found it. For other who may be interested, lol, see "engine breather", 414 posts, last post 22 August 2013, in the technical archives.

Everything about this was discussed in there with the exception of the size of the small hole in the plastic breather cap.

Regarding your theory of "pooling". Again in the above mentioned thread, see posts from 20 February 2012. You'll see that there's nowhere for oil to "pool", unless the drain holes in the main cap are blocked. When you switch of your engine, it's hot, as is the oil. So it's thin enough to drain away through those holes, and back into the sump. When you start the engine, hot or cold, the timing cover is essentially empty of oil. It's what happens in that first warm up period, as you've found, that determines if oil builds up in some way, in a sufficient amount in the timing cover, to be sucked up into the PCV. That in a nut shell is what this debate is about. Some say there is a residual "snot" like slug of condensed oil left behind and that causes the masses of smoke you report. I don't agree. I say that for some reason as yet not detewrmined, the timing cover is filling with oil. when it reaches a crucial level in the timing cover, high vacuum ensues and takes upto 1/3rd of a pint of oil into the intake -- either the PCV or the Y piece connection to the carbs. Others dispute that this is possible. I know it happens, at least on my engines and I believe on others too. Only you know what you are seeing.
Lawrence Slater

Just picking up on one of your comments

"Both of us try to take action to minimize the oil suck by lowering the revs, so we give time for the drain to "catch up" with the supply."

I did the first time, but subsequently opted 'burn it thro" and literally thrashed down the road, it made no difference.

First time, turned the corner "oh sh*t, god this bad', drive it gentle got to the island at the bottom, turned around, drove back up the road and cleared at the junction I turned in to the road at.

Repeated this with the rocker box off, burned oil at exactly the same spot - literally within a car length, so I booted it all the way down the road(60 limit) to the island, turned around and it cleared with in a car length of the junction, I'm convinced the PCV inhales a slug of oil of the same size each time and then burns it.

Oh yes, 80 ish psi on start
Malc Gilliver

Oil Temp v grade graph.

I know we all use 20w50, but at 0 deg C you are at the limit of the ability to pump the stuff

Malc Gilliver

One Hundred! LOL.
Lawrence Slater

Aha, quite a bit of lively discussion while I've been ZZZZZZZZZZZZZ :-). Lawrence I certainly don't doubt the cloud of smoke you describe, I just see that because most don't do this and a few do, then this might lead to the clue as to why. Other engines are fitted with this PCV calve - do they do it or not? If not, then it's not a function of the valve or breather system itself and likely a function of the take-off point (as per Lawrence's explanation).

The only MGB's I've seen issuing huge gobs of smoke like this had a malfuctioning valve, and were cured with either a new diaphragm or a new valve. I've never seen one with the PCV provided via Y-piece and carbs do this.

The big advantage of fitting a PCV system of either type (valve or carb body) is that it slashes the amount of oil leaking - especially in a geriatric design which doesn't have a rear crank seal. A friend has retro-fitted one to his TD, with the result that the oil leaks are reduced to a thumb print size instead of a puddle, and he is no longer afraid to park in friends' driveways :-) Interestingly he has used an oil separator from an MGBV8 between crankcase and valve. How it performed without this I don't know.

PS what I meant about not diverting down that track was rubbish parts in general, not whether a rubbish cap might affect it and if so how.
Paul Walbran

there are a few of us that haven't just used 20w-50 which I found made starting in the coldest parts of winter sluggish (my car is always outdoors)

a mate runs his Marina extracted engine on Magnatec 5w(or 10w)-40
Nigel Atkins

100 post going for 400 comments?

Lets be honest for a change... we dont do this because we have a genuine jesus heart and want to help people.

No we ALL do this because we love the puzzle and being the 1st to solve it is like crack mainlined directly into the blood stream.

Come on... admit it, im not the only one that embraces vanity as there favorite sin

Some days I feel sorry for the pour guy that simply wants to know how to check his tire pressure, we should call our selves a pack of badgers...relentless to get the newbies car fixed and get that feather...hahaha

Im not pointing a finger except 4 back
to myself.


Prop and the Blackhole Midget

Yup it's cool Paul. I'm just getting tetchy because I feel compelled to post. LOL. I made myself a promise not to raise this subject again, and then along comes the spider weaving the oily web all over again. So much to repeat and refute all over again, with never a clear answer in sight. Think I'll just watch from now on, --- if I can manage it lol.
Lawrence Slater

Thinking about oil drain back

What sump does a Spridget have ?

My Marina engine has a reduced depth at the front, then the back half is much deeper.

Can't find a picture
Malc Gilliver

I have checked the old filler cap ( why have i kept this??) against the new one(genuine NOS Unipart) and the hole in the middle is small on both of them. I have no idea why changing the pipe and cap cured the oil problem
Bob Beaumont

Cheers Bob.

Malc. 1275 Sprite engine showing shape of sump.

Lawrence Slater

Malc, that sounds like a Marina 1800 sump?
Paul Walbran

OK Gents I’ve been following this (and the previous thread) with interest and I’ll pitch in now to help get this up to the 500 mark. Lol

Given Malc’s and Lawrence’s experience it’s a fair bet the oil is getting sucked up the tube to the carb when it shouldn’t (massive understatement lol).

One way of confirming this (other than using clear tube) on Malc’s set-up is to do the run again but with the PCV closed. This can be done by fitting the valve in the body but with the spring between the valve and the diaphragm, thereby exerting full spring pressure to hold it closed. As people have observed this may/will increase the crank pressure in a poor engine and running with the filler cap off/loose will help release this in the short term.

I find the discussion on the hole size in the cap interesting and will come back to this in a little while as I think it might be important in the wider context of the PCV operation.

The principal of operation of the PCV is that it is closed at idle (approx -.5 bar) and hard acceleration (approx -0.8 bar) and open at steady cruising (approx -.2 bar). Thus allowing crankcase pressure to be relived without sucking the oil out of the bottom end. The valve closes by atmospheric pressure acting on the outside in the diaphragm causing the valve to close when the pressure in the inlet manifold drops. The spring sets the pressure differential required to close the valve, which is probably around -0.25 bar.

Now, there are a number of issues that could cause the PCV to not work correctly, the obvious one being a split rubber (always dangerous LOL). But also the following:-
1, blocked hold in the PCV cover plate preventing the atmos pressure reaching the back of the rubber
2, excessive spring tension caused by a long period of work hardening (possible I suppose)
3, excessive crankcase pressure that can’t be reduced by the manifold vacuum
4, a filler cap that allows too much air in to the engine to the point that manifold vacuum can’t deal with it.

In 3 & 4 the car would run very weak at all engine speeds and would be a pig to set up correctly (just like my 1300 which fortunately has the take off on the top of the drop gear chamber well away from the oil in the timing chain area).

Therefore Malc, running with a PCV and no filler cap will make things worst by preventing the build up of –ve crank pressure at idle and acceleration (particularly hard acceleration) which is needed to close the PCV.
The size of the hole in the cap may have more significance than at first thought as it is this that restricts the amount of air entering the engine and therefore the amount of –ve pressure built up which is required to close the PCV. In addition, excessive piston blow by or worn valve guides will add to the potential for +ve case pressures which will result in the PCV remaining open.

If you are still reading, thanks and if you understand all this, please chip in with recommendations and solutions.
Mine are:-
1, move the breather take off point away from the timing cover or at least move it higher up the cover if, as it appears, there is a potential for a pool of oil in the bottom (not great for the show cars).
2, get a small hole filler cap.
3, fit a new PVC
4, Remove the PCV and vent with Y pipe to the carbs (constant low pressure (not vacuum) point the subject of another thread if required)
5, If you can’t do 4, route the breather pipe into the air filter on the carb side of the filter (similar low pressure point as the carb position) but be prepared to replace filters more often.
6, on a worn engine, fit a non-vented cap. This might seem counter intuitive but if the engine is producing it own +ve case pressure a vented cap will be unnecessary.
7, recondition the engine and hope for the best ;)

Best of….

M McAndrew

It's no good, I simply can't resist. Welcome to the machine Mike.:) Firstly, this problem isn't confined to engines with the PCV, even though Malc is running one. it happens with the Y piece too on some engines.

"1, move the breather take off point away from the timing cover or at least move it higher up the cover if, as it appears, there is a potential for a pool of oil in the bottom --" Do you mean when the engine has stopped? Very little potential for oil to pool. Where would it pool? Look at the inside of a timing cover. And moving the breather canister isn't solving the essential question of why it works ok on some(most) A series engines, and not on others.

"2, get a small hole filler cap." Malc did this already.
"3, fit a new PVC" graeme did this already. As did I many moons ago.
"4, Remove the PCV and vent with Y pipe to the carbs" I did this already and there other people in the archives running with the Y piece that also have oil sucking.
"5," defeats the object of the closed system and is less efficient.
"6, on a worn engine, fit a non-vented cap." This happens to FRESHLY built engines too.
"7, recondition the engine and hope for the best ;)" As 6, been done, and didn't solve the riddle.

Paul, as your still on board. Do you -- or anybody else for that matter --- have a picture of the FRONT of a stripped A series block, showing an ORIGINAL fitment of the FRONT cam bearing?

Yes I'm returning to a theme, please humour me.
Lawrence Slater

Bob? I don't suppose you also still have the old pipe you took off do you?

As the weather is now getting cold again, how about refitting the old oil filler cap and pipe, and see if the problem returns?

Or, if someone wants to send me their PCV, I'll fit it to my engine and see if I start sucking oil again. It used to with a PCV, so it should do again.
Lawrence Slater

Sorry, I binned the old pipe. I think it may have been hose which was not oil compatable as it had expanded where it connected to the timing cover and I couldn't get a decent oil tight seal.
Bob Beaumont

Ah well. Just a crazy thought. :).
Lawrence Slater

I will be continuing to watch and participate in this thread and look forward to understanding why this happens...

For reference :-

1275cc Marina engine, with Marina sump (different to Spridget), twin 1 1/4 carbs from 1098cc engine re-jetted to suit 1275cc, car as bought had the early rocker box with non vented cap and bent pipe with restrictor in it, the timing cover pipe vented to air.

On two 2 hour motorway journeys, the car lost circa 2 litres of 20w50 oil (Halfords FWIW) from the dipstick oil, so I got a PCV from a 1968 MGB GT (part number13H5191 - same as a Spridget), cleaned it, checked diaphragm and fitted the PCV to the car.

Started the car up and as the coolant temp lifted of it's stop a large cloud of bright blue smoke burst from the tailpipe, the smoke continued, increasing and decreasing a little throttle related for a period of 2-3 minutes, this happened every time I started the car from cold, no exceptions, on two consecutive days I reached the same point in the road, a left turn halfway up a hill, so I had accelerated up the hill, before lifting off, braking and turning left and downwards, when the cloud appeared.
I checked the PCV after stopping the car on the third time and oil was retained in the PCV.

Further thoughts, as the engine came from Marina and is in a Sprite, I don't know which front plate was used, or if there is difference, I don't know the age of the engine, or it's mileage, it did generate 50HP at the wheels at Peter Burgess's rolling road, with 10HP in the transmission, the original Marina did 61HP when new, but I think had only one carb.

Why do I say this, because I've just decided having the car on the road is more important that understanding the underlying issue, so I've bought and about to fit a catch tank in the timing cover to PCV pipe, because it's only pipework, I will return the car to how it was when I feel the need learn, but at the mo, my Sprite is the main mode of transport and I can't live with the clouds of blue.

The next steps.
I'm going to order a new spring and diaphragm shortly once I've decided whether to stick with the early rocker box or convert to a later one, or go bling and will post what happens then.

Malc Gilliver

what I want to know is did the Sprite run any better with the 'Midget' cap?
Nigel Atkins

Bob: that's an intersting commentabout not getting a decent seal. Doesn't that tie in with MGMike's comment about the pcv not working correctly if there is a lrge hole in the filler cap. Whether the air gets in via the filler cap or a leak in the suction tube, isn't either going to result in a malfunctioning pcv?
GraemeW (Kent!)

That's a shame Malc. Being the only living oil sucking A-series in captivity at the moment, you were my best hope of finding out why it happens, through experimentation. But I quite understand, why you'd rather not drive with clouds of smoke. On the bright side, you'd probably have found that it doesn't happen on warm sunny summer days. So it would only have been for 11 months of the year that you'd have had to suffer the clouds. lol.

I'm guessing the marina engine mounting is different to the Spridgets, and hence you would have a spridget engine front plate.

Now my brain cells are back on this topic again, my thoughts are this.

I don't believe this happens 'at all' to original engines. By that I mean produced in the factory and installed in the cars when built, and then driven until they are worn out. Even when worn, although all engines, including A series smoke, due to worn rings/bores and valve guides/stems, often causing oil to be present on the plugs and on the tail pipe, they don't exhibit this particular set of symptoms. A well worn engine smokes all the time, and consumes oil at a steadyish rate in the same manner.

These particular symptons only occur at specific times and temperatures. From my reading of the 20+ mentions in the archive, and of my own engines, I can say that it happens to SOME engines, AFTER the engines has been rebuilt, and not neccessarily modified with a big valve head and or non standard pistons or camshaft. During the rebuild process, something deviates from the original factory build, when the engines are assembled. Plenty of people have rebuilt these engines, and not all suffer oil sucking. So what happens to some engines during rebuild, that doesn't happen to others?

On my first engine, I had a rebore to 20+, new standard pistons and changed the cam bearings. Prior to that, even though worn and a bit smokey, it didn't suck up oil. After the rebuild, it did suck up oil. But when the engine warmed up, the sucking stopped, it didn't smoke or consume much oil, and had very good compression. I still believe this to be an oil feed/drain issue, into and from the timing cover. Not a case of too much vacuum or blow by. Hence I'd appreciate it, if anyone has a picture of an ORIGINAL FACTORY installed front camshaft bearing installation.
Lawrence Slater

so ... did the Sprite run any better with the 'Midget' cap?
Nigel Atkins

As many of you may know I was one of the "afflicted" and initiated a mega-thread a few weeks ago.
In my case the cause was incorrectly installed oil control rings (Doh!).

I do however have a marina engine and can say that you will have a midget front plate fitted. The marina engine was mounted to the marina directly via the block (which means there are extra bosses cast into the block).
You have also to be aware of two extra bolt holes at the base of the block which need to filled with bolts else oil is splashed out of them when the engine runs (don't ask how I know!!).

I am currently running my engine with the breather venting to air as the PCV I picked up an auction website seems defective. However I have a single HIF44 with a port to the upwind side of the butterfly so I may experiment with that..
T Dafforn

Only just started to read the end of this thread as it didn't seem too interesting until I came across the question of oil filler cap. Many, many, many years ago I had an Austin Allegro Estate in Vermillion and I fitted an MG Metro engine to it. It would be ok until on long high-speed journeys (like going from Manchester to Cornwall fully loaded with wife two kids and camping gear) it would blow oil out of the dipstick hole and past the rocker gasket which would eventually get to the exhaust pipe and create an effect like a warship making smoke. Slow down and it would clear, speed up and it would start again. I only stumbled on the solution after much head scratching. I replaced the black oil filler cap with the red MG one. It never did it again!!!!!! It had the alloy MG rocker cover so it could have been the ordinary black oil cap didn't fit properly but comparing it with a steel rocker cover, I couldn't see any differences to how the oil cap fitted.
MG Moneypit


I get the impression you're waiting for Lawrence to answer ....


Thanks for the update on the Spridget front plate.
A defective PCV - it can only be a new spring or diaphragm to fix it - there isn't anything else in there (unless they have filed it or something really stupid).


I fully appreciate that I'm taking your only way 'field testing' ideas away from you, which was part of the reason to summarise as I did, the other reason, I didn't want another thread where somebody did hours of reading for no end answer, and when I've got the new parts fitted, I'll post if it works or not.

However, I don't believe my engine has been rebuilt, just transplanted, maybe I just need 1 inch thick spacers under the engine mounts and make the oil run away...........

Malc Gilliver

Sorry, no stripped A-series here at present.
Paul Walbran

Were you waiting for an answer from me Nigel? I thought he meant you Malc, I answered earlier just for fun. But anyway, as I said it won't make any difference if I do fit the midget cap. My engine doesn't smoke hot or cold anymore, since I converted to a single HIF.

Malc, I was only joking. I honestly don't expect you to keep your engine smoking just to help me out. Believe me, I know what a pain in the ar*e it is to have that amount of smoke coming out. You really think your engine is still on the original rings/ends? Must be low mileage then. What year did Marina 1300 engines cease production?

Paul, no worries. I just wondered if you had a pic of an OLD installation. Maybe one that you had stripped for rebuild and took a pic before you did it. i can't imagine why you would, but some people photograph this sort of thing. Moi? lol

And just to add fun to the mix, read the following posts, -- in reverse order -- from a 2007 thread. "Crankcase vent sucking oil at moderate rpms" Technical archives.

Posted 31 December 2007 at 18:22:04 UK time
CJ, Titusville, FL,
This is the same conclusion I am coming to. The Timing cover is slowly filling with oil as it is not draining fast enough. My haynes manual shows about a one inch hole in the crankcase up near where the oil separator is. I also think there is a hole under the crankshaft as well. I believe oil come to the timing cover via the camshaft bearings. I am replacing the oil pan gasket after the car sits a day or two. My hope is that maybe I'll be able to see something from inside. Maybe just some liquid gasket blocking the drain. Wishful thinking? Probably.

Posted 31 December 2007 at 10:49:06 UK time
Robin Cohen, Berkshire, United Kingdom
Hi All
My newly built 1275 motor is doing the same, now 1500 miles past the rebuild. I'm convinced that it isn't a ring problem as oil isn't being burned and the compression test looks good. So..I have a new theory..the drain holes that should allow oil from the timing cover to drain back into the crankcase may be blocked up with wellseal? Can anyone remember were the holes are..I seem to remember them being in the main bearing journal?
Can anyone remind me how oil gets to the timing cover/chain in the first place?
The plan is, once I have got all of your comments lift the front of the engine, remove the timing cover and check that oil can freely return from the timing cover as I suspect that I am building oil up in the cover so it eventually fill it to the breather hole and the chain is whipping it.
Happy Xmas to all!

Posted 09 December 2007 at 12:10:05 UK time
C. J. Charvet, Titusville, FL,
I have finally got my '72 midget on the road this week. When I hold the rpms close to 3000, I'm sucking oil from the timing cover breather, through the pcv valve and into the intake. I have heard that after a break in period on a rebuilt motor the crankcase ventilation would balance. Could that be it? To much blowby the new piston rings? I have cleaned the PCV valve and now I need to clean it again. Any help would be much appreciated.

Now who else has been saying similar things I wonder? From what I can tell, the problems were "solved" by disconnecting the breather system. By searching a different way, I've found a dozen more that I didn't find before. This is way more common that it looks. there are posts way back to 1997.
Lawrence Slater


No worries, Marina finished in 1980 according to wikipedia, my car was last taxed in 1979 !!!!

So the engine could have anything from 9 years old to brand new, I'm fairy sure the tin worm took it off the road, not the engine, but I don't know when the engine was swapped - guessing here, he wouldn't have taken if off the the road after just putting a new engine in, so maybe that engine swap was mid 70's.

I bought it in 1992 and taxed it in 2008 - it lurked in my Gran's garage till I got sick of mentally adding to my jobs list !


Just read your posts, as Tim said, my car must have had a front timing change to enable it to fit - maybe it's just some RTV / cheap gasket or similar blocking the drain hole(s).
Malc Gilliver

Missed the post window.

Next time I change the oil, I'll drop the sump, disconnect the timing cover to PCV pipe and pour 20w50 down the vent pipe and see how long it takes to come out the bottom of the engine.
Malc Gilliver

Right, then you may well have an unmolested engine there. That must be pretty rare these days.

Good idea about pouring the oil into the top of the cover too. I did it with the cover off the engine, which didn't really tell me much other than that the oil flows through the wire mesh faster than I expected, even when cold. The wire mesh is only 25mm in depth, most of the canister is empty. If we only knew at what rate the oil was delivered to the timing cover, -- via the camshaft front bearing -- the comparison would reveal a lot.
Lawrence Slater

That's my point, we know oil goes through the gauze, what we don't know is how fast oil drains back from the timing cover.

Once the timing cover has enough oil to cover the gauze, the engine pumping and vacuum will drive the oil up, the only fix is to understand what is stopping it drain in the first place, as the front plate is bolted to the block and timing cover to the plate, it might be that interface doing all the damage.

So pouring oil though the gauze and into the sump, then clearing any holes out might show a large difference in time or nothing at all, but then at least you can measure your engines - even the one out of the car and I can do the same and compare the time taken.
Malc Gilliver

as MG Moneypit pointed out the black plastic cap doesn't fit so well on some of the alloy rocker covers, (some of) the manufacturers and sellers probably want the additional sale of the chrome cap to go with it

sorry Lawrence I missed your answer previously (a lot of posts here)
Nigel Atkins

Nigel. "did the Sprite run any better with the 'Midget' cap?" Actually, thinking on, reverse that and it's a really good test.

Will my 'Midget' run any WORSE with the SPRITE cap?

A lot of argumnent here is going into the idea that too much airflow into the rocker cover, causes the oil sucking. OK. So take a car that doesn't suck oil, and try to make it, by increasing the airflow into it's rocker cover. I know my Sprite used to suck oil, and that the cap has a hole MUCH larger than the "correct" sized hole. I say that I reduced the suction by swapping to a single HIF(Paul disputes this as being possible), and thereby stopped the oil sucking. But there are two 'connected' elements. Suction and airflow in.

My Midget is still on twin SUs. Apart from a standard valved head -- ( maybe that's a key factor? But maybe not, as I didn't always have a big valve head. ) --, it's pretty much the same engine. So I would expect a measure of depression(vacuum) taken at the carb breahter intakes, to be much the same as on my Sprite when it still had twin carbs. Hence if the suction is the same on both my Sprite and my Midget, and I introduce the other variable from my Sprite -- more airflow -- in theory, oil sucking should commence. BUT, only if the oil filler cap is the culpret.

When I get the rad back in the Midget, I'll try it.

Malc, you're now thinking almost like me. If the oil can't drain fast enough, eventually the timing cover will fill and oil sicking commences. However, I very much doubt that your drain holes are blocked. There are 2 of them in the front main cap. (see pic in engine breather thread). They look too small, but it has to be remembered that most engines don't suck oil up, so they must at least be adequate on most A series engines.

The other component is the fill rate. Oil is fed into the timing cover primarily from the front camshaft journal/bearing, with some seaping in from the front main crank bearing/journal. If too much oil is getting into the timing cover, that would in effect make the drain holes too small. The drain holes can't be enlarged without risk of weakening the main cap. So to me, the answer still rests in the oil feed from the front camshaft bearing. I've also wondered if too much oil was coming from the front main cap. However the crank was a fresh grind, the bearing shells were new, and my oil pressure was high(easily 80+ on start up, and not much less when hot).

So I've ruled out the main cap, which leaves the camshaft area. In particular, the set of the front camshaft bearing in the block, and the condition of the camshaft end plate. In the extreme as an example, if the bearing was too large, and the small feed hole in the camshaft endplate was made far larger, that would allow a greater amount of oil into the timing cover. Setting the bearing too far back, is in effect to enlarge it as far as oil flow is concerned, and bending the endplate has the same effect. None of this is proven. Unless someone else finds what I found when I stripped my engine, then it may just be unique to my engine. But what isn't unique, is oil sucking. So there must be an essential common factor present, without which oil sucking can't happen.
Lawrence Slater

Lawrence said:-
"A lot of argumnent here is going into the idea that too much airflow into the rocker cover, causes the oil sucking. OK."

I'm still on board with the pooling in the timing cover until such time as it's proven not to be a problem. If oil pools to the point of covering the breather outlet, breathing will be impossible without sucking the oil up first (or warming to the point it flows better).

I have a stripped Mini A series block in the garage if that helps? (not at home at the mo. so can do pic's Monday if required)

"I say that I reduced the suction by swapping to a single HIF(Paul disputes this as being possible), and thereby stopped the oil sucking."

Were the twins Y and carb vented or manifold and PCV? If the later it doesn't surprise me that it stopped the oil suction as the breather connection on the HIF44 is up stream of the butterfly near the bridge in the carb. The air pressure (depression) at this point is only slightly below atmos and is AFAIK not low enough to lift a column of oil. If the twins are carb vented, I'm with Paul as the pressures should be the same as the HIF unless the filters are restricted/blocked!

"So I would expect a measure of depression(vacuum) taken at the carb breahter intakes, to be much the same as on my Sprite when it still had twin carbs."

Carb vented, yes.

"Hence if the suction is the same on both my Sprite and my Midget, and I introduce the other variable from my Sprite -- more airflow -- in theory, oil sucking should commence. BUT, only if the oil filler cap is the culpret."
All other things being equal of course ;) (like the amount of oil in the timing cover!)

It'll be interesting to try..

Best of....

M McAndrew

I don't suppose that you have modified the oil pressure relief valve in any way on your Sprite have you? It is common practice to use a longer spring or to pack the spring with an extra washer.

Incidentally when I introduced my comment " Too much air in = too much air and oily substances out = blue smoke." I wasn't relating that to sucking up liquid oil, but to the quantity of oil laden fumes being drawn out. I think if or once there is a slug or column or whatever quantity, of liquid oil covering the entrance to the breather pipe, then it really won't take very much suction at all to pull that up the extra couple of inches to deliver it into the induction system. And this is a distinctly different type of process at work.

A large air flow will purge the crankcase fumes faster, but not necessarily involve a greater pressure differential. In fact the opposite might be true. If you install an extractor fan in your garage to get rid of welding or paint fumes you want a good volume of air flow so that it changes the air quickly. You don't want so great a suction that all your tools fly out the vent along with the fumes!

And talking of suction, this is caused by the difference in air pressure between the induction tract (low) and the crankcase. The pressure in the crankcase has to be higher than in the induction tract. Suppose that you draw a graph of the pressure in the crankcase at constant revs (i.e.constant additional pressure pumped in from blow-by) and in the induction manifold whilst altering the oil filler cap air flow rate. With no filler cap the pressure in the crankcase would be at atmospheric, or above, depending on the amount of blow-by minus the induction suction (IS) via the breather. As you then restrict the air flow in by fitting a filler cap with progressively smaller air hole, the pressure in the crankcase will increase at first as it cannot expel air so readily. But this will also increase the pressure differential to the IS so it will begin to suck faster, at least at first. As the air flow is progressively sealed off the crankcase pressure will go up and overwhelm the rate that the IS can cope with.

So I think the size of the air hole in the filler cap is critical to manage the crankcase pressure and the airflow though the system purging the fumes. But I doubt it has any impact on the liquid oil suction, which as I suggest, needs very little IS to achieve.

Guy W

Guy. Nope. Standard length oil pressure relief spring, with no modifications to the plunger. You may have dropped out of the other thread when we had that discussion. But in any event, even if my oil pressure is too high, due to a faulty pressure relief, others also have high oil pressure, and don't suck oil. Still I agree, it's a valid thought because the oil leaves the cam bearing under pressure. It must follow that the higher the pressure, the greater the amount of oil forced out of it.

"I think if or once there is a slug or column or whatever quantity, of liquid oil covering the entrance to the breather pipe, then it really won't take very much suction at all to pull that up the extra couple of inches to deliver it into the induction system." ---- Agreed again, and we've had that discussion before too. The point here is, if it were a slug, it would clear pretty quickly, whereas a large quantity of oil will be burned in the combustion chambers for minutes on end. The visible and audible effects are very obvious. So whilst I agree that all engines can suffer the effects of a build up of oil laden fumes in the breather system, which may or may not happen at certain temperatures, not all engines draw up a continuous column of liquid oil. And it's the latter, that somebody who hasn't experienced it, finds hard to accept as happening. Does a slug of oil, or a mist of oil laden fumes, contain 2/3rds of a pint of oil?

I posted this in the "engine breather thread earlier this year. 20 August 2013 at 14:26:50 UK time
"How much oil sucked up? Where does the 1/3rd pint come from? See my Post 02 March 2012 at 12:49:25 UK time, and look at the picture. I originally fitted that clear pipe in place of the rubber hose to see what was happening when I first experienced oil sucking. I could easily see when that pipe was full of oil. I've still got that pipe on my car. I can see if it's clogged with anything or not, and it's not. The volume of that pipe is enough to hold 1/3rd of a pint of oil when full. I've seen it FULL of oil on NUMEROUS occasions. --Now look at the pics below again. I filled my timing cover today with oil, and then drained it into a pint glass. It too can hold about 1/3rd of a pint of oil. So with my breather pipe full of oil, AND the breather canister full of oil, my engine was being fed a continuous supply of oil from a reservoir of "at least" 2/3rds of a pint of oil. Now you tell me that "mist" in the timing cover condenses to form 2/3rds of a pint, and I say you're wrong. " -- quote from the past ends!.

Present day.
"And talking of suction, --- " I pretty much agree with you, but I'm open to doubt. Earlier I said I doubted the oil filler cap had anything to do with it. But then I saw the difference between my Sprite and midget caps. Then I read the history of the caps and it seems the hole size should be 5/32". Clearly this must have an effect. And yet my Sprite no longer sucks oil even with a bigger hole in the cap. I don't have excess sump pressure, -- as determined by the almost complete lack of rear scroll leak, and I don't have a weak fuel/air mixture requiring me to alter the carb to compensate for it. So I now think that whilst the cap might contribute to the problem, it isn't the cause. Maybe it can tip the balance on an engine near that point though. Maybe that's why it fixed Bob's engine. Honestly though, who amongst us actually knows?

" But I doubt it has any impact on the liquid oil suction, which as I suggest, needs very little IS to achieve. " --- Absolutely I agree. We agreed this before in the long engine thread I think. I've proved this back 20 plus years ago. I put ever smaller restrictions into the CLEAR PLASTIC pipe from the breather canister to the Y piece. I still sucked oil. Less could get through, but the pipe still filled up before the restriction. Once the breather entrance hole on the inside of the timing cover is covered with oil, very little sucking will be required to lift the oil. And the only way the breather canister entrance hole can be fully covered with oil, is if the timing chain cover is full of oil. So it's back to drainage and oil supply again.

But now we're on suction, and having just said that is doesn't need much, if the canister is already overwhelmed, it's a good time to express my thoughts on Graeme's description of what happens on his engine. Somebody else too, whose name I've forgotten, – sorry. Graeme fitted a PCV. Started the engine and it sucked oil. It was a new PCV, and he determined there was nothing wrong with it. His engine sucked oil whilst the car was stationary in the garage. No braking, hence no surge forward of oil in the sump to overcome the drain holes in the main cap. Crucially, it stopped when he let the sump oil level drop below maximum. I've already shown (see picture in "engine breather thread" 22 February 2012 at 18:11:57 UK time" ) that the oil level in the sump at maximum, is only 2.75 inches deep. The sump is 6.5 inches deep, and the drain holes in the front main cap are at 5.5 inches. So how does the oil from the sump at 2.75 inches get pulled into the breather canister? For direct suction, it would need the internal hole in the breather canister to be in contact with the surface of the sump oil, much as you need to insert a straw into the surface of liquid to drink. So what else can lift the surface of the sump oil? It must be the crank paddles. They must lift the oil high enough, to let it get sucked into the timing chain enclosure through the larger hole in the block face. Now I think the timing cover must already be near full for this to matter, otherwise it would simply drain back. The alternative to this, is that the paddles lift the oil high enough to "block" small drain holes in the main cap, and prevent the oil fed from the camshaft returning to the sump. Remember though, this is all at a certain temperature. Once the oil is warm enough, the drains can cope. Now when Graeme first posted about this, it jogged a memory in my mind, that if I didn't keep topping up the sump level, my sucking stopped too. I've since found other posts in the archives describing exactly the same thing.

Mike. You refer to pooling again. Again then, where will it pool? "If oil pools to the point of covering the breather outlet, breathing will be impossible without sucking the oil up first (or warming to the point it flows better)." I can only assume you mean that the timing cover is filling because it's not draining fast enough. There are plenty of pictures of my stripped engine in the "engine breather" thread. I'm avoiding posting many in here, so that the thread can be opened easily by those with slow broadband.

And again, for clarity. My 1st 1275 engine (currently in the Sprite) began life with a PCV connected to the inlet manifold. It sucked oil after a rebuild. So I changed to a Y piece connected to the intakes on the twin SUs. It still sucked oil. The 2nd 1275 engine (currently my partially stripped spare) only ever had the Y piece connection to the twin SU carbs. It sucked oil the whole time I used it after rebuilding it, and partially stripping it several times to find out why. I never did find out why. After over 100 K miles it became my spare, and the 1st engine was rebuilt again and put back in the Sprite, where it is now. It sucked oil. It 'was' the Y piece connection to twin SU's, until I swapped to a single HIF44, connected to the breather in just the same way as with the twins, but of course without a Y piece. It was when I swapped to a single HIF44, that the oil sucking stopped!.

Yup, I said "in theory, oil sucking should commence. BUT, only if the oil filler cap is the culpret." Key there is "theory" , and of course the all else being equal you mention is that no air is getting into the sump from anywhere else, that makes the effect of varying the oil filler cap hole size irrelevant. So where else might air get in? Oil dip stick? Rear scroll?

Guy. You said, -- "As the air flow is progressively sealed off the crankcase pressure will go up and overwhelm the rate that the IS can cope with. " So that too is a good experiment. Seal off the oil filler hole completely, whilst keeping the breather connected, and see what happens. What would you predict?

Lawrence Slater

Too much info in one message! - it makes it impractical to respond to your comments in one session in this format.

1. I just questioned the oil pressure valve for he reason you surmise - the possibility of this delivering too much oil to the chaincase, too fast. Especially when cold. But I understand you have covered and discounted that possibility. End of.

2. I wasn't commenting on whether it was a "slug" or a continuous column. I have absolutely no problem at all with your contention of your (and some other) cars drawing up a continuous column of oil. I am not disputing that! The point I was making is that the amount of suction required to lift oil, once it has entered the mouth of the breather system, to the carb or manifold is very little. 1 bar , or just 14/bs/sq inch will lift mercury 29 inches, or water 34 feet. I don't know what the figure for oil is but based on density it is going to be about 20% greater, so maybe up towards 40 feet. So very little pressure differential is needed to lift the oil those couple of inches!

So, in this respect I doubt if the size of the air hole in the breather does actually contributes to the liquid oil problem. But it may still contribute to cars blowing blue smoke screens when it isn't being caused by drawing up liquid oil.

3. If liquid oil can be lifted the couple of inches up the breather pipe with so little suction, then I think variations in crankcase pressure, whether caused by blow-by (engine wear) or the size of the breather cap hole, have little etc. do with it and can almost certainly be ignored. This leaves the only relevant area as the oil level in the chaincase, and what causes that to be too high.

4. Two aspects that I still think haven't been quantified. The first is that we are all using subjective terms for the symptom of a HUGHE blue cloud. I think it is common knowledge, and easily demonstrated, that it doesn't take a lot of oil to make a huge dense blue cloud of oil smoke. A few cc's will do it. And so will several 100 cc's. So not all thick blue clouds of smoke are necessarily caused by drawing up liquid oil. Some will be, and some will be caused by lesser quantities. This will only add to the complexity in trying to identify a single set of circumstances to explain the symptom.

- and the second aspect? - The same symptoms may have more than one cause!
Guy W

Guy. Replying to two people in same post, and adding additional thoughts as they were linked to suction. I wasn't expecting reply to all comments. Thinking as I'm writing, crystalises my thoughts.

On your point 4, I was thinking exactly that, but came to a different conclusion. The opposite in fact. Most if not all posters here, are intelligent and rational people, not given over to exageration. I been scanning the archives for anything related to this subject, and when the smoke is most likely due to a mist, or a puff, or worn rings valve guides etc, then the descriptions indicate that. What stands out when you find a post that describes "huge" or "dense" "clouds" of smoke, is that 99.9% of the time, those adjectives are used hand in glove with other comments. Such as, " only happens just as the engine warms up", and often "if I let the sump level drop, and "pulled off pipe and it was dripping with oil", and "engine doesn't burn oil or smoke at any other time, etc. There are many many many more posts that are clearly smoking engines, sometimes worse when cold, that smoke to some degree all the time, but clearly not in the same category as those described as "massive" cloud of smoke, that "lasts for over 2 minutes and then stops completely". If I can get my Sprite to do this again, I'll video it. Better still, I'll invite you down to see for yourself. LOL.
Lawrence Slater

0Lawrence. I don't need to see your car perform these symptoms. I don't doubt your many and repeated descriptions. It doesn't change the basic fact that almost by definition, until you have resolved the cause, you cannot be sure that all similar symptoms are the result of the same cause. ;-
Guy W

Lawrence, yes you assume correctly ;) I was referring to pooling in the timing cover as a result of not draining away quickly enough.

Thanks for the clarity notes on our config's.

I'm surprised the change to HIF "fixed" the problem as the pressure at the breather points should be the same. I guess determining the differences is another area for further consideration.

Best of....
M McAndrew

Something you guys are over looking

Air filter design

What air filter design are you guys employing

If its the factory trumpet design .... you probably wont have much of an issue with sucking up oil

If your using the moss cheapo 1inch tall pancake design with the foam filter thats going to suck some serious oil

A K&N with a 3 inch tall filter...probably not so much

What im talking about is constriction ....the more constriction you have at the venturi of the carb, (mouth), the more vacume your going to produce,

Think of a shop vac... the busness end is about 3inches in diameter... and produces a certian amount of SUCK... IF you reduce the 3inch diameter to only 1inch....what are the results...

1. the same amount of suction
2. less suction

Anyway, just doing my part to see this thur 400

Prop and the Blackhole Midget

Guy, people have been convicted and hung on less circumstantial evidence than appears here about oil sucking. lol. Granted, a lot were innocent :-. But seriously, having seen it first hand, and had precisely the same form of words enter my mind as way to explain it to others, I'm convinced that there is at least one other person with the same problem that my engine has, somewhere amongst the many descriptions in the archives. And if there's one, there's likely to be more.

Mike. The clarity notes were only on the config of MY 1275 engines, not other peoples.

I say fixed, because it doesn't suck oil any more, and the only thing I changed to make that happen was take of the twins and put on a single HIF SU. Coincidently, without my knowing it, something else may have changed within the engine on the same day. What could that be? ;). Seriously, I did nothing else, so it seems reasonable to me that something about the suction changed, I assume it lessened. As you say, it needs testing to confirm it, and it's one of the things I intend to do. When I get the Midget running again, I'm going to fit my vacuum gauge and measure the depression on the y Piece. Then I'll measure the take off on the HIF and compare the two. Maybe the figures are quoted somehwere if someone has an SU design manual. I used to have a Haynes manual dedicated to SU carbs, but lost it somewhere.

You said "I have a stripped Mini A series block in the garage if that helps?" Doh, I've just re-read that --- . Would you know if the cam bearings are the original factory fitted bearings. I doubt they are after all this time, but it would be very useful if they were to be. Earlier I asked if Paul or anyone else had a stripped block to take a pic of the front camshaft bearing. If your block still has the bearings in it, could you take a pic from inside the block, and from the front at an angle, to show how far in from the front face of the block the cam bearing is inserted?

Prop, way back, one of the first things I wondered was if the KN filters I fitted cause the problem, so I put the original pancakes back on. No change. Still sucked oil. But I agree, if suction is the prime cause, maybe air filters make a difference too.

I'm vacillating on the suction question. In one breath I agree it can't be the "x" factor, and then in another I argue that it was the deciding factor in stopping my engine sucking oil when I changed to an HIF. Like I said before, nobody knows really what's going on here, only that something's going on.

I've read so many threads in the archives now, I'm coming over all Lady GaGa( - careful how you read that lol). Anyway, yesterday I read one somewhere -- or was it in this thread -- that just as the big blue cloud started, there was a drop in oil pressure -- 10psi?. was that you Malc, or was it in the archives? The point is, why would the oil pressure drop like that? Maybe so much oil is in motion in the crankcase, and so much retained in the timing cover at the point, that the sump oil reservoir drops momentarily, below the mesh covered tube to the oil pump, and starves the pump for a moment. Or it could be that the poster got it wrong, and the two events aren't connected at all.

Lawrence Slater

Just thinking....

What about engine rings and dip stick holder

If there is alot of slop and wear in the dip stick holder and the dip stick plus worn rings and push rod lifters

could that not create a situation that would.allow oil to move around much easier with less vacume then when was new

My thinking if there is no wear, and a vacume applied, wouldnt the oil be held in place...or would it be severally forced out any type of hole available

I still think untill a vacume gauge is applied, and we know what the facts are this whole argument is purly conjecture and academic at best....

15 psi vacume vs 4 psi positive pressure are going to be 2 sperate issues causing the same problem

Prop and the Blackhole Midget

Why not cut a whole in the timing cover add a window and check out the situation. I think the next best thing was already discussed, Clear tubing!
Steven Devine


I didn't mention any drop in oil pressure, something else to look for.


FWIW, I have standard air filters inside the original 'saucepan' air filter cans.


Lawrence is already considering a plastic window in the timing cover.


"Onwards to 400 posts and beyond " - lol
Malc Gilliver

I know this is an A series problem but ..... I still can't find anywhere anyone asked to check for excessive blow by and therefore higher crank case pressure. Are we all assuming the basic workings of the pistons and rings is correct?
All my 1300 marina engines (3) and 1300 mini (2) and Austin 1300 (1) engines of the 70s just ran (often up to just over 100,000 miles before burning oil) with no oil burning at all if nothing went wrong on standard set up.
They were all piston related failings. Rings worn out. Uneconomic repair at the time.
Dave Squire

I think the common worn rings problem of a trail of blue smoke is a different type of symptom to the one that Lawrence is perusing. The worn rings create a continual discharge of blue, often worse on overrun if the breather system connects to the manifold rather than the carbs. This different type of blue smoke discharge is sudden, relatively short lived and very dramatic!

Overfilling of the chaincase does seem to me to be the root cause. And I have no doubt that this occurs when a number of factors all come together to combine the effect. If those factors are "out of synch" it probably doesn't occur which may explain the relative rarity.

The bit that does puzzle me though is Lawrence's experience that changing to a HIF carb cured it. For the reasons I listed earlier I just don't see how the amount of suction really should impact on the scenario of pulling a solid column of oil up the breather pipe. It needs so little suction to lift the oil. 1bar (14.5psi) will lift a light engineering oil nearly 40 feet. OK, 20/50 may not lift quite that high,and would certainly be slower to lift that high, but one is still measuring the lift of a couple of inches, in the order of less than 1psi difference between crankcase and the suction end of the pipe to draw the oil through the pipe.

Where I do think that blowby and the amount of pressure differential is important is in the different oil burning condition where it is dependant on the volume of oil vapour laden air being pulled through the breather. This can be simulated (and sometimes inadvertently is) by connecting the breather pipe direct to the manifold without a PCV valve. But as Lawrence will insist, this is not the oil burn problem he is investigating. And it is also the reason that I keep saying that not all subjectively described similar symptoms have the same cause.
Guy W

Yes Guy,

I strongly agree <'And it is also the reason that I keep saying that not all subjectively described similar symptoms have the same cause'>. Just like for instance lung cancer is more likely due to smoking but is not necessarily caused by smoking.

We need to concentrate on Malc and his specific problem in his specific scenario as its causes may vary wildly even though the actual resulting behaviour may be similar to someone else's. Otherwise it becomes totally confusing. :-(

Dave Squire

Thanks for the update Malc. Ill have to keep an Eye out for how it plays out. Amazing an issue like this would plague a car for so many years with out a real solution.

Props going to add a kitchen sink in to the plumbing problem just to have some thing to bla bla bla about!
He really needs to just go take a vid of his car to proove its really running! Yes captian jack wagon! Go do the vid and stop being the MG Einstien for 24hrs!
Ha ha ha!

Anyway it will be fun to see what comes of this. Who knows! Prop may figuire it out 24hrs from now!
Steven Devine


Checked the oil and topped up to maximum.

I fitted a 1 litre catch tank, because it had a drain fitted at the bottom, I needed to fit it with access so I mounted it on the drivers side in the well under the steering rack and then added long pipes that go from the timing cover over the engine and into the catch tank , then back over the engine to the PCV.

Started the car from cold, drove until the car warmed up - NO SMOKE, however, when I got back I checked the sight glass on the catch tank - it had over 0.5 litre of oil in it !

Then I checked the cylinder pressures.

cyl 1 - 125psi
cyl 2 - 115 psi
cyl 3 - 125 psi
cyl 4 - 120 psi

next job, drain the oil from the catch tank - I am happy I picked a easy drain location !! Then run the car tomorrow and see what happens - I'll keep the oil that came out of the catch tank, but not put it back in case I have found the engines preferred oil height.

Having confirmed I have a Marina sump - any ideas how much oil a Marina should have it in ?

Malc Gilliver

Steve, I've already got a clear plastic tube as a breather hose, and have had for 25 years, precisely to enable me to see the tube fill with oil.

Note for those who keep mentioning worn rings etc. Many posters, inlcuding me, experience this problem AFTER a rebuid. Often a rebuild, using new pistons valves crank etc. If this is due to a wear problem, then it's an obsure item, possibly one not changed in a conventional rebuild.

Dave. Malcs problem isn't unique. It's related to at least 2 dozen threads in the archives. Malc uses a PCV. My experience began in exactly the same way. And, "on the same engine", I tried to fix the problem by converting to a Y piece breather system. That didn't fix the problem. The descriptions Malc give, match my own experiences -- 1st reported here in 1998 --, exactly. So I think it worth considering all the evidence from anywhere, confusing though it may be.

Guy. my HIF conversion baffles me too. If as you and others say, there is very little difference in suction between a Y piece and a single HIF, then how did my problem go away? I did mention way back in the "engine breather" thread that the only other possible thing to change could have been the bedding in of my cords rings, but the abrubt end to my oil sucking, when I swapped to an HIF, kind of excluded that. I can't help but come back to one central theme though. An overfull timing cover. If as I believe, for a small period of time as the engine warms up(or cools for that matter), the oil level covers the breather entrance hole, then oil sucking becomes almost inevitable, even with a low level of suction. Maybe a lot of a-series engines are on the brink, but not quite over it. Maybe it's just a minute difference in the oil sucking engines, that causes the oil to get sucked up.

No suction, and no oil sucking. When my engines were doing this, I too tried the "leave the breather hose open" solution. With the canister vented to air, I could smell the oil fumes, and got a rear scroll leak. But I didn't get oil being pumped out of the open breather hose. So clearly, no matter how much oil was in my timing cover, crank pressure alone wasn't enough to push it out of the timing cover. Apply suction though, and it would recommence.

There is really only one way that this is going to be resolved. We need an engine sucking oil, to be used as a test bed. To that end I'm going to try and make my Sprite suck oil again. When I get around to it, whilst the weather is cold, I'm going to reinstall my twin carbs. If that fails, I'll put my spare engine back together as it is, with the same rings, shells and everything else. That never stopped sucking oil, so hopefully I can use that as a test rig. I'm thinking of sticking it in the Midget. That way I can keep my Sprite on the road for use.

I'll use long lengths of radiator diameter hose, so I can connect the rad in the cowl with an electric fan, to sit off the car, to give visual access to front of the engine. Cut the front out of my spare timing cover and see if it reveals anything.

Lawrence Slater

Malc, that's a lot of oil. 0.8 of a pint. I've already measure my breather hose alone as containing 1/3rd of a pint. So you've confirmed imo, that the timing cover was full, and that you sucked up a continous column of liquid oil.

Can you confirm your catch tank setup? I'm assuming it was a sealed vessel that maintained the manifold suction from the PCV. So therefore, once the air in the catch tank had been evacuated, it was essentially no different in effect to having just the pipe in place. But the crucial difference was that under gravity, the oil had somewhere else to go, other than into the PCV/manifold. It follows then, that if the right conditions continued (cold engine/oil) the tank would have filled up, and would have acted as a reservoir for 1Ltr of oil being fed directly into the manifold. Which is what I've been saying is happening for years.
Lawrence Slater

I have a spare Marina 1300 sump and comparing it with a Spridget one the only difference I can see is the plate welded on the bottom of the Marina sump, I presume to bolt to the gearbox. Apart form that it is identical in all other dimensions.
Bob Beaumont

6.5 pints(inc filter) of oil in the sump according to a marina w/s manual.

Lawrence Slater

In case it's useful. Marina downloads from here.
Lawrence Slater

Your comp readings are pretty close to each other, so doubt any broken rings there.

Marina 1300 compresion ratios are. LC 8:1 HC 8.8:1

So for an LC engine probably good compresion readings, but for an HC engine maybe a bit low. Does it smoke and burn oil at other times? You know you have blowby because of the oil from the dip-stick hole, but is it enough to "blow" the oil in sufficient amounts into the timing cover, or prevent draining back into the sump?

I've speculated this before. If there's suficient +VE crank pressure, "pushing" against the oil as it tries to drain back thorugh the small main cap drain holes, at the same time as suction is "pulling" on the oil from the other side, that might be enough when the oil is cold, to prevent the timing cover draining fast enough.

But if that were the single cause, then ALL worn engines would start to suck oil, so there must be another factor(s) at play in addition.
Lawrence Slater

I read you did the plastic tube and made the hole diameter smaller. I see you have been around the block literally with these engines... Ha ha ha!

I hope with all your experimentation you get a confirmable answer. I like prop love the chase of stuff like this, Its fun to see what makes these issues happen. I wish you luck in a solution!

I havent enough experience with the A series to have seen this particular issue.
Steven Devine

Catch Tank Setup

The catch is one litre volume, the bottom of it accessible from below, as it has a bolt to drain it.

So it sits a few inches below the steering rack.


Malc Gilliver

<<Guy. my HIF conversion baffles me too. If as you and others say, there is very little difference in suction between a Y piece and a single HIF>>

I didn't actually say that. I have no idea what the comparable figures are. What I was saying is that as so little suction is needed to lift the oil through the breather tube, once the lower end if flooded, it cannot make any real difference whether its a Y connection or an HIF connection. Just about ANY amount of suction will do.

I do agree the flooding oil version of blue smoke must be because the chaincase floods. And that this is likely to be a combination of factors coming together.

I wonder if the variable that makes it appear to happen on some engines and not on others is to do with where people live? Serious comment!

If in order for the chaincase to fill it needs a good oil flow in (e.g. reconditioned engine, new pump, viscous fresh oil) running with engine at moderate to high revs whilst engine oil is still cold (e.g. suitable fastish road near to home/ journey start, maybe dropping down a gear/ raising revs, slowing for a roundabout).

I don't agree with the suggestion that crankcase pressure will slow oil drainage back through by the lower bearing holes. But oil viscosity certainly will. I don't think there is ever going to be much pressure difference between crankcase and chaincase because of the size of the interconnecting "window" hole. If it were just a small hole it could result in different pressures, but at the size it is, it will allow the pressures to equalise too fast.

I did once have this happen on a Maestro Turbo. Thought I had blown the turbo. Massive smoke screen for 1/3 mile, which then just as suddenly cleared!
Guy W


I've experienced excessive blow-by and oil being blown out the breather pipes into a catch tank but that was due to a new build with new bores, rings, and pistons. things quickly settled down and after 100 miles no more problems of blowing large amounts of oil out, just some fine mist. The engine had about 65k miles on it when last the head came off and the bores looked in great condition. The other end of the scale would be excessively worn rings leading to excessive blow-by. What was the result of any checking of the state of your rings on the afflicted engine.
David Billington


in the photo it shows still on (what looks like to me) a non-vented cap, have you tried this set up with the (less effective than plastic) bling chrome vented cap
Nigel Atkins

David, The rings are still in the bores. But, it sucked oil from day 1, and did 100k plus miles, without a problem other than the cold/warm up oil sucking.

Guy, oil sucking can and does happen just warming the engine on the drive.

Malc. Apart from having to empty the tank each time you go for a drive, you've got a solution there. ;).

But this is good stuff. Now you've demonstrated the amount of oil pulled up, I hope speculation about if it is really happening will cease, and concentration on how it is happening will take it's place.

And just to clear up my HIF mystery, here are my results.

At a steady 3000rpm, my vacuum gauge reads 0 INS Hg, connected to the BREATHER PIPE TAKE OFF on the carb. If I floor the throttle quickly, I can just barely make 1 INS Hg.

At a steady 3000rpm, my vacuum gauge reads 20 INS Hg, connected to the inlet manifold.
At a steady 3000rpm, my vacuum gauge reads 20 INS Hg, connected to the advance/retard take off on the carb.

So I was spot on. Connecting my HIF instead of the twin SUs, dropped the suction -- out of sight--, and stopped my engine sucking oil. Clearly there's a problem with my HIF, I'm sure it should be a higher reading than that. But whatever it should be, it confirms to me at least, that suction is a vital component in this as well as something else, which I believe to be the fill/drain rate in the timing cover.
Lawrence Slater

Interesting. I have a very similar spec engine to yours Lawrence. wonder what suction I would get on my HIF. I wonder if I can rig something up to test mine. What gauge were you using?

Zero suction at the HIF cannot be right. Are you sure you are testing the correct connection, and not the carb overflow !!

The 20" Hg at the manifold isn't at all surprising. But you wouldn't connect a breather direct to the manifold anyway. And it doesn't tell us what the suction at a Y piece connected to twin SU's is.

<<I hope speculation about if it is really happening will cease>> I wasn't aware there was any such speculation !
Guy W

these are exactly as I would expect. Both the manifold and advance take off are on the same side of the throttle butterfly and should be the same pressure (as you have). The breather is up stream of the butterfly and should be near or fractionally below atmos, just as you have measured.
Now you need to see what the readings are with the twin set up and Y pipe. These are the ones I have an issue with as they should be the same as the HIF.

best of....

M McAndrew

PS. 1Bar = 29.53 inHg.

Yup Mike, I already knew that the manifold and advance/retard would be circa those figures. But I'm surprised the breather take off is so low. At any rate, it confirms what I said, the suction lessened from that of the twins. Why I don't know. -- Yet. I'll get the midget started tomorrow and measure the Y piece on that.

I thought there was speculation, in the sense that I was saying the descriptions indicated to me a column of liquid oil, whilst some thought not.

My first momentary thought was have I got the connection wrong, but I've checked that so many times before and even posted the pics on here, I know it's correct. The fuel overflow is open to air. If I leave my breather take off open, the engine stalls at tickover. I suspect an air leak, and yet I don't notice that in engine performance, I'm not running weak, and haven't got the mixture screw in to compensate. Odd. I'll have a closer look tomorrow.

My gauge is a smiths 0-30 ins/hg as below from a previous post.

Lawrence Slater

great set up. We should be able to prove a fix without the expense of shed loads of oil out the back!

Do you know if, when vented to air as originally set up, oil was flowing out the pipe and all over the floor(pan) etc?

I think the next thing to do is to prove the PCV is actually closing when vacuum is applied. Have you been able to confirm that?
I can't tell from the pic, have you blocked the tube going in to the rocker? This will restrict the amount of air entering the engine and should hopefully create a bit of crank case -ve pressure to ensure the PCV closes. I might produce too much and prevent it opening at cruise speeds as intended but I doubt it if blow by is present.

Best of.....
M McAndrew

Mike, both of those questions were answered way back. The pipe's blocked, and there was no flow of oil from the pipe when vented to air.

Do you have a pic of the cam bearings on your stripped engine?
Lawrence Slater

So you just ran a temporary pipe connection from your gauge, behind the dash through to the HIF breather connection? Somewhere in the garage I have a gauge so tomorrow I can try it connected to my HIF by way of a comparison.
Guy W

Lawrence wrote:-
"The fuel overflow is open to air."
I don't understand the relevance of this in this discussion.
"If I leave my breather take off open, the engine stalls at tickover."
That makes sense as it allows a large amount of air to enter the carb thereby reducing the amount of air crossing the bridge to collect fuel ie a very weak mixture.
"I suspect an air leak"
Sorry you've lost me here. An open breather is an air leak!
"and yet I don't notice that in engine performance,"
You won't when the breather is connected and the carb is drawing only a small amount from the crankcase when it's produces a limited +ve pressure from blow-by.

Best of....
M McAndrew

Mike, what I said was all in the context of answering Guy's question, then it makes sense.

Guy, my guage is usually connected to the manifold, I just pulled off the rubber vacuum hose and moved it around the various points, whilst blocking off the manifold connection. I used an adapter pipe to make it fit the breather connection on the HIF.

OH and btw, for what it's worth, I can suck 15 ins hg with my gob, so I bet I could suck up a fair amount of oil. lol.
Lawrence Slater

Dedication to science. Lawrence. Sucking in 15" of mercury could quickly turn you into a Mad Hatter!
Guy W

Yup. luckily it was only simulated on a gauge. lol.

Frustrating. All the descruiptions of SUs say they are a constant depression carb, but nobody quotes a figure for the depression. Mike you say just below atmosphere, have you got a manual in that quotes that, and how much below atmosphere?
Lawrence Slater

Lawerance has nailed in my view

Im sorry ...but if you have only an avg cly psi of 120psi....

This engine is worn surprised this engine can even run

If there is only 120 psi then you have serious blow by which is pressurizing the crankcase... then you your evac is hooked up to the manifold sucking alotnof vacume

Until you rebuild this worn out vent atmosphere, and use a catch tank for the oil

Anything you do beyound a rebuild is a waste off money and time

Im guessing this is the reason For the resistance in using a pressure/vacume gauge in order to NOT confirm what was suspected

The key to this...the the oil BLOWING OUT the dip stick holder....if there is a vac, in the crank case... you wont have oil shooting out the dip stick holder

new rings with a cly hone, and a valve face/seat regrind is a minimum.

Prop and the Blackhole Midget

Another glaring problem I saw in your above photo

The oil filter is in the completely wrong location...

That could well contribute to many of your problems

Can you explain why the oil filter is hooked up to the exit part of the oil galley that goes directly to the oil pump...aka, where the oil pressure gauge goes to

I dont think the oil is able to be filtered (or not well) if the filter is upside down and at a 60 degree sideways angle


Prop and the Blackhole Midget


Pic's for you...
Can't confirm if teh Bearing is original but it's in such a S**t state it could well be.

Best of...


M McAndrew


M McAndrew

Nigel, Mike and Lawrence.

The picture I provided is exactly how I'm running at the mo.

For clarity, I have unblocked the vent pipe on the rocker and returned to non-vented cap (as Nigel spotted) and the vent pipe - which does have some sort of reduction in it - ie it's not the full diameter, I'll confirm how large the reduction is when I remove the rocker box.


It's an engine from a Morris Marina engine, the location of the oil filter is what defiines it as a Marina engine, along with the unique thread that the oil filter takes.

A Marina was a lower power variant only 61HP from a 1275ccm not the 65HP Spridgets get.

I posted the cylinder pressures because I don't know what the number should be.

Malc Gilliver

The above is the oil filter location of malc engine...I think this has to give creadance to how oil is pooling in the timing cover

My guess....its a combination of the 3 below

1.Bad / wrong oil filter location

2. To much vacume

3. Postitive crankcase pressure due to worn out engine 120 psi cly on avg

My theroy without any facts ....

Oil pooling in timing cover because of wrong oil filter location, plus worn out engine producing lots of positive crank case pressure fighting agianst a large amount of vacume do to a bad PVC hooked up to the intake manifold

I think once the cly pressure drops to 105 - 110 psi... the engine will cease to fire and this whole thread is moot


Prop and the Blackhole Midget

Mike, thanks v/much for those pictures. They contrast with my engine(s) in that my front camshaft bearing is recessed into the block, and protrudes inside the block, almost enough to obsure the follower hole. This means that a portion of the front of my camshaft journal, is running out of the bearing, and therefore not containg the oil. I've thought for a long time that this is significant, and seeing your cam bearing makes me think even more, that at least on my engines, my cam bearings weren't installed properly when renewed.

I won't post them again here, but if you look in the technical archive thread "engine breather", 20 February 2012 at 17:38:15 UK time, you'll see a pic of one of my engines camshaft bearing.

Prop, the oil filter location is nothing to do with it. This happens on Spridget blocks too.
Lawrence Slater

Wow....if that oil location andits postioning is correct

I dont know what to say....I cant wrap my mind around that

I have to think thats an issue

It seems like the oil filter should be located on the next oil hole beside it, that the oil pipe comes out of to the midget oil filter...not the oil pressure gauge hole

Plus the upside down and caddy wonk angle of the oil filter looks like it would make the function of an oil filter really inefficient

As to the cly psi... 165 psi is normal/avg is my understanding for a stock engine

On my high performance 1275 last week I measured 215 psi across all 4 cly

Prop and the Blackhole Midget

as you know I have no technical or mechanical knowledge but I think you need with using the PVC to to block off the rocker cover pipe and fit a vented cap

the non-vented cap was used when the rocker cover pipe went to the front carb air filter pan

your engine set up sounds nearer the early 1275 with the oil separator on the timing cover going to the PVC with a vented oil filler cap fitted

that rocker cover pipe should not be in your set up so it needs blocking off for now (or ever)
Nigel Atkins

SU as constant depression caburettor - the amount of depression will depend on the spring in the dashpot. However, it's not much. The big pressure drop takes place at the throttle plate.
Paul Walbran

you're correct in saying it's more a kin to the 1275 set-up. However, if the amount of air allowed in to the rocker is controlled it doesn't much matter how it gets in. I see the non-vented cap and the pipe as an opportunity to implement a variable control on the amount of air allowed in. Controlling the input ie reducing the pipe size to create a -ve crankcase pressure in a worn engine, even if it results in blocking the pipe altogether, has the advantage of making the PCV work as intended.

If Malc had a vacuum gauge on the input to the PCV we would be in a better position to determine if it is in fact working as intended and if increasing/restricting the flow makes any difference.

Over to you Malc.....

Thanks for the confirmation on the constant depression point.
John Twist explains how this happens in his videos much better than I can on here but the end result is as I've said above; the pressure at the breather inlet point on later carbs is not much lower than atmos.

Over to you Lawrence to do some vac checks on your twins....

Best of...
M McAndrew

using the rocker cover pipe as the restriction would take some working out especially as it's already restricted inside

be easier to just completely block it off and then get the vented cap and block off 50% of each hole (or 100% of one hole) and see what happens - if necessary you can enlarge the holes from their original size, if you oversized then you can plug the extraneous hole and if required drill a smaller hole

currently the caps have two rectangular holes 3mm x 8mm (very approx) BUT these apertures have the folded over rolled wire mesh right up against them restricting the air flow but by what amount? by the time you converted this into exactly how much to put in the pipe you could have restricted the holes in the cap and run the first test
Nigel Atkins

Out of interest, and unsurprisingly, I have found some new valves are not spec. Two things: One, the spring clip on the lid doesn't exert enough downwards pressure. Result is that the diaphragm doesn't seal on the valve body so air leaks in underneath. This prevents enough pressure difference for the valve to close under low manifold pressures.

Second, (and I don't have one here to confirm) I have my suspicions about the spring strength - if it is too strong the valve also won't work as intended.

This latter one is only a suspicion, the first abservation is definite. Tried it by sucking through the valve. And when the valve doesn't close under low manifold pressure oil gets sucked up into the manifold and clouds of smoke result - not just in a 1275, but also a B. However, from what I understand of the symptoms Lawrence and others have reported, this is a different issue again. It wouldn't explain for example why breather into carbs cause it in A series but not B series.
Paul Walbran

we'll agree to disagree on this one ;)

I think it would very simple to hook up a plumbing fitting (service valve) and a bit of hose to the pipe on the rocker to provide 100% control of the airflow.
Then, if the PCV is working as intended, it should be possible to close the valve to the point where the breather system operates correctly. This always assuming there isn't way too much blow-by. If there is then no amount of hole blocking is going to reduce the amount of +ve crank pressure and a PCV system is not the solution.

Thanks for the observations. I agree the quality of components in the PCV are critical to its correct operation. Whilst we talk about this valve being open or closed depending on the amount of vacuum, it's actually a very finely tuned flutter valve at a particular pressure differential. I think this flutter occurs around or just above the idle point and therefore it's very important for both tuning and oil sucking that it works correctly.

I think it's time to get the vac gauge out for more testing....

Best of....

M McAndrew


Prop suggested vacuum gauges a number of posts ago, while I remained focused on having a driveable car, now I have the catch tank and clearly still have the oil intake problem, at least I can drive the car without the added cloud.

Adding a variable restrictor to the rocker 'in' pipe is easy enough and then I'm going to need to add vac gauges to other sections of pipe to build up a definite picture.


My PCV is from a 1968 MGB GT, that I broke up and turned into a kit car in 1987, the GT was a a complete wreck and must have been off the road for a number of years, so the PCV assembly could have been original BMC fitment, i checked the diaphragm for leaks, but can't check the spring, but a vac gauge should do that.

I'll have a look at the cylinder pressures today, I feel, as Prop does they are low, but this engine produces 60 of it's original 61HP and the car will do 90MPH and it doesn't (with the PCV off, burn oil)

Malc Gilliver

That's what I've been saying Malc. Piston blow by isn't the cause of this.

Paul, Mike. Yup accepted and known that the carbs are lower depression than at the manifold. But what surprised me was that I could barely get a reading on my vacuum gauge. As I said, flooring the throttle quickly,(beating the piston rise) just manages to make the needle jump, but at all constant openings, the needle doesn't register. There simply isn't enough suck at that point on my HIF, to act as a breather for the crankcase. If I leave the breather open, it stalls the engine, so obviously it draws air, but not enough for PC ventilation.

Just below atmospheric. Yup, but how much precisely? This surely must be quoted somewhere.

And compared to my Twin SUs, the HIF on my engine at least, MUST be lower, for the simple fact that the Twins sucked oil and the HIF doesn't.

As you said Mike, I need to get a reading on the Y piece for Twin SUs. But we also need to know the "quoted" depression figure at the input to the PCV -- i.e. from the timing cover. Clearly too much and oil gets sucked, too little and no ventilation. Obviously Malcs is too high, so it seems something is causing the valve to stay open when the vacuum exceeds an acceptable reading. But what is that acceptable reading?

And even if the reading is correct, maybe it won't prevent oil sucking anyway, because the timing cover is filled with oil.

The two systems (PCV or Carb) are related, in that they both do the same job. The Carb method is a simpler system, but to do the same job, it must have been designed with a comparable depression figure, else it wouldn't work. If the PCV can be faulty in some way, and result in too high a vacuum, it's hard to see how the depression on the Ywin SUs could be too high, esp' since on the HIF, it's almost ZERO. Hence there still must be an underlying cause to this.
Lawrence Slater

Mike we don't fully disagree but also don't fully agree

I did understand what you meant by fitting a variable valve to the rocker cover pipe but I assumed that as it'd be ugly that it'd only be fitted for testing and didn't see how you'd then transfer the info you have to calculate the aperture/airflow required on a much neater permanently fitted vented filler cap

different strokes for different folks

how much or well the PCV works throws in more possible variables

I hope this gets sorted or at least improved and it'll be interesting to see what helps
Nigel Atkins

I put the rad back in the Midget, started it up, and tested the vacuum at the twin carbs. The good news, as just reported in my radiator draining thread, is that my copper radiator cross/drain pipe works a treat. :).

The not so good news is, that the vacuum test on my Midget twin carbs is less conclusive. I've come to the conclusion my smiths vacuum gauge -- which is pretty old -- isn't as sensitive as it should be around the zero mark. Hence I can't say definitively what the reading is. However, I can say that the needle definitely deflects off the zero mark, and is held there. which contrasted with the HIF on the Sprite, which read nothing.

I disconnected the hose from the timing cover to the Y piece, and using an adapter connected the vacuum gauge to the tail of the Y piece. According to my gauge, I got circa 0.5 ins hg of vacuum. At least it does read something, whereas my HIF on the Sprite registered nothing, and the needle remained on it's stop.

On the Midget, opening the throttle quickly, raised the needle above 1.5 ins/hg, and increasing the revs more steadily, once the pistons have settled, raised it a bit more. But clearly way less than the readings at the mainfold. Using a piece of tissue paper as a test on the open Y piece, the paper is grabbed fairly strongly.

I then reconected the gauge to the Sprite HIF and confirmed yesterdays test. The HIF on the Sprite is sucking less than the twins on the Midget, but as my gauge may not be accurate, I have no idea by how much. I guess what I need to do is put my twin SUs back on the Sprite and test those, since it was with those that I sucked oil. But anyway, what this tells me is that the PCV must allow a similar amount of suction on the timing cover, to the Y piece, and as has already been speculated, that is a low figure. For whatever reason my HIF is sucking even lower than that, so that must be why I'm not sucking oil, since nothing else in the engine has changed.

Guy, did you get a reading off your HIF?
Lawrence Slater

Ah ha. Found two bits of text quoting a value for vacuum in a PCVentialtion system. Different contexts, but similar figure.

Found this description of the operation of a typical PCV on Wiki.
With a lower level of vacuum, the spring returns the cone to the "open" position to allow more air flow. At full throttle, vacuum is much reduced, down to between 1.5 and 3" Hg. At this point the PCV valve is nearly useless, and most combustion gases escape via the "breather tube" where they are then drawn into the engine's intake manifold anyway.

And this on another site.
Check that the engine itself is sealed from outside air. A broken intakemanifold or rocker cover gasket could overtax the PCV system. Seal thePCV system air intake and attach a vacuum gauge to the dipstick opening. Start the engine and let it idle, you should be able to pull 1" to 3" of vacuum on the gauge. Repair any leaks that are found and retest.

So I guess what we are looking for is somewhere near those figures.
Lawrence Slater

No Lawrence, I didn't get to check my HIF today. Other tasks intervened!

You do seem to be progressing with your researches. But I still think that excessive suction level is not the problematic cause with your column of oil scenario, 'though it is with other oil burning problems.

Given the figures that your research is coming up with now, and taking a median figure of 1.5 " Hg. this would lift a column of water about 20", and a column of oil rather more, maybe 25" +. So even a "correct" amount of suction is going to easily draw up your column of oil. It doesn't need a faulty "high" suction level for this to work. Suction level is not the factor determining why some engines appear to behave this way, and some not. Unless of course you take the extreme case of no suction at all (your HIF ?)
Guy W

Yup agreed Guy. You can't suck up oil without any suction, (or very low, - my HIF for some reason), but it doesn't need much suction if the oil is there to be sucked up, as in a timing cover full of the stuff.

So this has really just confirmed to me what I've thought all along, but still not conclusively, why I have a timing cover full of oil at a certain point in warm up/cool down. And as this first happened to me when using the PCV valve system, I probably threw away a perfectly good PCV valve when changing to the Y piece. Given the cost of them now, I wished I'd kept it. :(.

Malc's though could still be different, if he has a faulty PCvalve, allowing too much vacuum to be communicated to the timing cover. Or if the rocker cover breathing arrangement(cap or pipe) isn't allowing the PCvalve to function correctly.
Lawrence Slater

<<Malc's though could still be different>>
Surprising, perhaps, but that is why I keep blathering on about similar symptoms having different causes. It was never an attempt to say that yours wasn't sucking up oil or creating dramatic smoke screens as you seemed to be interpreting my comments. It was simple saying that some others that appear to experience similar symptoms, might well have different causes. ;-)

So, after this little sojurn into the varying vacuum levels being pulled by different systems, we are still left with your original core question. Why, or rather, in what combination of circumstances does oil get sufficiently high in your chaincase to submerge the breather cannister opening? And why doesn't it happen on all engines?
Guy W

LOL. Whilst saying that Malc's "could" be different, my gut says it's not, esp since I started with this problem with a PCV valve. Ha ha. And, there are plenty of others in the archives, on a Y piece and with the same symptom description as mine, Ha ha ha, -- he laughs manically.

"And why doesn't it happen on all engines?" That has to be the billion dollar question. :).

Not far off 200 now. I got the 1st ton on this, who's next?

Lawrence Slater

Actually, given the quantity of oil drawn so quickly into Malc's catch tank I would agree with you. His probably does have the same cause as well as the same symptoms!
Guy W

Almost 200

Lawerance....that is exactly the results I got, when I did the same testing sometime back

Its about 1/2 psi of vacume at the carbs...BUT, differant air filters have a differant effect on the amount of vacume...but still negleageable

On a more sensitive vac gauge... im sure the results areore measurable

But agian... I digress, this is all speculation, theory and alot of guessing....kind of like guessing about the dissy timing is by just listening with our ears or blinking our eyes really fast watching the crank timing mark

We need to know what a vacume / boost gauge on malc engine says to offer any real solutions

Prop and the Blackhole Midget

>>At least it does read something, whereas my HIF on the Sprite registered nothing, and the needle remained on it's stop.<<

I've no idea but if the needle remained on the stop could it also mean that if the stop wasn't there it could show or mean below zero? (blow not suck)
Nigel Atkins

Only on a boost that reads both vac and pressure

On a vac gauge it cant read positive think 0 zero would be the minuime

Prop and the Blackhole Midget

cheers Prop, yes that's what I was wondering, instead of zero vacuum could there be slight pressure (regardless of whether there should or should be)
Nigel Atkins

Prop, is that with or without the kitchen sink plumbed in?
Steven Devine

Found this on ebay while looking for a vac gauge.

It's a Proops Gauge, it has a corelation for vacuum and engine performance.

0 - 5 insHG - accelerate
5 - 10 insHG - high cruise
10 - 16 insHG - low cruise
16 - 20 insHG - idle
20 - 30 insHG - decelerate


Malc Gilliver

I always remember an old engine tuner telling me when I said I wanted the engine running well but with some economy he said the best thing was to fit and drive off a vacuum gauge - that gauge would be what I needed and what he meant
Nigel Atkins

Sorry, childish but 200 !
Malc Gilliver

are the markings on the gauge suitable for all engines (sizes, etc.)?

my navigator would love a gauge like that on the passenger side of my Midget
Nigel Atkins

That is a NICE vac gauge...

If you google how to read a vac gauge, it really is amazing what you can learn from your engine...its without a doulbt the most informitive and diagnostic gauge you can own

It should have been a mandatory gauge in the midget, or for that matter ...any car

The only thing you have to watch is not getting a sensitve vac gauge...something that can measure.avg inches of vac...but yes the above will work and look awsome installed in the dash

Congrats on 200

Prop and the Blackhole Midget

Its a pretty standard vacuum gauge, designed to be connected direct to the inlet manifold. The additional coloured band markings are a fairly rough and ready indication of what happens to the vacuum levels as one opens and closes the carb butterfly on a running engine at different revs. When you open the butterfly fully (accelerate) the carb is on WOT and external air is being easily pulled into the manifold which therefore registers little or no vacuum. Conversely, on over-run the butterfly snaps shut, cutting off the external air supply whilst the fast turning engine is still gulping it in and the manifold vacuum suddenly rockets.

The gauge pretty well just tells you what you already know from your right foot and listening to the engine revs.
Guy W

Nigel.... I just dont think a Vac gauge can hold any positive pressure would be the best its capable of

But im open to being proven wrong....the more I think I know, the less im capable of knowing how badly wrong I really am

Prop and the Blackhole Midget

"""The gauge pretty well just tells you what you already know from your right foot and listening to the engine revs."""

Sorry guy....ive got to disagree

Obviously like all gauges it comes down to inturptation

A vac gauge will easily tell you if you have a blown head gssket by watching the needle flutter at a certian vac needle levels

It can tell you if you got a broken ring, you can even time the dissy ignition with a vac gauge yet never even have to listen just watch the gauge.

Its hard to grasp what is capable... and ive only been a kool aid drinker in recent years

Sorry guy, I still Love you like my brother if that holds any consolation


Prop and the Blackhole Midget

"I still Love you like my brother if that holds any consolation" LOL ! I guess that could be worse!

Idiot gauges, we used to call them. They became popular in this country in 1973 when petrol was in short supply and they even got as far as issuing rationing coupons. They were supposed to help you drive economically aka with your foot off the loud pedal.
Guy W

I wasn't actually meaning to personally contradict you Prop. I was typing my message about how simple and obvious they were whilst you were at the same time busy typing how brilliant they are!

Guy W

Here's one for Lawrence, for when he gets up. ;-)

Tried measuring the vacuum on my HIF. with the engine running, it is pretty constant at different revs. Tick over (900 on the tach) I get about 1.5" Hg. At 4000rpm I can just about get it to nudge the 2" Hg mark.

So getting a definite and reasonably steady reading at 1.5 - 1.8" Hg. More than yours? Or maybe the gauges are just not that accurate at such minimal levels.

Guy W

I'm up now Guy, and missed the 200 mark. lol.

Nigel, if at the point on the HIF I was measuring vacuum, the gauge showed +ve, the engine would either be backfiring, or not running I reckon.

I concur on the indicated vacuum gauges. Some were even simply called REDEX gauges. Guess who marketed them? I had one in my Consul Capri GT, and have to confess, at the time I liked it more for how it looked under the centre of the dash, than for anything it told me. Swinging needles to impress your mates and seduce birds. Most birds though, preferred the swinging of something else. LOL.

I think that's a good reading Guy, and your gauge is probably more accurate than mine. But as I get more from my twins than I do from my HIF, I do think my HIF perhaps has a small problem. I think I may know what at least part of the problem is.

A way back Paul remarked that a stronger spring on the piston could cause a (slightly)higher vacuum at the constant depression area. It's the piston rising that maintains the vacuum at the desired level. But oil plays a part too in regulating the speed of the rise. Recently we all discussed Rylan's cut off HIF dashpot. He was "losing" oil. Well so am I. I've got a cut off dashpot to enable it to fit under the bonnet. I checked it yesterday and it was almost devoid of oil. It still damps, and isn't particularly noticeable when driving. But today I'm going to test it again, with it filled with oil.

Lawrence Slater

And whilst I was on with gauges, I thought I would try and see if I could get any readings off the breather end of the hose. My engine is, I think, fairly well worn at around 70,000 since the last rebuild, and it emits a smoke haze at times. So I would anticipate a moderate level of blow by.

First I tried the gas flow meter off my MIG bottle. It measures flow rate in litres per minute with 1 litre gradations from zero. I thought I might get something but couldn't even get the needle to move off the stop at any revs.

Then penny dropped ! I would need to seal off my oil filler cap. Which I did. Still no reading on the gauge, but this is what I did get ! -)

Guy W

Remind me, is your timing cover into catch tank, open to air? I.e. no suction applied? I can't see any.
Lawrence Slater

Guy's engine just popped in to say Hi !
Malc Gilliver

Timing cover is standard wire-gauze canister which used to feed to a Y piece when I had twin SUs. Then replaced with the HIF. Then added a sealed in-line catch tank with a further gauze but still maintains the PCV sealed suction system.
Guy W

Glove inflated to neatly show the positive crankcase pressure on an otherwise sealed engine ('cos I had blocked the breather pipe with the gauge temporarily fitted.
Guy W

malc. lol.

"('cos I had blocked the breather pipe with the gauge temporarily fitted."

That explains it. Was that at tickover or higher revs? I'll try the same on mine, only with Pink gloves, so we don't confuse people LOL.
Lawrence Slater

And less entertainingly as soon as I simply reconnected the breather hose to my HIF, despite it only pulling about 1.5" Hg vacuum, the glove deflated and is pulled down against the filler cap. Demonstrating that my PCV is working and is sufficient to draw air through the crankcase to keep the nasty fumes at bay. Even with my moderately worn engine.

Lawrence,- photo also shows my Illy can catch tank.

Guy W

The photo was taken at about 2000 rpm, but there was sufficient to maintain the blue erection at tickover too.

Clearly, my litres/min volume gauge was restricting air flow. Given that it is from my MIG gas bottle, it probably records flow rate, but only when accompanied by a high gas-bottle level of pressure.
Guy W

That last test IS the more entertaining. Since it demonstrates very clearly the effect of PCV on the engine. I'll try that on my sprite.

I bet if you also had a timing cover full of oil, you'd have an inlet manifold full of oil too. Or at least a catch tank anyway.

What's in your top hose Guy?
Lawrence Slater

Well, most informative, rather than most entertaining!

One last test, starting the engine with the glove on, but the breather pipe disconnected and simply open to air. At tickover the glove is completely flacid. Any crankcase pressure being generated is being lost to atmosphere via the open breather hose, despite there being no suction applied. This is in effect the situation employed on early pre-PCV systems. They simply evacuated to the air, or at best into a fast air flow across the end of the breather pipe beneath the engine.

Raising the revs, but still with no breather pipe vacuum applied, on my engine blow-by begins to overcome the rate of flow through the breather pipe system (slightly longer and more complex than standard)such that the glove can just about maintain a semi at 3500rpm. A less worn engine would presumably run to higher revs before this happened.

Guy W

I've read that the "scavenge" pipe was ineffective at speeds under 25mph.

I'd say your test shows that at 70K miles, your engine is still pretty good from a blowby perspective.

What's that in your top hose Guy?
Lawrence Slater

Thermostatic switch for the electric fan. Ex scrapyard Fiesta as. AFAIR
Guy W

Ah, good idea that in the top hose.

Well I repeated your experiment with a rubber glove, even the colour, and duplicated the results too. Glove pumped up nicely with sealed breather pipe. When I connected the pipe back to the carb, at mid revs, it almost sucked the glove into the rocker cover, -- seriously. So that gave me an idea.

Albeit that my vacuum gauge reads low, I connected it to the oil filler orifice with some "adapters". I got essentially the same as I got from a direct connection at the HIF breather take off, which on mine was barely 0.5 ins hg, if I repeatedly pumped the throttle, otherwise zero.. So on your more accurate gauge Guy, that could be 1.5 ins.

I tried the same thing at the dip stick hole. But I couldn't get any reading at all, even though I'm dead certain I had a good seal directly into the block, with the tube removed.

Lawrence Slater

Lawrence, that isn't at all surprising. You are just connecting to the HIF via the extended route through the breather hose, chaincase, crankcase and rocker cover. All connected areas so all at the same pressure, give or take a gentle breeze!

My measurement of 1.5 to 1.8" Hg is the suction the the HIF produces. The blue glove test showed that with the breather connected, it fully defeated the build up of crankcase pressure on my car up to around 3500rpm or slightly above. At this engine speed, despite the HIF pulling nearly 1.8" Hg, the amount of blow by was just inflating the glove so it therefore exceeded a crankcase pressure of 1.8" Hg. It is an indirect way of measuring the amount of blow-by, at least in terms of pressure it will sustain, if not volume of gas generated.
Guy W

Yup yup Guy.

And I now have a problem. Given that my engine ventilation performs as yours does, irrespective of the reading on my vacuum gauge, why does it no longer suck oil? It sucked oil on the twin carbs, but doesn't on an HIF.

There is a definite amount of suction there - on the Sprite with an HIF, and even though I got a slightly higher reading on the Midget with twin SUs, I now just can't see that it's enough to make a difference. I have no choice now, I have to refit the twin SUs to the Sprite to see what happens.

I've been examining the twin HS2s to see if there's any way in which the depression at the breather take off pipes could suddenly increase. All I can come up with, is that if one piston failed to rise when the butterflies opened, one carb would feed the engine, and the carb with the stuck piston would communicate manifold vacuum to the Y piece.

But if the suction isn't increasing, why doesn't it suck oil with the HIF? Has my "fault" gone away? -- At least on the engine currently in the Sprite.

Lawrence Slater

Lawrence, although the comparative suction of twin SU, HIF and at the various outlets under different conditions is interesting, amusing even, I still think it is not relevant to your oil sucking problem. If the opening into the breather becomes submerged, oil will be pulled up the couple of vertical inches of the breather pipe by almost (not quite!) zero " Hg. Well 1" Hg will lift oil about 20", so it presumably needs 0.1"Hg for it to pull a solid column of oil up 2" into the carb / manifold.
Guy W

Lawrence and Guy,
I'm in awe..... hats off to you both.
The level of time and experimentation you've been able to give this is simply staggering.

Love the glove shot LOL

Lawrence, even if a HS2 sticks the balance pipe (assuming you have one) would equalise the pressure at the breather points. There might be a slight difference but I wouldn't expect it to be a material one. But you never know! As Prop said, I would be looking at the filters and how restrictive they are.

Malc, just wondering, have you tested to see if your car dumps oil every time until it's well below the fill point on the dip stick?

Best of....

M McAndrew

LOL Mike. I was ignoring the balance pipe because it didn't fit my theory. I was expecting Guy to pick me up on it. And anyway, I know the pistons were free in the pots. I checked them often enough that's for sure.

Agreed Guy, and that was the point I was making, -- badly. My HIF must be making 1"hg, and as you say, it probably wouldn't need that much to suck oil if the timing cover was full. So, why isn't it sucking oil?

Prior to changing to the HIF it sucked oil, and I expected it to carry on, why wouldn't it have done?

If I put the twin SUs back on, and it DOESN'T suck up oil when cold, then something else has changed in my engine.

Lawrence Slater

I don't know Lawrence. Its a mystery!
Guy W

Anyone read Safety Fast this month? Page 48 has a MGB sucking oil......

Now that's clever.... defo no timing case drain back problem on that one...

I hate to think where that's going to take us......

Best of....
M McAndrew

Oh and the fix....

catch tank vented to atmosphere... LOL
M McAndrew

Breather system vented to atmosphere is not an acceptable fix for a 1275 A series. It won't provide the PCV needed by an A series to minimise rear crank scroll oil leakage - not a problem to a B.
Guy W

I wasn't suggesting it as a definitive fix. In fact I'm not even entertaining it as a fix for a B never mind and A series.

I just found it quite amusing...


M McAndrew


Can you do me a solid ...on the twin SU carbs, can you remove the Y piece and hook the timing cover hose to the rear carb cap off the front carb at its Y connection asking yoh to run the evac system off the rear SU carb only and see how it compares to the HIF and the twin SU carb set up

Im just curious what the result will keep mentioning theres a differance between the 2 carb set im not sure what to expect

Prop and the Blackhole Midget

there's been some top shed engineering going on and whilst mention has been made of variables I wonder if they've figured enough, such as components and parts being worn, part worn, not entirely rebuilt correctly, new or existing parts not fully functioning, etc.

and definitely unscientific (statement at least)
>>I was ignoring the balance pipe because it didn't fit my theory.<<
there's a job for you with the alcohol, gambling and sugar lobbyists :)
Nigel Atkins

If a test dosnt fit ones theory,

then obviously the hammer is to small to get the results that are required


Prop and the Blackhole Midget

Guy & Lawrence .. a very interesting session while I was examining the inside of my eyelids! That glove reminds me of the party we had when we lived on a farm in the '70's. One of our guests inflated a rubber glove quite supstantially and cause great mirth as it was batted round the room. I was so far gone that I was thinking how clever my cow-cocky guests were having specialised cow's udders balloons! Next morning I worked it out when I got a rollicking about where all the kitchen sink golves had gone :-)

I've had a thought about HIF44 v twins: In an earlier post I said that as it was the same engine displacement sucking air through in each case they ought to be the same.

Thinking further, the depression in the carburettor throat at the breather point is governed soley by the combined characteristics of the piston and its spring (assuming filters are OK). If the engine were to suck harder or less, the piston would rise or fall in response and the amount of depression would remain the same. It's not called a constant depression carburetter for nothing! (Depression will increase marginally as the pistone gets further up to the top since the spring's contribution will increase slightly as it's compressed, but that will be a similar effect for any SU set-up so can be ignored for the purposes of this comparison.)

So the two set-ups won't necessarily be the same. It will be the combination of piston weight, piston area and spring strenght which determines the depression, and given that all three of these factors differ between the two types of carb anything could happen. Of course the for the carbs to work the overall result needs to be in the same ballpark, but that doesn't equate to being identical in every SU set-up.

A simple example is when springs are changed in a given carb as part of a tuning process. If a heavier spring is fitted, then the piston is held down more against the air pressure in the venturi and the depression would be a bit higher - and vice versa.

Though having thought all this through, it still leaves the question as why the HIF isn't sucking up oil when Guy's measurements show it has enough suction to do so.

So Lawrence, be a devil and put the twins back on, we're all itching to see what happens :-)
Paul Walbran

>>I was ignoring the balance pipe because it didn't fit my theory.<<
there's a job for you with the alcohol, gambling and sugar lobbyists :)

Not to mention a great deal of the road safety lobby as well.
Paul Walbran

1st job tomorrow is strip and clean the fuel bowls and dashpots on the twin carbs. As the Sprite is currently living on the drive, displaced by the Midget in the garage, I need a dry day to fit the twin SUs to the Sprite. Looks like tomorrow is a dry day.

As yet the weather is pretty mild down here, so I may not get a result anyway, even if the engine conditions are still the same on my Sprite. But at least I'll be ready when it does get cold.

Prop, connecting the vent hose to one carb breather port alone, is something I don't remember trying. So if I can make the car suck oil, I'll give it a try.

I've also sent an email to SU Burlen, to see if I can get a figure out of them for the degree of vacuum on the HS and HIF carbs at the constant depression area.

Thanks Paul. Everyone's going to bed tonight, dreaming of inflated cows, sucking on rubber gloves. LOL. I gained all sorts of jobs, by avoiding/ignoring the facts. :).
Lawrence Slater

Carb porn. D'ya like my stub stacks?

Lost to the morning to something else, so started after lunch. I'd forgotten just how much fun it is farting about with twin carbs. But actually, even though they've been sitting in my loft for 13 years, there wasn't any farting about. Back then, I took them off, wrapped them in plastic and left them. Today, I unpacked them, looked in the fuel bowls and cleaned the dashpots. That it.

Then I started the engine for one last test (to be the subject of another thread). Then I took the HIF off, and put the twins on. Turned on the ignition, -- rapid tick tick, followed by slow tick. No choke as it was so warm today(not connected yet anyway), and the engine was still warm from an hour or so earlier. 2nd press on the solenoid and away it went, steady as a metronome. Made me wonder why I took them off in the first place. Oh yeah, I was a perfectionist back then, and kept balancing the carbs at every opportunity, even though they breath nicely through the leaky spindles LOL. But whatever, it stopped sucking oil with the HIF on.

So where am I now?

Far too warm today for it too suck oil. I wasn't expecting it too. Now I'm waiting for a frosty morning. Did a v/quick test on the breather vacuum at the tail of the Y piece -- as I did on the Midget --, needle just lifted off zero ins hg at fast tick over. As I haven't connected the throttle cable yet, I couldn't see the vacuum gauge in the dash, because I was revving it from under the bonnet. Will do that Saturday, as I'm out all day tomorrow.

Sorry Malc. It's your thread, how's your oil sucking experiment going?

Lawrence Slater


Im more impressed with the heater big of a house/factory does that thing heat

Prop and the Blackhole Midget

No worries Lawrence,

I haven't had the chance to mess with the Sprite, I have just broken a 1/2"sq x 36" long breaker bar trying to get a crankshaft pulley bolt off, replaced with 3/4" square x 36" long + scaffold pole for tomorrows attempt
Malc Gilliver

LOL Prop, never even noticed the MASSIVE power station heat exchanger, was too busy looking at the "Porn".

Lawrence, I guess there's not much in the way of a restriction in those filters.... will need to think again about how you can suck oil with that set up.

Looking forward to the cold morning results but we might have a long wait as you are in the tropics ;)
woulda been sorted up here by last weekend....

Best of....
M McAndrew

Yup still warm even tonight. No need for heating yet. And if I do, I always got the Sprite heater box. LOL.

You do know the crank nut's a LH thread. Don't you Malc? ;).
Lawrence Slater

Theres also a lock washer that folds on top of the nut

That nut is almost impossible to break advice, spend the $40 and buy a 1/2 inch electric impact wrench...its very satisfying to here it go wiiir wiiir and the nut is off in under 5 sec. And the uses hou will find for it are almost unlimited

or if the engine is out....load it in a boot or pick up truck and haul it to a shop with an impact wrench...and tip the guy $5

Anyway...good luck breaking that thing free

Prop and the Blackhole Midget

Nah. Just a BFH on the end of the bar always shocks it free. :).
Lawrence Slater

It's not on the Sprite, it's on a Honda - it's supposed to be tightened to 181lb/ft !!! - 4 years ago when the last timing belt was changed.
Malc Gilliver


There you go little feller.... you shoud have gotten a yer self a Kamasaki


Prop and the Blackhole Midget

181? Just to change a timing belt? Remind me not to buy a Honda.
Lawrence Slater

So... where do you find a torque wrench capable of 181 ft pounds

Unrelated...why 181, and not a rounded of 180, at that extreme force, is 1ft pounds really going to make a differance

Are we going to hit 250 postings ?

Prop and the Blackhole Midget

Yes Prop !

For some reason they use a 19mm bolt and tighten it to 181 lb/ft - actually 245Nm but I guess most people prefer old English units.

Since broke a 3/4 to 1/2 adaptor and now have a 19mm 3/4" drive socket on order to go with the 3/4 extension I bought yesterday.

In all fairness thou, the car is 12 years old, has done 180,000 miles and in total owes me a new cat back exhaust, a clutch and a dizzy,plus normal maintenance.

Last time I found a suitable piece of non public road she screamed round to 8000RPM in top, which is about 160MPH, so has retained most of her 215HP, which on a 2.1 litre nat asp engine isn't bad, once fixed I'll be back to playing with Sprites - lol
Malc Gilliver

yes that reminds me of another bit of brilliant boardroom thinking turning away from a Japanese partner to join(!) with a German outfit that tried to force their engines in where they didn't fit and run off with the (MCC) smart idea of boutique marketing of a separated model range and the advantage of a revived purchased name ... that all end well
Nigel Atkins

"the car is 12 years old, has done 180,000 miles" --- "screamed round to 8000RPM in top, which is about 160MPH, so has retained most of her 215HP,"

Remind me to dump the Spridgets and buy a Honda. lol.

I should know this anyway. My brother, a past owner of a Mkii sprite, loves to remind me about his 1980's Nissan bluebird. That too had done very very silly mileage and just wouldn't fall over. It still went like the clappers when he dumped it in a breakers yard. They know how to build engines them blokes.
Lawrence Slater

Anyway just to keep midly on thread. I connected my throttle and choke cables today and went for a drive. Still too warm for oil sucking, but it did make me wonder why I bothered to convert to a single HIF44. Shows you how fussy I used to be. 10 years ago I didn't like the idle much, and with leaky spindles I couldn't be bothered to keep balancing it. Today it seems ok to me.

And actually, I think I might even prefer the twins over the HIF. The engine 'seems' more responsive than with the HIF. But no difference at all when motoring along. Remind me. Why did I swap?
Lawrence Slater

usually the only thing that went seriously wrong on a Japanese car was/is the selling English dealership

and even they couldn't cock-up the servicing

years ago the MGOC Workshop got a new manager that used to work at a Honda dealership and he told me the Honda workshop had little to do other than routine servicing and if there was a rare occasion where it wasn't that all the lads would gather around the car out of interest - the MG workshop was rather different ! a lot busier with more distressed cars and customers
Nigel Atkins

Lawrence, I resisted the change from my twin SUs for years before switching to the HIF. I just liked the look of them. Always found tuning them simple enough and could never understand why people used to say they "went out of tune all the time". What was that about? Mine never did - once set up they just stayed right until I found an excuse to alter something!

The one big change with the HIF though, was the fuel consumption. For overall driving conditions I found about 25% improvement. Other than that, I would agree with you. Twins look good and go well!
Guy W

LOL Guy. "they just stayed right until I found an excuse to alter something!" That probably sums me up 10 years ago then.
Lawrence Slater

They go out of tune only because people have heard that they do. I remember when I bought my first MG back in the 60's people shook their heads and decreed that the twin carbs were always going off tune, and no doubt that's what many new owners get told.

But they don't go out of tune on their own. That is done by the "tuners". When the engine goes off-tune (usually worn points and related ignition timing change but could be other things like a leaking valve or gasket) having heard that twin carbs go out of tune easily people then think "Aha! those #$%^!! twin carburettors are out of tune" and so start fiddling with them to try and fix the problem. Which of course they don't achieve because the problem wasn't with the carbs in the first place. So they then repeat the myth to the next owner, citing such experience as "eveidence".

The reality is just what Guy has found. Once set, that's it. Other than very minor adjustments every decade or so to compensate for wear. I've yet to find otherwise on any of the cars for which I've been the sole fiddler. Check the compressions are even (a simple listen fo a regualr beat as the engine cranks will do), get tappets & ignition to spec, then finally check the carbs - and they remain spot on for years.
Paul Walbran

I dont paul,

I think its better to be safe then sorry...carb adjustment should be the 1st thing tried, you just never know

You have to remember... moutians and hills can have an effect of atmospheric pressure and poor gas can have a negitive effect on carb performance

Sorry paul


Prop and the Blackhole Midget


I'll take your word for it as when I first had my frogeye Sprite on the road I seemed to be setting the twin SUs every few months other bits being OK. I then fitted a Dellorto 40 DHLA and didn't have to play with the carb again. From the age though the carbs were worn and maybe that was the problem. The car did seem to pull better from lower revs with the Dellorto as well so I didn't look back.
David Billington

David - yes, if the carbs are flogged, especially if air is leaking through the spindles, it will be harder and results will always be limited. In particular, the idle speed will be variable, seldom settling at the same idle speed twice in a row and being tetchy about the additional load that depressing the clutch puts onto an idling engine.

Prop - I'm well familiar with mountains and hills (you should see where I live). But believe me, trying the carbs first without checking the others is exactly why twin carbs have such an unjustified bad reputation. It's the golden rule: Don't touch the carbs till yopu know everything else is correct.
Paul Walbran

Sorry paul,

I wasnt being serious, just making a joke that shows the thinking of peoples thought process when they open the bonnet.

I think its the fact that they are duel carbs...sitting side by side that fit nicely into the Palm of your hand.... Mmmm what else do men like to play with in pairs that fit nicely in the palm of hands, hahaha

There maybe a connection .... hahaha

Prop and the Blackhole Midget

hehe, I like it :-)
Paul Walbran

Paul. "Other than very minor adjustments every decade or so to compensate for wear." -- In the spindles mostly. I might look for a spindle kit for mine. I see minispares sell the bushes for £2.80 each. It's been a long while since I had them apart, but seem to remember the housing was worn more than the spindles, == I think I may have replaced the spindles at some time, so that would explain it.

Has anyone had good results with spindle bushes?

All a waste of time though, if mine starts sucking oil again, coz I'll be back to the HIF, unless I find out why.
Lawrence Slater

Just caught up on the ongoing discussion - interesting about the carb vacuum measures - but - it isn't the vacuum that sucks oil - it is the pressure difference that pushes the oil up the pipes - so even with NO vacuum at the top, if there is a higher pressure than ambient in the crankcase oil will travel upwards.

Removing the oil filler cap or providing LARGE vents to atmosphere will reduce the pressure in the crankcase and hence reduce the lifting of oil.

Reducing the vents with restrictors will just increase the pressure difference.

I am not surprised that the carb throat vents produce little vacuum - they are little different from have a vent in the filter backplate.

As a matter of interest - can Lawrence measure the crankcase pressure directly with PCV disconnected? Would probably need a more sensitive guage.

Chris at Octarine Services


"Removing the oil filler cap or providing LARGE vents to atmosphere will reduce the pressure in the crankcase and hence reduce the lifting of oil."

Rather than try and direct you to the post I just copied and pasted.

"From: Malc Gilliver Staffordshire United Kingdom on 31 October 2013 at 15:16:30 (UK time)
Took rocker box cap off and drove the car, no change at all, pretty much no blue smoke until the temperature gauge moved off 90, then at exactly the same place on the road, great clouds, till it burnt it off again.

It does seem to be a large intake of oil either at start or just after then a burn as everything gets into the intake, then it fizzles out again."

But please keep ideas coming !


I do have worn spindles in my 'twins' , maybe after Prop's post I'll call them 'my puppies' - lol
Malc Gilliver

Hi Chris.
As Malc posted, venting the rocker isn't the solution. And opening the breather pipe, has no record of oil overflowing in these quantities either. It needs some level of suction to pull it up. I've been surprised at just how little that is, but it does need suction. Guy tried to measure the crank case pressure using a MIG flow meter, but obviously not sensitive enough. I haven't got anything else either, but it's not the cause anyway.

My Midget engine shows more signs of blowby than my Sprite engine does. That has twin SUs connected to the breather and doesn't suck oil, whereas my Sprite did suck oil -- and may still do when the weather gets cold enough. This has to be more to do with the level of oil in the timing cover, and why it reaches that level before falling when the temp rises. Obviously that is to do with how fast it flows in, and how fast it drains. Pressure in the crankcase would a factor if it prevented the oil draing into the sump through the small drain holes, but if the large hole in the block face is enough to equalise the pressure, then it can't be.

Lawrence Slater

<<Guy tried to measure the crank case pressure using a MIG flow meter>>

No I didn't! A flow meter wouldn't measure crankcase pressure anyway. It's in the name, I was attempting to measure the volume of blow by, not the pressure that it generated ;-) OK, I suspect you were using something of a short hand to describe my attempt. But volume and pressure are quite distinct parameters. The flow meter didn't respond, not because there was no flow, but because it is a MIG gauge designed to operate with a significant pressure to open the valve.

That is why I used the blue glove test. I could then visually see at what engine speed the glove just began to inflate, (the "semi" erection state) overcoming the breather suction by being connected to my HIF. Having previously measured the vacuum pulled by the HIF as 1.8" Hg I could then see that this "equilibrium" was at around 3500rpm on my engine. By deduction therefore, I can say that at 3500rpm the blow-by on my engine is generating a positive crankcase pressure of + 1.8" Hg, matched by the HIF suction at that speed.

I would further theorise that above 3500rpm the blow by exceeds the capacity of the carb to provide PCV. Crankcase pressure would begin to rise and at this point the crank is positively pumping fumes out to the carb. And it will also reverse the flow through the oil filler cap, which will now emit fumes rather than drawing air in. But since both of these orifices are relatively small and will restrict the volume of gas expelled, the crankcase pressure will then undoubtedly rise.

At higher engine speeds it probably doesn't matter that the crankcase pressure rises as the faster spinning crank will make the rear scroll work faster to keep the oil in! It certainly is a system of dynamic variables!
Guy W

Yep, I was being lazy paraphrasing what you did. Which implied that if there was flow, there must be some degree of pressure. But the gauge isn't sensitive enough to show it.

"And it will also reverse the flow through the oil filler cap, which will now emit fumes rather than drawing air in." In which case there should be evidence of oil around the filler cap intake vents. But on my Sprite, even with low suction from the PCV system, as long as it's connected my filler cap and neck has always been completely dry. No sign at all that the flow has reversed in the oil filler cap.

A bit colder tonight. Nipped to the local shop but still no oil suck. One thing I haven't done lately is top up the oil. I know I'm below max and maybe when I top up it'll suck. I can't decide which I'm hoping for. LOL.
Lawrence Slater

I did say I was theorising! But certainly on my engine above 3500rpm, and with the breather still connected to the HIF, there was still an excess of positive crankcase pressure as the blue glove inflated. It was fixed over the filler cap (cap in situ) demonstrating that gas was being displaced OUT through the filler cap vents. Pretty clear evidence then of a reversal of flow. At tickover, the suction from the HIF was sufficient to fully collapse the glove, pulling it down firmly against the filler cap vents as it tried to draw air in.

But, as with yours, the outside of my filler cap is reasonably clean and oil free. But then inside is that gauze filter which perhaps performs the same function as the wire gauze in the cylinder on the front chaincase - viz. it acts to catch and condense oil from the fumes passing through it.
Guy W

You know what's interesting, is that airflow in from the filer cap and down through the block, is via the cam follower borings. This is also how the oil returns to the sump, and there is very little clearance between the cam followers and the block. So presumably if there's too much pressure in the sump, this must slow down the oil return back to the sump from the rockers. But I've never heard of anyone having a flooded rocker cover.

I wonder if cam followers with the small holes in them have any significant effect, and why do some have them and some not? What were the originals? With holes or without?
Lawrence Slater


There are additional drain passages to allow the oil return, not just the cam follower clearances. See top photo here

If you want to measure small pressure drops why not make a water manometer, just requires water and some plastic tubing.
David Billington

Ah yes, thanks David. :). I guess that's why the rocker doesn't flood then LOL.

That's a great idea about the diy manometer. Length of clear tube with two opposing U bends. Lower U bend filled with water. Assume max of 2.5ins-hg pressure = about 1.3psi. If 1psi will lift water 2.3ft, then need +3ft of tube above the U bend. Mark it off in inches and measure. Does that sound right?
Lawrence Slater

1" Hg = 13.6" water, if my memory of O level physics is still working. so your 2.5"Hg maximum will be 34" water.

You only need one U bend. What you are measuring is the difference of water levels in the two upright held ends of the tube. In fact you don't need any extra U bend, just a length of clear plastic tube doubled up on itself will do it, so long as it doesn't kink in the middle of the loop.
Guy W

For what its worth the original followers did not have any drain holes. The lightened competition ones did to improve oil flow between the cam/follower. They are not there to improve oil flow to the sump. My engine has the standards ones and doesn't suck oil (anymore!)
Bob Beaumont

Cheers Bob. I've often wondered about those. I have a mix of both in my spares, and didn't have a clue which were the originals.

Yup Guy, I reckoned the same, and upped it to + 36" just in case it turned out to be more. How can it be done without a 2nd u bend, or at least a 90 degree bend, to connect the feed end of the U bend filled with water to the filler neck? I figured like this.

Lawrence Slater

Because all you need is a length of plastic tubing, part filled with water. No need for extra U bends as it doesn't matter what shape or length it is, if both ends are open to the air the water level will be the same at each end. (as was commonly used to check levels when setting out landscaping, building foundations, pipe lines and canals - now superseded with fancy and expensive electronic or GPS devices) If you apply increased or decreased pressure to one end, then the difference in levels gives the reading.

I have rather lost track of what exactly you are trying to measure!
Guy W

Yup, got that guy, I used to use water levels meself, it never occured to me that it was a measure of pressure though. Doh. If you don't have a bend in it as I put in my pic, how are you going to get the end into the neck of the rocker cover? Am I being thick? lol

Chris wondered about the crank pressure, I guess not seeing that you'd gotten a good idea of it. Then David suggested a diy manometer to get a more accurate measurement. Seems like a good bit of harmless cost free fun :).
Lawrence Slater

Sorry, just a different wording interpretation. If I were making a temporary manometer like that I wouldn't be spending time finding or making separate U bends, which is how I read your original message. A few feet of flexible tube would suffice. But you are right in that it needs to curve down lower than the oil filler cap to prevent the water just draining down into the engine! In fact, given that under certain circumstances there is a considerable sucking in at the oil filler cap (your collapsed blue glove demonstrated how much!) you might want to add a windscreen washer valve in there somewhere. Or maybe use oil rather than water in the tube.

I am sticking with my long held contention that the vacuum (or pressure) isn't that important, so long as it is regulated when needed (i.e. when connecting a breather to the manifold) What is more interesting is the VOLUME produced from blow by.

If you had a theoretically fully hermetically sealed crankcase, then what would the pressure from blow-by be? Well I think the piston blow-by would be like a pump, and the pressure would rise and rise and rise! I guess the driver of this pump is the explosion in the cylinders so presumably it could go pretty high!

We all know that the crankcase isn't like that. It leaks through breather, oil filler cap, dipstick tube and rear crank seal. So the pressure doesn't go on rising. So long as there is sufficient leakage to allow the VOLUME of blow-by gasses to escape then the pressure won't go above atmospheric. Add to leakage a PCV system and the internal pressure should drop below atmospheric.

But the volume of blow-by increases with revs, so at some point (3500rpm in my case) the breather system becomes overwhelmed and pressure does begin to rise above atmospheric (blue glove inflates). At this point you may expect the rear crank scroll seal to start spewing oil. But if it is spinning that fast maybe this goes some way towards mitigating that leakage.

Guy W

Yup, I didn't explain it fully. I wasn't going to make seperate bends Guy, just bending a length of tube, maybe using a wire coat hanger to keep the shape. The blue markers in my sketch, are the water level at rest.

I agree about the blowby too. I'm sure the prime cause is filling/draining of the timing cover. But obviously it needs suction, and excess pressure can only make it worse. In fact rather than measure the presure at the rocker cover, it would be more useful to measure it at the timing cover, with and without the rocker cover vent blocked off. Just to get some idea of maximum pressure.

I'll do it on the Midget 1st, as that's in the dry of the garage.
Lawrence Slater

Well that was interesting.

I had 43 inches of tube above the water level in the u bend. Tube connected to the hose from the timing cover.

1st run on tickover, with the SPRITE(large hole) oil filler cap on, the water lifted about 1 inch. Bringing up the revs lifted it about 4/5 inches, then it leveled off and didn't rise much more.

2nd run on tickover with the MIDGET(small hole) oil filler cap, the water lifted a little over 2 inches. Bringing up the revs lifted it about 8 inches, then it leveled off and didn't rise much more.

3rd run, on tickover with the oil filler cap removed and my hand blocking the hole. It took about 3 seconds to blast the water our of the tube and up to the ceiling, which is 6 feet above the level the water was sitting at in the U bend.

So if you get a blocked oil filler cap, and no other vents, the pressure rises quickly and significantly. How much exactly I don't know, as I only had 43 inches above the u bend. But obviously more than 2.5" hg.
Lawrence Slater

Sounds like fun!
Blasting the water out doesn't surprise me. The volume of the tube, assuming it is something similar to windscreen washer tubing, will be fairly small so the 43" of tube will quickly fill up and blast water out of the end. It is also presenting a much smaller hole than either of your filler caps. I am reading this in terms of volume of crankcase gasses being generated, rather than the pressure as such. The pressure generated will be a function of how rapidly the volume of gas can escape.
Guy W

Guy, the tube is a lot bigger than the hole in the "correct" oil filler cap(the smaller of the two), and bigger than my washer tube.

What I didn't try was to keep my hand on the oil filler neck, after the water had been blown out. My Midget doesn't suck oil, but since my Sprite "does", I'll try blocking the oil filler cap on both when they're warming up. Maybe I'll see oil being blown out. -- Or sucked out with the aid of pressure.

Lawrence Slater

I think that the pressure is potentially very high, - driven by explosion gasses escaping past the rings as blow-by. A bit like pumping up a bicycle tyre, the pressure exerted by the pump at each stroke may be well over 100psi, but the pressure as measured in the tyre takes a while to rise to that level. Only in this case they tyre has a leak, or multiple leaks. If the leaks are small (small holed filler cap or small diameter manometer tube), then the pressure will rise a bit faster, but it will still take a while to inflate the bike tyre.

Blowing the water out of your tube was because of the volume of trapped air that needed to escape. The pressure to do this could be calculated by working out the weight of the column of water lifted and dividing this by the cross sectional area of the tube. I bet its not very much!
Guy W

Yep Guy.


Blow by is present in all engines; its just a matter of degree. So all engines have the potential for crank case pressure. (there is no other way of getting that pressure that I know of).

A 'vacuum' effect on earth is simply a movement of gasses from a relatively 'higher' to a relatively 'lower' pressure area or part of a system.

I'l exit left now.
Dave Squire

Dave - exactly what I was saying - it isn't vacuum that lifts the water/oil - it is the higher pressure at one end that pushes it up! Schoolboy physics!
Chris at Octarine Services

Thing is though Chris, I've definitely got significant blowby on my midget, but it doesn't suck oil. And before I rebuilt the engines on the Sprite, both smoked like chimneys, but didn't suck oil. There's more to this than blowby, but I'm sure it doesn't help.
Lawrence Slater

There are just two factors which result in crankcase pressure. One is the amount of blow-by. And even a small amount of blow by has the potential to produce very high pressures after a few moments (like the bicycle pump analogy)

And the other is how well sealed the crankcase is. If it is open to atmosphere with large unrestricted pathways, the crankcase will not build up any significant pressure as it is, in effect pumping direct to the open atmosphere. But if it is closely sealed then the pressure can rise pretty quickly, even with only moderate blow-by. So maybe the oil being blown out the breather is a function of other "outlets" being effectively sealed on a newly rebuilt engine. This would include a tight rear scroll seal, well fitted dipstick and maybe a restricted breather hole on the oil filler cap.
Guy W


After 287 comments, the solution we came up with is needs new piston rings and a cly hone at the very least and maybe evenba valve job

With the cly compression only being an avg of 115 psi, I guess we found the source of the blow by

Prop and the Blackhole Midget

Sure as hell hope not, drove the car yesterday, started from cold, ran around the block, no burnt oil, but it dumped about another 0.3 litre of oil in to the catch tank.

I'm not rebuilding an engine, if as Lawrence pointed out, it didn't suck oil before, but did afterwards.

There has got to be a simple reason why it siphons a slug of oil out the engine on start up.

Either conditions to raise the column of oil are present at the time the engine stops and it just sits there while the engine cools, so that when I start up and the oil warms up slowly the oil gets sucked in, or the oil always drains back but on a cold start something in the way the engine starts up, or the way I drive cause a column of oil to fill the vacuum system.
Malc Gilliver

I really think this whole diversion into pressure in the crankcase, or suction at the carbs, is an irrelevance to the "oil column" scenario. The pressure needed to lift a column of oil is so slight that any engine with a connection to carb or manifold (via a PCV Valve) would suck up an oil column, - if it was there to be sucked up.

Worn engines, suffering from poor sealing rings and blow-by, emit a continuous blue haze of burnt oil. This is oil vapour from the crankcase being blown (or sucked) out into the induction manifold and burnt in the cylinders. The worse the blow-by, the more oil vapour pours out and the worse the blue haze becomes. Add to this oil not efficiently scraped off the bores so that it remains to be burnt within the combustion chamber.
None of this produces the "column of oil" condition, however badly the engine is worn.

There is another condition where a slug, or glob of oil forms within the breather hose, possibly condensing oil as an engine cools. Later, when the car is restarted, or soon after as the hose warms up, this glob of oily phlegm breaks free and is sucked through and into the intake. Result, a sudden dense cloud of thick blue smoke that lasts fore a few seconds, gradually clearing as the car clears its through a few times. This maybe lasts from 10 to 30 seconds, and is quite dramatic. But it wouldn't produce 1/2 pint of oil in a catch tank!

This oil column problem can surely only occur when the lower end of the breather system is actually submerged in oil. This may be that the chaincase cannister is flooded, or that the chaincase itself is flooded. It will then pull the "column of oil" up into the breather but only until sufficient air (crankcase gasses) becomes available to break the syphon effect. As soon as air is pulled into the breather system (probably at the opening into the cannister)the continuous oil suction will be broken and the system will begin to clear itself, although this would take a while.
Guy W

My experience supports Guy's thoughts. When my oil level was near MIN in the dipstick I had no problems. Nearer MAX and it carried over!
GraemeW (Kent!)

I wonder if a normally running engine might, under certain circumstances, be pulling oil laden vapour through the breather canister as it should. And within the canister (which I believe is a condensing device) the condensed oil isn't running back down into the chaincase as it should so the cannister itself gradually fills with condensed oil. When the level reaches the neck at the top of the cannister and it can no longer draw air through, it will suddenly slurp the whole contents through in one go.

This is how the cannister works, and why I think of it as an oil condensing device:
It has a restricted lower entrance to the interior of the engine, through which it draws engine crankcase gasses, and oil vapour. The hole is matched to the holes in the vented filler cap so it can draw fresh air in and purge the crankcase of nasty corrosive gasses.
The gas enters into the canister where it is much wider so the gas velocity suddenly slows. This drop in velocity causes the gas to drop some of the suspended load (i.e.the oil vapour droplets) which collect on the wire gauze, coalesce and run back down into the chaincase. This condensation process is further helped by having the canister directly in the air flow from the fan, and although this air has been heated by the radiator, the air speed will still help to cool the canister.

This sudden increase in the size of the breather pathway from the entrance orifice, to the canister itself is critical in getting the gas flow rate to drop, and oil to be deposited. If the entrance hole is too large there won't be a corresponding drop in velocity and it will retain too much oil in the vapour drawn out to the carbs. If the hole is too small there is the risk of it getting blocked, or at least impeded by thick oil unable to drain out fast enough when the engine is still cold. . . . .
Guy W

"Worn engines, suffering from poor sealing rings and blow-by, emit a continuous blue haze of burnt oil. This is oil vapour from the crankcase being blown (or sucked) out into the induction manifold and burnt in the cylinders. "

No - most of the haze results from worn engines having worn rings that act act oil pumps* as the piston travels up & down the bores - this leaves oil to be burnt in the combustion chamber - also oil is sucked down worn valve guides and into the combustion chamber.

* As the piston goes down the ring is pressed upwards in the groove leaving a gap under the ring - oil is scraped off the wall and travels between the ring and its groove - this oil is then transferred to the top of the ring as the piston goes up and squeezed out above the ring as it starts to go down on the next stroke leaving the oil on the top of the bore to be burnt.

It is wear on the bottom of the ring that causes leakage - not wear on the face of the ring as commonly thought.
Chris at Octarine Services

"I really think this whole diversion ---- "

I mostly agree Guy, but you can't ingest a column of oil without suction. It is a diversion though, neccessitated by other peoples questions and comments. But leaving suction and pressure aside then, as I've been arguing all along, the timing cover has to be filled with oil at some point for this to happen.

"When the level reaches the neck at the top of the cannister and it can no longer draw air through, it will suddenly slurp the whole contents through in one go."

The canister "alone" can't contain enough oil to back this up. I've already shown this by measuring it, and pouring the oil into a jug. -- see other thread. And Malc proved it too by collecting 1/2 pint in a catch tank. Also if the oil has reached the neck at the top of the canister, it wouldn't be possible to draw any air. Even being half full of oil stops air being drawn through it. The cannister only contains 1 inch of wire mesh, the rest is empty space. Sucking commences before that. It must commence when the internal entrance hole to the breather cannister, is submerged in oil. And that's the mystery. Why does that happen?

Malc. People have fixed this by altering the PCV system, for example by adding additional outlets. I don't want to do that. I want to find why the standard system isn't working. Something I did when I rebuilt my engines started the oil sucking, and the same is true for many posters in the archives. so as you say there has to be a reason. I no longer say simple though. Actually it begins to look far more subtle/complex.

It's not the way you drive, in as much as the car doesn't need to be in motion. I've had it suck up oil on a cold day sitting on the drive. And it happened to graeme sitting in his garage if I remembver his posts correctly.

The timing chain and sprockets need oil. They are fed oil, via the front camshaft bearing and to a lesser extent the front main bearing. The oil has to drain. It does this via two small holes in the front main cap. On almost all Spridgets this works ok, -- no oil suck. Even when the oil is cold and thick, there's no oil suck, so the drain holes must be big enough. Hence in oil sucking engines, either the drains are blocked, or the feed is too great, or it's a combination. I checked my drains, and they were completely clear. That leaves the oil feed. And oddly, this seems to be connected in some way to the oil level in the sump. In addition to graeme, I've found others in the archives who describe the level as being critical. New oil seems to be a factor too, which makes sense since it will drain less well.

I'm trying to make my engine suck oil again. I going to do an oil change -- it's due anyway --and make sure it's filled to just above max. Then all I need is another frost for ideal cold conditions.
Lawrence Slater

Repeating pic and post from the other thread. 1/3rd pint of oil. My hose contains another 1/3rd pint.

"I also filled the timing chain cover with water, - with the chain and sprockets inside. 1/2 a pint or thereabouts. So if it is full of oil when this starts, that's a lot of oil to draw on, and explains it nicely. The question remains, how is it filling/not draining?"

Lawrence Slater

Pic for clarity.

Lawrence Slater

" but you can't ingest a column of oil without suction"

yes you can!! as was proven by you! -

"3rd run, on tickover with the oil filler cap removed and my hand blocking the hole. It took about 3 seconds to blast the water our of the tube and up to the ceiling, which is 6 feet above the level the water was sitting at in the U bend."

There was no suction on the top of your tube - just pressure higher than atmospheric at the bottom end.

So let's just suppose that there is a constant flow of air/oil through the breather system due to the crankcase pressure - this results in oil being deposited in the can and associated tubing - eventually the accumulation of oil is such that a slug of oil travels as far as the induction manifold - a bit like having a runny nose - you sniff the fluid back again and again until - yuk!

What I can't explain is the quantity - except that perhaps it is not just the can - it is the pipework above and below the can plus the volume of the chain case - so the end of the "nose" is actually the vent and drain holes in the front plate.

Perhaps making these bigger or drilling extra vents will allow the "nose" to dribble more than ingest the oil?

This might also explain the oil sump level effect - the bottom holes will be covered in sump oil if the level is high - leaving just the vent hole in the top of the plate for air to flow through ..
Chris at Octarine Services

Pumping and suction are the same thing, just seen from the other end of the tunnel! Both result simply from a difference of pressures, in this case between the pressure inside of the crankcase and the outside world where it is 14.5 lbs/sq ". Or, if connected to a PCV system it may be a pound or two less. If the breather is not attached to a vacuum generating device, and pressure rises inside the crankcase, the outside world provides the suction.But so little suction is needed to draw oil up, that almost any pressure difference between inside and outside will lift oil up the tube.

Chris, you didn't read all that I said! I did also say "Add to this oil not efficiently scraped off the bores so that it remains to be burnt within the combustion chamber." but it is interesting to have your proper explanation about how oil is left by the rings to be burnt.
Guy W

Lot of theories. I see it this way.
Oil flows into timing cover then drains out. How quickly that happens depends on the viscoity and flow rates. It builds up a "head" in the cover which will change as things warm up and so on. The head generates the static pressure which causes the flow out.
This head is relative to the "at rest" oil level.
In my experience if the "at rest" level is low, the oil keeps below the breather.... no issue.
If I top up my oil, everything gets relatively higher, the breather floods and the pcv sucks it up!. Far too much oil carry over to be vapour or the odd "spit"
And it is never pushed out by any crankcase pressures.
But I suspect there are a lot of different causes.
GraemeW (Kent!)

300, lol.

And you didn't read all I've said either Chris. ;).

My oil filler caps aren't, and have never been blocked. Hence if there was a pressure build up due to blowby, the pressure escapes via the oil filler cap vents. See Guy's glove. I copied that and got the same results.

Also, even though I deliberately blocked my rocker cover filleer hole, the only thing blasted out was water. -- not oil. It would only be oil if the timing cover was full of it, and that requires over filling or a failure to drain.

You also say, " -- the bottom holes will be covered in sump oil if the level is high --"

Yes they would, BUT, the sump oil level at maximum is way lower than the drain holes. 5 inches lower in fact. So how is the oil going to rise up that high?

See the pic below, I posted this earlier this year, and discussed it 14 days ago in this thread.

Lawrence Slater

PS. I don't say that the oil level in the sump is irrelevant. I know that in some way it "is" relevant.

I've been wondering if the crank paddles lift the oil high enough to interfere with the drains, but are only able to do this when the sump level is at max, and the oil is cold enough.

However, that can't be the single cause. If it was, then ALL spridget engines would suck oil when their sumps were at max, and they don't. So there still has to be something else going on, that overfills the timing cover in the first place. Then the sump level become the deciding factor perhaps.
Lawrence Slater


We have alot of theory, lets start listing solutions

So lets start with a brief discription of what why its happening and the best possiable solution...I will start

To much blow by positive pressure (115 psi compression) and to much manifold vacume fighting each other

Solution.... new rings, cly hone, valve job, and reroute the canister hose to the carbs using a vented carb spacers

Whos next ?

Prop and the Blackhole Midget

OK -let's tackle this from another angle - why is the can on the timing cover anyway?

The original Sprite & Midget had the breather pipe on the rocker cover linked direct to the inside of the air cleaner where the fumes were ingested by the engine.

Then the 1098 engine had a can on the tappet chest cover - similar to the MGB - attached to positive ventilation valve on the inlet manifold.

Then along came the 1275 engine with no tappet chest covers and some bright spark at BMC stuck the can on the timing cover, where it has been causing trouble ever since!

Solution - go back to the original setup?
Chris at Octarine Services

Does the crank immerse in oil as it spins? I thought not. I have never measured it but assumed the journals and "paddles" spun clear of the oil in the sump. It would be quite a drag on the rotating parts..

Its got to be the relationship between oil being pumped at high pressure into the chaincase via the camshaft, and the rate that it will drain by gravity alone back through the two holes by the front bearing. When oil is hot it will flow away quite readily, but when cold and viscous it perhaps just doesn't get away fast enough. By comparison, the pressurised flow rate in will deliver almost as much when cold as when hot with a good 70psi behind it.

And if this relationship is marginal, it could explain why some engines overfill their chaincases, and some do not. A slightly worn cam shaft bearing and triangular plate allowing more oil in; less wear on other bearings fed by the same oil gallery; fresh thicker oil; high capacity oil pump? different ambient temperatures; different drain hole sizes?; partial misalignment of holes between front plate and bearing cap; different chaincase design (does it have the oil deflector?)crank oil thrower the right way round?; Different levels of oil in the sump; Is that enough variables? There are probably lots more!
Guy W

Chris, my understanding is that the lower capacity and lower performance engines coped with blow-by by having a standard ventilation to atmosphere. As performance (revs) and capacity increased this was no longer sufficient and steps were taken to provide an assisted system, with PCV. This coinciding with less toleration of engines that continually dripped oil from the primitive rear crank scroll seal.

First attempt was the long breather pipe down to below the engine where the end of the pipe is in the air stream, providing some suction at speed. But this wasn't sufficient, particularly at lower speeds. So a PCV system was installed. And the design of the canister on the front of the chaincase was to provide an oil condenser as I explained earlier.

Go back to the original setup? Not for a 1275 or it will pour oil out of the scroll seal!
Guy W

I thought the oil flowed back into the engine crank case by way of that little jagged knockout hole just blow the crank shaft.... the hole that looks like someone at BMC sole job was to strike a hole with a ball pen hammer all day

Does the sister engine have the same issues A+ series....there oil seperator is on the side of the engine, next to #1 cly...that woukd be an interesting experiment...then you just need a A+ timing cover without the canister

I just assumed the crankshaft never made contact inside the sump... because it would cause a huge foaming mess that wouldnt flow into the oil gallies very well, oil/air combo...but thats just my opinion

Prop and the Blackhole Midget

Boy oh boy oh boy oh boy. How can the same things be repeated so many times and not sink in?

1). NOT all 1275 engines suck oil, EVEN THOUGH, they have the SAME PCV set up. -- Be that the valve into the inlet manifold or the Y piece into the carbs. And they didn't do it in the first winters of their existence, or even when they had done 100K miles.

Which leads to --- :

2).Often this happens AFTER an engine has JUST BEEN REBUILT. Or perhaps to an engine that has been PARTIALLY rebuilt.

The timing cover OVER fills with oil , either due to excess supply, or slow drain, or a combination. Suction pulls it into the engine, either via the PCVvalve, or the Y piece.

The "solution" is NOT to rebuild/rebore the engine, or change to a different kind of crankcase ventilation system. But rather to identify the cause, and fix THAT. Of course fitting additional vents in different locations might remove the symptons. But I for one prefer to find out what's going on and rectify that.

Guy, now you're quoting my theory of the cam plate. :). The journals spin clear of the sump oil, but I'm not so sure if the paddles do. I haven't got my sump off to measure the depth of the paddles, but if they don't contact the sump oil, then how else is an "oil mist" created?

Anyone have a side view pic of an a-series with the sump off?

Prop. The oil drains via the two holes in the front main cap. Not sure how it drains on a Triumph 1500 engine, but this is an A series engine we're talking about.

Lawrence Slater

LOL! Its hardly your theory that oil enters via the cam plate! That is what it is designed that way for!

I doubt very much that you are going to ever find a single item that will fix and cure the problem. If you are one of the few unlucky ones to experience this it will be because of an unfortunate combination of a number of elements that come together to cause the front chaincase to overfill. Each taken singly probably has almost no discernible difference. But if a number of them add up, rather than canceling each other out - then you get the problem. Just glad I have never experienced it.
Guy W

Ah, but, it's MY theory the TOO MUCH oil enters via the camplate/front cam bearing. I've been saying so since 1998. :). And in fact way before that in the 1980's, when I rang BMC oxford technical to ask them about it.

I'm not so sure there won't be a "primary" cause. When you look at the archive posts on this there are some common factors. Often engine has been rebuilt, often has high oil pressure, often the level in the sump is mentioned too.

I agree, there are probably a number of contributory factors, but with one more important factor(unknown as yet), without whose presence, the others wouldn't matter.
Lawrence Slater

IIRC PCV's were introduced about 1964 as a pollution control device. The B certainly got it then and I think the Mk2 Midget got it too. The beneficial effects on rear scroll oil leaks were a happy side effect.

Lawrence, while I concur with the overall direction of what you propose as the cause, can you go over (again) how you arrive at this 1/3 pint. The amount worries me - if you dump that much oil into the induction system at once I'd have thought it would kill the engine.

An example: Son Andrew overfilled the K Midget sump by 1/2 litre when he changed to oil immediately prior to an autotest held as part of the local classic concours/car show. The autotest is an elimination series so we do the course several times over the course of the day. Part of the test was you guys call a J-turn (a name which is completely wrong if the manoeuvre is done correctly but I'll use it so you know what I'm talking about). The end result was that with 1/2 litre too much oil in the sump the massive flick of the nose of the car during the J-turn chucked the sump contents forward and completely overpowered no 1 cyl rings. An engine that never burnt any oil suddenly produced a huge dense smoke screen, so bad we had to stop and wait for it to clear 'cos we couldn't see the cones (not to mention the spectators of which there were many). In the process no 1 plug fouled up. We removed plug, cleaned it and the car ran fine. Until the next run at the test. Same result. We did about 8-10 runs through that test that day and it didn't get any better. (Though we worked out how to navigate the smokescreen without demolishing anything (or anyone) and still won.) By event end I had worked out what was causing it. We drained off the 1/2 litre down to the full mark and the problem went away. No smoke at all, as usual.

So the relevance of all this to my question about the 1/3 pint is this: The oil overpowered the cylinder enough to drwon the plug about 8-10 times, and yet the oil level didn't drop significantly. So it doesn't take much oil to drown a plug.

If the 1/3 pint is correct, then all I can work out is it's drip fed (relative to our J-turn dump) over several seconds and not enough to get critcal.

Malc - can you confirm that your 1/3 litre was just from a single start-up. Looks that way from what you say but just wanted to be sure.
Paul Walbran

"Go back to the original setup? Not for a 1275 or it will pour oil out of the scroll seal!"

Here is my 1340cc (1275 block) stage 2 Sprite with a simple large bore rubber hose from can to K&N backplate - the engine has a CR of 10.5 to 1 and produces 97 bhp and not a single drop of oil from the rear scroll seal which was properly attended to during the rebuild.

It doesn't suck/burn oil either - but it DID when intitailly set up with the manifold mounted PCV!
Chris at Octarine Services

Photo -

Chris at Octarine Services

Well Chris, connecting to the K & N backplate will still be providing a PCV system, so that doesn't surprise me.
Guy W

So when are we going to start talking about solutions

We have covered cause and effect to we are just in broken record mode

Solutions people solutions....what are the fixes for All the theorys we have put forth

Prop and the Blackhole Midget

Hi Paul. When this first happened to my engine, I couldn't believe the amount of oil either. Literally dripping from the exhaust tail pipe. Yup you'd think the engine would stall, but it didn't. So the first thing I did was to fit a clear plastic hose to see if it was filling up, and it was. All the way from the cannister outlet to the PCV valve, and later to the Y piece when I converted to it.

My clear hose alone, from the timing cover to the Y piece, can contain 1/3rd of a pint. I calculated it and measured it. The cannister alone can contain 1/3rd pint. Calculated and measured. The timing cover with the chain and sprockets sitting in it -- with the cannister bloked off, contains about 1/2 pint. Measured with water.

For this to happen the timing cover must be filled at least to the top of the internal hole in the timing cover. That's the initial reservior. A little less than it's full 1/2 pint, but more than a 1/3rd. That gets sucked into the cannister and up to the hose. If it stopped there it would be at least 1/3rd of a pint, but it doesn't stop immediately, it continues for at least a minute if you let it.

Malc's first measure in the catch tank was 0.8 of a pint. There's no doubt about the quantity of oil being sucked up, and of course it does cause the sump level to drop. At some point it seems, the sump level drops sufficiently for the sucking to stop. And that's a mystery, because there is no direct connection from the PCV system to the reservoir of oil in the sump. Hence my wondering about the crank paddles lifting the sump oil level in some way.

Prop, the solution is to find the underlying cause, and remove it. :). Trouble is, it's a bit illusive. lol.

Lawrence Slater


The first time I ran the car with catch tank it dumped 0.5 ish litre of oil in the tank, second run it dumped 0.3 ish in the catch tank.

I stick to metric measurements as the tank is a 1 litre tank and has a sight tube on the side, so when the oil fills half the tank I assume that is 0.5 litre.

I was going to run the car again yesterday till I checked the dipstick and found it below the MIN measure and didn't want to add seized engine to the issues list.


I'll try and get a useful piccie of the tank to explain
Malc Gilliver

Malc, I'm guessing it won't happen again if you're below min.

I changed my oil yesterday. 6.5 pints of commer's finest 20/50. My oil pressure is now 90psi on start up at about 2500 rpm.

It was too mild yesterday for any results, and the engine was still warm from the oil drain. So now I need a frosty day to run it from really cold. I'll let you know.

If my engine no longer sucks oil though, even with twin carbs, then something must have changed. Could it be my cord rings bedding in over the 10 years since I swapped to an HIF carb? It seems unlikely, but what else could it be?
Lawrence Slater

Is this the clue?
"My oil pressure is now 90psi on start up at about 2500 rpm."

I thought the relief valve lifted off at 70psi. Mine certainly always did, even when the engine was newly built and with a "high capacity" oil pump fitted.
Guy W

90psi is high. I have had a problem with oil pressure recently and after talking to different specialists eg Swiftune etc, its clear that they regulate the pressure back so its no more than 70psi. Also the piston type relief valve can stick until the engine warms up. Some fit the cooper S ball bearing but there seems to be issues with that approach.
Bob Beaumont

If it was a 1500 I would suggest checking the relief valve by taking apart and checking that no one has put a washer in it to increase the pressure / make up for an old or incorrect spring. (its a John Twist approach to old 1500 and MGB 1800 engines low pressure). Is there anything like that could affect an A series?.

Just a thought.
Dave Squire

100:1 that this high oil pressure won't satisfy Lawrence' quest for a simple answer to his oil suction problem! ;-)
Guy W

Malc, Lawrence, thanks for confirming that. We certainly have a curious one on our hands here!
Paul Walbran

Guy. That's only becuause it's not the primary cause. And for the umpteenth time for the record. My springs are the originals, they are the correct length, the valves aren't stuck in the bores, and there are no packing washers present to raise the blood pressure. lol.

I don't know why my oil pressure is so high, and it seems to be a good candidate, until you consider the following.

1). In the last ten years, I've obviously changed my oil before yesterday. I always have 90psi oil pressure after doing that. And yet NO oil sucking. --- WITH the HIF44 carb.

2). Although high oil psi is often common in reported oil suckings, it's NOT present in all. Remember Shaun from Norfolk? In the good news bad news thread? Note the low oil pressure at the end of his posts.

"Phew, thought it was me going mad. I'm in the same boat, engine rebuilt all setup nicely running twin su's and the big K&N filter, y breather connected from the crankcase to the carbs. I also have a tube running from the rocker box to the back plate of the filter. Get five minutes down the road and a plume of smoke from the exhaust. Accelerating makes it worse. Give it a minute and then no smoke. Always seems to happen when the thermostat on the head opens (theory - only mention it as the temp gauge moves). Once it's happened it wont do it again. If I run the engine first on the driveway and let it get warm it will not do it at all." -------

---- "It's a 1972 1275 with a +60 overbore making it 1330 now, before the work it was a 1310. Head has been modified and the pistons dished to lower the CR after a block skim. Typically runs about 30 psi at idle and 50 psi when cruising. Mated to the std 4 speed box. Only got about 150 miles since the rebuild planning several 60 mile trips once I have confidence in it.
Regards Shaun"
Lawrence Slater

Yup it's a wiered one Paul, but we're getting closer to finding out the cause.

The reason being, that I can now re-enter the discussion in the PRESENT tense, rather than the PAST tense.

Yesterday morning, quite unexpectedly given the warmth of the sun, my engine gave re-birth to at least 1/3rd pint of oil, which was eagerly sucked into the bores. Some of it emerged in the form of a thick cloud of rich blue smoke, and some of it passed through in liquid form to drip from my tail pipe. This caused the traffic following me down the A21, to both blast their horns, and swerve around me, as I lost power and slowed down. I pulled into a layby and cut the engine. I waited 30 sec to 1 min and restarted. I hit the throttle and a BIG cloud of blue smoke errupted from the rear. I switched off again for a minute, and then restarted. I let it idle for a minute, gradually increased revs, and it burned off the remains of the previously ingested oil. What happened was that I allowed the oil time to drain out of the timing cover, FASTER than it was being filled. Then as the engine warmed the oil, the oil being thinner drained faster.

When it was clear I continued on up to London, WITH NO TRACE OF OIL BEING BURNED. This is EXACTLY what used to happen in the past on this engine, and to the spare engine. All I've done is put my twin carbs back on.

However. I usually change my oil in the warm weather -- Just for my own comfort. I changed it this time for an experiment really. So I'm wondering if, NEW oil in the cold weather with the HIF might result in the same thing. Hence I'm going to take a few vacuum measurements with the twin carbs again, and then put the HIF back on. If it still sucks oil with the HIF, that elliminates vacuum. If it DOESN'T suck oil with the HIF, that points to vacuum as being a significant factor, -- but still NOT the prime cause.
Lawrence Slater

Just a comment on Shaun's post, he doesn't say what his oil pressure is on start up. just " Typically runs about 30 PSI when at idle and 50 PSI when cruising. ie is that with the engine warm?
Bob Beaumont

Well there you go Lawrence. I didn't say that I thought that you should accept the high oil pressure as the reason. Only that I knew that you wouldn't! Seems I was right with that comment then! ;-)
Guy W

Bob, Shaun's engine had just been rebuilt. So you might expect the oil pressure to be higher than a well worn one, both at idle and at cruise. Actually Shaun's is possibly under what you might expect, esp if those are "hot" readings. Is it likely that when dead cold, his pressure could have been 90psi and fallen all the way to 50psi? I think it's more likely that it was sub 90psi, and yet still sucked oil.

I've just spent a happy hour scouring the archives for oil pressures. Many people report "high" oil pressures as a worry, but none of those particular posters, report oil sucking. Contrast this to the many who report oil sucking as their main worry. Some also say they have high oil pressure, but some report normal oil pressure.

At first glance though, it seems that the higher the psi, the more oil will flow into the timing cover from the camshaft end plate hole. However, it seems it's not that simple. Is the flow "laminar" or "turbulent"? If purely laminar, then flow rate is proportional to pressure. But if turbulent, then the flow rate is proportional to the square root of the pressure. Or to put that another way, the flow rate does increase, but to double the flow, the pressure must be quadrupled.

So a high oil psi won't neccessarily mean a "far" greater flow of oil into the timing cover. We need to know if it's turbulent or laminar. And for that we not only need to decide if the camshaft endplate feed hole is an orrifice or a tube, but we also need to know the viscosity of the oil at any given time. Physics of flow anyone?

Lawrence Slater

Lawrence, I did comment some while back that the oil flow into the chaincase, whilst under pressure, will be less diminished with thick viscous oil (cold engine). Whilst the same cold, thick, oil draining away from the chaincase purely by gravity will be very impeded. This would provide the difference between flow in and flow out under cold conditions. Once warmed up, the difference in flow rate between pumped (in) and gravity (out) will be much less.

OK, that might still leave the question of why some engines and not others, but this might still be explained by higher oil pressure, additional cam bearing wear, or other factors adding up together, rather than cancelling each other out.
Guy W

I made the comment as an ex'sucker'. Mine has a cold oil pressure of about 80PSI which drops back to 70psi odd after a short while. I think the point may be the oil pressure when cold. Mine didn't suck oil after I changed the pipe and cap so it must have been marginal and that little change was enough. If I had 90 psi cold would it still be a problem?. I can't say. I also changed oil from halfords 20/50 to castrol 20/50 and perhaps the characteristics of the the brands of oil make a bit of difference. I think Guy may have a point and its a number of small factors that add up.
Bob Beaumont

yes but the factors must fit 'the theory' if they don't then they don't count

Guy's odds of - '100:1 that this high oil pressure won't satisfy Lawrence' quest for a simple answer to his oil suction problem!' was totally wrong the odds were more like 730-1 and increasing

Lawrence is happy to going round in ever decreasing circles until he disappears up his own oil pipe rather than admit that he might have had things wrong for many years :)

my theory is that he belligerently stuck with an incorrect type of oil filler cap, possibly made a mistake or had a bit of poor or incorrect work done during his engine rebuild - and yes I'll have some of that too higher oil pressure too

that's my theory, it doesn't matter if it's right as it's MY theory, my believe and you can't argue with my believe :)

either that or the problem is related to the supply of front wheel bearings
Nigel Atkins

Nigel, it's sucking oil again, with the MIDGET oil filler cap. The midget oil filler cap has the supposedly "correct" sized hole in the interior. So that rules that out. --- "rather than admit that he might have had things wrong for many years :)"? If you'd read Bob's engine thread properly, the whole way through, you'd know that I said quite early on in it, that I'd be extremely happy if someone pointed out something truly simple, that I'd been doing wrong for years, and that fixed the problem. Nobody has.

"or had a bit of poor or incorrect work done during his engine rebuild" Yep, I've been saying for 25 years plus, that my front cam bearings have been improperly installed(disputed by almost everybody I think), and that I re-used and old cam end plate and that it was distorted. Did you miss that too?

Bob, yours is still a mystery. I believe but just don't understand how, swapping the oil filler cap and hose, solved the problem. I did that way back and it made no difference to mine. Swapping carbs did, and now I've swapped back again, it's sucking again. Although my oil psi is 90 now, in a few weeks it'll be back to the usual 80psi on cold start, and I can guarantee it will still suck oil.

Here's what I wrote here on this bbs about the oil here in 1998. --- "the oil is filing up the timing cover and not being able to drain away sufficiently quickly enough when cold and less fluid, and hence getting sucked right into the inlet". There's nothing new in this speculation. Most posters with the problem work this out for themselves very quickly because it's bloody obvious. The current section of the debate is now focussing on oil psi. Just as without manifold depression creating suction, without oil pressure to pump oil into the timing chain cover, oil sucking wouldn't happen. But neither are the prime cause.

ALL of the factors have some input, but it's my feeling that they all depend on an "x" factor, that has to be present for oil sucking to commence.

What about sump oil level? I read in the archives dozens of comments from people who blithely state "if you overfill the sump you're bound to have a problem, but none explain why it would lead to oil being drawn into the manifold. Most engines out there are driven around with a full sump and a connected PCV system and don't have a problem. Many also have oil pressure of 80 at start up, and don't have a problem. Some in the archives report 100psi due to a stuck relief valve, but don't report oil sucking.

Guy, I saw your earlier comment about oil viscosity. "-- when cold and viscous it perhaps just doesn't get away fast enough" And that's true for ALL the a series engines. They ALL have exactly the same number and size of drain holes. So unless blocked, it's not a variable factor. The only way the drain rate can be a variable factor is if something other than oil viscosity is slowing down the drain rate. Perhaps that's where the sump level comes in, but how can it be explained, and why doesn't every engine with a full sump cause a problem.

That leaves the fill rate, which is what I've been mostly concentrating on throughout the debate. And what governs the fill rate is the cam end plate and front cam journal/bearing combination, more than the oil pressure. The oil pressure can escape from the rear of the cam journal and up to the head.

When I first posted on this(1998), nobody had heard of oil sucking. Nobody accepted that a solid column of liquid oil was common. Reading the archive postings since then, it's clear that nobody other than some of those that had the problem thought it was any more than, either broken rings, or leaky valve guides, or oil condensation, or a broken PCV valve, etc etc. Now at least no one is seriously doubting the quantities of oil involved. That's progress at least.

I don't believe that all or most 1275 a-series engines are driving around with a near oil filled timing chain cover, just waiting for something to tip the balance between suck or no suck --. Be it either oil pressure, crankcase pressure or PCV suction. I think the drain holes were calculated to be large enough, to cope with the amount of oil that was calculated to be supplied by the camshaft, to lube the chain and sprockets.

I'm on record as saying that my first instinct was( and it still is), too much oil is getting into the timing cover, to be able to drain away fast enough. Now I have a live working oil sucking engine to experiment on, and to strip and compare with another one that sucks. I'm expecting the "prime" cause to be same in both.
Lawrence Slater

I think there may be a case for the front crankshaft bearing journal to be forcing oil out sideways and producing a curtain of oil directly above the drain holes. This could either impede or simply add to the quantity of oil trying to drain - especially under initial higher pressure. In this respect there must surely be a finely balanced relationship between relief blow off pressure,oil viscosity and the speed that oil that can drain out through the front cap - even without adding crankcase pressurisation and suction as additional variables.

F Pollock

To Malc Gilliver.


In your original post you said that the engine had always vented to air 'on the floor' and on your return home after 2, 70mph, 2 hour runs, had lost 2 litres of oil through the dip stick and it had gone all over the engine. Is this how the breather was on the two runs?

You then say you fitted a PCV to try and solve the problem and THEN got the loads of smoke out of the tail pipe. Correct?

Is this how it was? or was your breather rigged to the PCV during the 2, 2 hour, runs?

Just checking that the 300 plus posts are on subject and not drifting off elsewhere as it were ;-0

Dave Squire

Fergus. I too have been RETHINKING the supply of oil into the timing cover.

Unlike with the BMC MGB workshop manual, there is no official description of how oil is delivered to the A series timing chain and sprockets -- as far as I'm aware. What there is though, are intelligent descriptions of how it happens, based on owners, tuners, and mechanics experience; No doubt making comparisons with the MGB description of how the timing chain tensioner is lubricated. IF WE COMPLETELY IGNORE THE MGB SYSTEM, what do we have?

The main oil gallery feeds oil at high pressure to the crankshaft bearings. From there at REDUCED pressure, oil is fed to the middle and front camshaft bearings. From the front camshaft bearing, pressure is further reduced as the oil is fed to the rockers, and as it leaks out of the front and rear of the camshaft bearing/journal.

And finally, the BIG BONE OF CONTENTION, oil is fed once per revolution, through a hole in the cam end plate, facilitated by a groove in the camshaft journal. NOTE though: This is at reduced pressure, and it's only once per revolution.

Contrast this with what the front crankshaft main bearing is doing. Oil is leaking out of the front at high pressure, and it's constant. JUST LIKE THE REAR crankshaft bearing. The rear crankshaft bearing cap works in conjunction with a scroll on the crank, to return the oil to the sump, and it also needs PCV to prevent it leaking. Suction attempts to cause a slight NEGATIVE depression in the sump, thereby assisting the scroll. The source of that suction, as far as the crankcase is concerned, is the timing chain chamber.

The FRONT main bearing cap is pretty much the same shape as the rear. The big difference is that it has two drain holes drilled in it. The front of the crankshaft doesn't have a scroll. Instead there is an "OIL THROWER", and an oil seal on the timing cover. The negative pressure in the sump is not there to prevent the front crankshaft bearing leaking oil into the timing chain cover. It doesn't need to. The drain holes return it. So what is the oil thrower for? The chain needs lubricating. Oil from the front crank bearing probably supplies sufficient oil, and the thrower makes sure it doesn't pool in the bottom of the timing cover.

So back to the camshaft end plate and the hole drilled in it. It has two related functions. It's a thrust washer, designed to keep the camshaft in place, against the forward thrust from the distributor shaft. And it controls the necessary endfloat to keep the sprockets aligned. The white metal side of the cam end plate is the main bearing surface, and it needs constant lubrication. It gets it directly from the oil leaking from the front of the camshaft bearing. The other side of the cam end plate doesn't spend a lot of time in contact with the chain sprocket, but it still needs a bit of oil for when it does make contact. It gets it from the small pulsed oil feed. This oil isn't meant to fill or partially fill the timing cover to lube the chain. That's already taken care of by the crankshaft and oil thrower. But perhaps it is a supplemental oil supply to the chain and sprockets, as it gets thrown around by the cam sprocket.

Hence, just as I've thought all along, but for slightly different reasons, too much oil leaking from the camplate is the prime cause of oil sucking. The evidence lies in pictures, and in remarks by others, who all remarked on the oil thrower. The pictures were supplied by me, and Guy. Guy's picture in particular shows a dry oil congealed front engine plate. It had obviously not been bathed in a constant supply of liquid oil. I also have a pic from another 1275 engine plate that shows the same thing. Contrast this with my spare my engine -- that sucks oil. When I took the timing cover off, the engine plate was clean, and obviously washed in oil.

The cause is as I've thought it to be. Too much oil from the cam endplate, which overwhelms the drain holes. The only way I can be sure is to strip my current engine and see if I find the same as in my spare engine.

How exactly this explains others though, I can't say. We need a mass strip. lol
Lawrence Slater


The engine blew oil out on the motorway runs, but did not burn oil.

I then fitted the PCV system, to cure the oil being blown out and only after fitting the PCV did the car burn oil.



Still haven't photo'd the catch tank as I am using the bonnet of the Sprite to store the cams and followers, timing bets and pulleys from my Honda.

Malc Gilliver


I am not an A series bloke (apart from the few I used in the 70,s) but this is definitely oil being blown out / pushed out / finding its way out and for all I know a gremlin or leprachorn bailing it out through the dip stick aperture.

The newly installed extractor system is stopping this happening and burning the oil instead. It may be that it is going via the timing chain to the newly installed extractor system to be burnt now but it wasn't on the day that Malc discovered the problem. It was coming (being pushed) out of the dip stick rather than the breather presumably because its the lowest point where it can escape and it was too circuitous or the long breather to the floor pipe was blocked or kinked.

IMO this is where its at and we should be finding an answer to fit this.

Dave Squire

<<Guy's picture in particular shows a dry oil congealed front engine plate. It had obviously not been bathed in a constant supply of liquid oil>>
Don't put too much score in this Lawrence. That engine is a 948 for my Frog, last taxed for the road in 1984! So the fact there is any liquid oil on the front cam bearing is quite surprising! ;-)

Second point, I am not sure if you are meaning to imply that the cam plate hole -"the small pulsed oil feed" -is there to just feed oil to the back surface contact with the sprocket. Looking at the wear ring on the front of the cam plate in this photo one can clearly see that the small hole is almost completely outside of the contact surface, delivering oil direct out to the chaincase. See photo.

Also, I thought that the point was that on some engines at least, oil was leaking from the front cam bearing, not just through the designed hole, but also from between the cam plate and the engine front plate, when the cam plate was distorted or worn

And, when you say that the oil feed to the camshaft is at reduced pressure I guess you mean because some of the pressure at the pump is lost by oil escaping at the crankshaft bearings. That makes sense, and I can see that there will be, or at least should be, a drop in pressure. The should be is because when the oil is still cold much less will be escaping at the crank bearings than when hot,so the cam bearing will be getting a pressure feed not very much reduced from the full pump output pressure. Reduced, by not by a lot, and at the cold running condition that the oil column scenario takes place.

Refinements to your comments, not contradictions!

Guy W

Here's another photo, to compare with that last one. This time with the camplate removed. You can see the notch of the oil feed in the cam bearing, top right. And the end of the corresponding groove in the camshaft, having just turned past the point at which it collects its pulse of oil from the cam bearing. It will then continue around clockwise another 240 degrees or so until it registers with the hole in the front plate, ejecting the oil. At least that is how I assume it works.

This engine is a factory reconditioned one, supplied in 1979 so probably not previously dismantled as the car came off the road just 5 years later in 1984.

So the cam end plate is fitted such that the delivery hole is 240 degrees around from the cam bearing. But are the bolt holes equally spaced? looking at it it looks like it could be rotated around such that the plate hole would then align directly with the cam bearing oil supply hole? That would result in much more oil being delivered directly into the chaincase. I thought the bolt holes were not equally spaced in order to avoid this, but in that photo of mine it looks like they are! Thoughts?

Guy W


Sorry to do this to you....

But I agree with you.... (oh thats bad for

I just cant get over the fact that oil is shooting out of ever available weak seal and coating the engine bay via the dip stick holder

Plus ...ALOT of ring wear aka 115 psi avg

Plus the evac system hooked up to the intake manifold that pulls a god awful amount suction

Im sorry, the engine is needs a rebuild... once this engine drops to 105 psi, its game over I cant belive it will still be able to run to any kind drivability

If the huge amount of blow by isnt solved 1st... then everything else is just bar stool engineering

Prop and the Blackhole Midget

Prop, Dave.
Whilst I agree that oil being blown out of the dip stick hole is undesireable, I think you are making too much of the blowby, and the "low" compressioin readings. For one thing, it may be an LC marina engine. Anyway though, it's pretty much accepted that 1300 A series engines need some form of PCV, otherwise even new builds have too much crankcase pressure. Malc's original setup that blew oil from the dipstick, had a sealed oil filler cap and a restricted rocker cover pipe(possibly blocked off?). His timing cover hose may well have been obstructed too. See Guy's glove for the visual effect of that. A 2 hour drive at 70mph with a partially sealed system, will definitely blow oil from somewhere, and the dip stick is a likely place.

My Midget which has the Y piece PCV system, also blows some oil from the dipstick, but it DOESN'T suck oil. I know this because I first drove it on a cold November day last year, and drove it home from London on another cold November day this time last year.

Here's a pic of the Midget oil pressure --- 80+ psi --- at 4000 rpm, a few minutes after starting it from dead cold. It surprised me so I didn't have my camera ready to capture it nudging 90psi.

Lawrence Slater

There is also no guarantee of the accuracy of Spridget gauges! It may, or may not be a true 80 psi.
Guy W

True Guy, in which case my Sprite might be reading too high as well. -- Or too low of course.

To answer your questions Guy.
Re the oil feed into the timing cover to lube the chain and sprockets. I was re-thinking the oil supply, and wonder if the crank actually plays more of a part than it appears too. The oil thrower must be there for a reason. If the oil sits above the level of the crank nose, then the chain itself would throw/drag the oil around, it wouldn't need an extra thrower. And as such the camplate should release very little oil.

So yup, I do still think the camplate and or bearing, could be the major cause, due to leakage.

I don't think many saw/read the last of the "engine breather" thread where I posted some experimental results. So here's a repeat link to a short vid I made last year showing oil emerging from the cam endplate hole. It's self explanatory, other than that, this was the cam plate AFTER I made sure it was in contact with the engine plate ALL the way around. Prior to that it was leaking from the sides.

Here's a pic simulating the camplate leaking from one side.

As regards the rotation of the camplate towards the notch in the bearing, I'll go and check.

Lawrence Slater

My 1330 high compression engine has 100psi at start up which drops to about 80psi after that. I don't lose any oil anywhere!
frogeye Gary

Thanks Gary. Do you have a PCV system connected?

I don't know why the link to the vis isn't working when you click on it, but if you cut and paste it to the browser, it does.
Lawrence Slater

Guy. I checked on the cam plate. It CAN'T be rotated to fit in any other way, than with the oil feed hole adjacent to the larege hole in the block. If you remember it can be fitted reversed -- JUST -- if the holes are distorted a little as mine are. But the oil feed hole is still on the same side as the large block face hole.

So you think that notch in the bearing is a feed hole? I've wondered if it's used with the tool that presses the bearings into place. But you maybe right. And if you are right, then that lends more support to my thinking that MY front camshaft bearings at least, are too far back in the block face. Looking at your picture, and the wiped clean one you posted in "engine breather" Feb 2012, your front cam bearing appears to be flush with the block face, and the cam groove is covered by bearind surface until reaches the notch. On mine though, the front portion of the groove protrudes from the bearing, and is thus always "leaking" oil to the rear of the camplate.

Try this link to my video of oil emerging from the cam plate hole.

PS. There are sounds too. As if I'm on an airfield lol.
Lawrence Slater

No PCV system connected and just the single Hif44
frogeye Gary

Thanks Gary. If oil pressure is causing this, or at least contributing to it, with PCV you might otherwise be sucking oil like a madman. Well your frog would anyway. But no PCV, means no suction on the timing cover. I assume that you have filtered breathers then?

For the last 3 days, about a mile or so AFTER my temp reads 160(stat opens) my Sprite engine begins to suck oil. Today when it began, the oil pressure was at about 80psi. So now I have a consistently oil sucking engine I can try various things on it.

I'm going to try and eliminate the oil pressure as a cause tomorrow. I'll pull the pressure relief spring and valve, and see if amongst my assortment of spares I've got a similar sized but weaker spring. I'll also check to see, -- again, --- if the valve is sticking in the bore. If it's not sticking, then the only thing I can assume is that the oil relief drillings are blocked. Maybe I can get a pipe cleaner down them to check this.
Lawrence Slater

I wasn't sure about whether the cam plate would move around. I seemed to recall that it didn't, but then when I looked at my own photo of that cam plate it looked as if the bolt holes were equidistant. And although that engine isn't fitted in a car at the moment, I didn't really want to go and dismantle it to check. Especially as I knew that someone would be able to confirm or otherwise, what I was saying.

Again, I assumed the notch was something to do with the oil input feed. But on consideration it clearly isn't! It may be something to do with relieving the compression exerted on the cam bearing as it is fitted into place, to prevent distortion at the edge of the bearing. The oil feed hole is further back in the bearing as can clearly be seen in the second of the two photos that Mike (MGMike) posted back on 4th November
Guy W

Assuming lawerance and guy are correct ....

Its a leaking crankshaft / camshaft bearings

This debate is worthless to malec

The fix issue is still going to require a complete engine rebuild where the block mains and the journals will have to be built up with a tig welder then re-machined and then completely re line bored for both the crankshaft and (or) the camshaft

So we are talking some serious cash...$2000 easily for machine work

I think malec has only 2 options...

1. a replacment good used engine

2. Convert to a single hiff 44 carb and intake

Im not sure how a single hiff 44 carb and intake cures a bearing /journal issue, but lawerance is proof that it does

So thats probably the most easiest and economical cure to this guessing $400 - give or take a few beers for a hiff 44 carb and intake manifold

Bottom line its probably a massive and expensive engine rebuild if the HIff 44 dosnt work

No one else has mentioned any solutions to these "Prop like problems"

Prop and the Blackhole Midget

"the block mains and the journals will have to be built up with a tig welder then re-machined and then completely re line bored for both the crankshaft and (or) the camshaft"


Prop, you've really pushed the boat out now LOL :)
Lawrence Slater


I dont know lawerance... how else do you fix that bearing/journal area if its shooting oil out and overfilling the timing chain cover....obviously if its shooting oil out of those areas ....its ither a defect thats gone bad, or wear that is only going to get worse, not better with time

Im pretty sure JB weld and bozoka bubble gum wont fix that type of high pressure oil leak

Prop and the Blackhole Midget

Wow, I cant imagine chasing this as far as it has gone, though it does seem worth knowing. Ive never seen anyone pursuing less oil pressure but it does sound like a good idea in this case to try and eliminate the oil burning problem. Is there any type of filter material that would let air pass but hold the oil back in the pcv tube?

Would an Item like this solve the timing chain issue?

Steven Devine

Hi Laurence,

The only filtered breather that I have on the car is the single air filter on the carb. My rocker cover is unvented.
frogeye Gary

Hi Gary. So how do you vent your crankcase Gary if the rocker box is sealed?

Steven. Yup, sealing the timing cover and venting elsewhere will work. But the aim here is to make the standard system work, -- as it does on most engines which don't get the problem of oil sucking.
Lawrence Slater

If Gary has no discernible venting then that means that his engine is not causing excess pressure otherwise the oil would be blowing out of ...... now let me see .. the dip stick hole? or similar like Malcs was? before the PCV was fitted? So lets see:

On Malcs there would be no clouds of smoke if the PCV had not been fitted after his return home, however there would still be lots of oil leaking, which if the breather was vented through a can to air would collect in the can. (Assuming the vent pipe is not blocked of course in which case it would come out of some other orifice.) So if he now connects the breather to the can and keeps the can venting to air (not through the PCV) and runs the engine and oil collects in the can it is a simple enough test and indication of high crank case pressure or oil being blown out somehow. Under these conditions if oil does not collect in the can then it is not being blown out. (And something has changed since Malc's return home).

The 'sucking up' question will then be answered once and for all and I will go away and let you A series blokes fix it.

As far as I can see this is an independent test of all other variable conditions and gauges and allows clear thinking on the problem.

KISS I believe someone said.
Dave Squire

You know what Laurence, I can't actually think at the moment. When I had the twin carbs it used to vent from the crank case cover (gauze filled canister) to a Y piece then into the carbs, the usual way? Now I think that it's the same set-up but obviously no Y piece and strait into the single carb.
frogeye Gary

Ah I misunderstood you Gary. Do you have an HIF by chance? That has a connection for the hose from the timing cover. If not maybe yours is straight into the back plate of the air filter.?

I tried to reduce my oil pressure today. The two outside pictures shows my spare engine, and the centre picture is the running engine in my Sprite. The pictures shows both springs and pistons inserted as far as they go, without compressing the spring. 24.5mm of spring sticking out on both. The holes don't show any obstructions.

The pistons came out easily on both, but there was some sign of mild scuffing. No signs that either are sticking. Both springs are 71.2 mm according to my vernier caliper.

I was able to poke a pipe cleaner into the relief holes on each, but not far enough to tell if they are clear all the way to the sump. However, as I did on the spare engine (the left most), I put the screwed cap on alone on my running engine, and span it over. Normally I can raise oil pressure easily without starting the engine. But thiis time, no oil pressure at all without the spring and piston. So I'm guessing the relief holes are clear.

Started the engine again, and got 90+ PSI oil pressure. So I don't have a clue how that's happening.

Lawrence Slater

According to the guy at Swifttune they reduce the tension on the spring either by grinding off coils on the spring or by packing out the cap to arrive at 70 psi hot. I see minisport do an adjustable relief valve which has a threaded bolt in the cap to adjust the tension of the spring.
Bob Beaumont

But this is kinda curious though Bob. Standard springs/pistons, no mod's no blockages, and high pressure over the relief figure. Must be a reason for it.
Lawrence Slater

I think I would start by swapping your gauges over. Just as a check.
Guy W

My 1275 has 80 psi (indicated) on start up, 70 when running @ say 3000 hot.
Runs a HIF6 with plastic vented rocker cap and hose into HIF - no oil smoke, its only done about 4000 miles though.

Have had this sort of pressure on my previous cars.
In the day when the 1275 cars were new/nearly new I assisted with the odd deliveries for a main BMC/Leyland dealer and this was what I remember as the norm on good engines.


richard boobier

Not likely to help but I have around 60psi when cold dropping to 30/40 when warm/hot, this I consider to be a gauge "issue"

When I cold start I get one "puff" of blue smoke that dissipates at once never (yet) to return when on the road

There is no corresponding blue smoke when restarting when warm

I use the standard Midget black plastic cap on my aluminium Metro type rocker cover, this seems to allow venting OK

This engine has a HIF with the canister pipe fed into the carb body input spigot and as I took the engine apart in September in a bid to alleviate oil leakage

I wondered if I should fit a catch tank between canister and carb, but as of the present the engine seems to be staying clean and dry

Not something I can attribute to me still noisy type 9


It leaks a little and will be needing some of Nigel's recommended magic oil to quieten it

Comma isn't doing it this time Nigel

Guy. The Midget gauge nudges 90 when dead cold. The Sprite gauge nudges 95+ when dead cold, and the spare gauge (different type) I connected to my spare engine when experimenting, nudged 75psi just running off an electric drill about 1000rpm. Probably less as it began to overheat, so I slowed it down. I can hand crank it with my socket set to 50psi. And to top all that, my Sprite gauge has been changed for a reconditioned one at least twice in the last 20/25 years or so, due to my breaking the temperature sensor capillary tube. It's always had high oil pressure. I'm fairly confident it's not the gauges.

Bill1. You don't need a catch tank. When I had my HIF fitted, the engine didn't suck oil. It's only sucking oil again with the twin SUs back in place. The has to be more, -- even though it's a small amount -- suction.

However I'm going to confirm that. Now that I've got mine sucking oil again, with new oil in cold weather, I'm going to refit the HIF and see what happens. Actually I'm really hoping it "won't" suck oil, because having to stop and let it settle, and constantly looking in the rear view mirror, is a pain in the ar*e. LOL.

Hi Richard. Thanks for confirming that about the oil pressures when new. Sure 90/100 is high. But if you drove new Spridgets with circa 80psi on startup, that seems to indicate we have a misunderstanding about the readings, as related to the pressure relief valve. I've remarked several times that maybe the gauge reads pump pressure and NOT main gallery pressure. It also suggests/backups, that high oil pressure isn't the cause of oil sucking

I'm going to strip the rest of my spare engine soon, and pull the sump off. Then I can take a look at all the gallerries and oil feeds to check for blockages.
Lawrence Slater

I started off thinking that high oil pressure might mean that it delivered oil to the front cam bearing faster. But then on consideration it could equally indicate virtually the opposite of that! Why does one get an oil pressure reading? -Well it is because the rate at which the pumped oil is escaping is being restricted, so the pressure in the galleries rises. So making simple assumptions relating oil flow at the front cam bearing to pressure on a gauge doesn't really stack up.

What is needed is a measure of flow rate, not pressure. Its back to your original issue about the chainacase overfilling. Either it fills too fast or it drains too slow (or both!). It would be good if you could devise a means of measuring these flow rates independently.

Guy W

LOL. Guy it sounds like your mind is doing the same somersaults as mine is over this subject. In the engine breather thread I agreed that high oil pressure could have been the cause. But then other evidence keeps coming out to contradict that.

I agree, a down the line restriction or blockage would force the pressure up at the gauge. I wondered about a blocked filter or filter head. But then my ends are ok and the rockers aren't starved. Of course the filter has it's own bypass means too, but I'd expect over time the engine would be damaged. Plus also, the front cam bearing/timing chain cover is at the end of the oil feed line, and yet there is sufficient oil to put 0.5litres of it into Malcs catch tank.

"It would be good if you could devise a means of measuring these flow rates independently."

I guess the drain rate is easy enough, as Malc said earlier. Just pour oil down the breather canister and see how fast it drains out into the sump. I'll try that when my sump is off. The fill rate though is pretty hard to work out, as you need the engine running and the timing cover on. A clear cover will help, but with all the splashing it may be impossible to see when it's full, and how long it took.
Lawrence Slater

Chaincase cover with an overflow hole to the outside, plus some silicone bath sealer to block the two bottom holes. Then start and run until it begins to overflow, stopwatch in hand.

But what would you learn that you don't already know?

My suspicion is that the rate that oil is pumped in under pressure, varies less with viscosity(i.e. temperature), than does the gravity flow going out. You could test this if you could do measurements with cold and warmed up oil.

So if flow in were just a little bit higher on some engines under normal (warmed up) running conditions, then this wouldn't matter. But the same engine when cold, might overfill the chaincase quite rapidly. So a marginal variation on some engines could therefore make a very significant difference to the behaviour when cold.

Adding my "health warning" (again) others experiencing blue smoke clouds should not be distracted by this ongoing discussion, into assuming theirs is necessarily the same issue as the sucking of a column of oil. It may be, but there can still be other reasons!
Guy W

Good idea with the fill test. I agree, it will only confirm what we already think is happening. But nice to have it confirmed though.

I hear what you say about viscosity and draining Guy, but there are TWO definite factors that we KNOW affect oil sucking. Temperature is one of them, and the level of oil in the sump is the other. Pretty much every poster has recorded both of these as being a factor. But HOW are they linked?

Most frequently this happens on cold days, and always when the engine is cold. When the engine is hot the problem doesn't show up.

My engine stat opens at 160. I drained my oil the other day, after my stat opened. I was surprised at how " cool" the oil still was, and how slow it was draining, even though my engine had been running for 5 min's after the stat opened. So I stopped draining it, and got it much hotter to make it drain properly. This made me think more about what's happening when my engine sucks oil.

1. The engine starts, and COLD oil is fed into to the timing cover.

2. The radiator fan is blasting COLD air onto the timing cover, keeping the already cold oil, - "cold", and slowing drainage.

3. Gradually the engine heats up, and warms the oil in the block and sump with it. The oil thins and flows more easily INTO the timing cover. BUT, the fan cools the oil in the timing cover, and thus keeps the drain rate lower than it needs to be. Not enough "cold" oil is draining back into the sump at this stage.

4. The timing cover fills too far and oil is sucked up. THIS EMPTIES THE TIMING COVER. Thus removing a lot of the "cold" oil, or maybe all of it from the timing cover.

4. Meanwhile "warmer" oil is fed into the timing cover, which drains into the sump more quickly. Gradually, all the oil is warm enough, thin enough, and drains quickly enough as it is fed into the timing cover.

5. This brings us to how the SUMP OIL LEVEL might affect this.
The more oil there is in the sump, the longer it takes for the oil to warm through, and thin sufficiently to be able to drain fast enough from the timing cover. As the sump level drops, the oil will circulate more quickly, and hence get hotter and thinner faster.

Why doesn't this happen to ALL engines then?
There must be some shared "defect" in the affected engines. The timing cover drain rate is fixed by the size of the drain holes. So there must be some factor that increases the fill rate. Perhaps there is also something other than cold oil that slows the drain rate. But if the holes are clear, what is it?

I wonder if placing an insulating cover over the timing cover, might change the temp just enough to allow the oil to stay warm enough to drain more quickly?
Lawrence Slater

Malc. What type of fan do you have? Do you have the original, or the later multi blade plastic fan? We both have the vertical flow radiator. I changed from the original metal blade fan, to the multi blade plastic one many yonks ago.

Originally the vertcal rad was coupled the simple two blade fan. Could the multi blade fan, combined with the vertical radiator shroud, be keeping the temperature of the timing cover and breather canister too cold? Particularly when the engine is first warming up?

Lawrence Slater

I agree that oil temerature is critical but I have the later multi bladed plastic fan on the engine in the frog and don't now experience oil sucking.
Bob Beaumont

Now you've spoiled my theory again Bob. LOL. Maybe you're the exception that proves the rule.;). Out of interest though, do you have a vertical or cross flow rad?

My stat opens at 160, and the oil sucking commences after that. The stat opens and cools the block, and hence the oil. Maybe if I fit a hotter stat, it might keep the oil warming long enough to thin before it sucks up? Worth a try anyway.

Lawrence Slater

Sorry Lawrence! its a standard vertical flow. On the thermostat theory, I have always run the engine without a thermostat but with the normal blanking sleeve.Its also got an oil cooler without a stat in it as well. So whilst I agree its a temperature issue it may not be that critical as mine must take longer to warm up (don't I know it in the winter!)
Bob Beaumont

re your theory point 5 - I doubt very much if the additional 1/2" or so of oil is enough of a percentage of the total sump capacity to make sufficient difference to the temperature. But it may make a difference to how FAST the pump lifts the oil as it has less height to pull the oil to prime the pump. With cold oil, it will begin to flow through the system sooner with a fuller sump.

you say "I hear what you say about viscosity and draining". but I think you misunderstand me as the point I was making wasn't about draining, it was about the rate of FILLING. The point is that because it is a forced feed, the rate of flow IN is less reduced by low temperatures, compared to pumping hot, thinned oil. The flow out is not a forced flow; -well only by gravity.
Guy W

Cheers Bob. If I hadn't read your original descriptions, I would say that yours was a different type of oil sucking. Changing the hose and cap on mine has no effect.

"I doubt very much if the additional 1/2" or so of oil is enough ---- ". "But it may make a difference to how FAST the pump lifts the oil as it has less height to pull the oil to prime the pump".

Surely though Guy, the oil feed pipe is ALWAYS below the surface of the level of oil in the sump. So the oil is always pulled up the same height. Otherwise there would be multiple occasions that the pump would run dry.

" -- the rate of flow IN is less reduced by low temperatures --" Maybe so, but how much less reduced? It maybe, that initially the fill rate is matched by the drain rate. Then as the engine, and hence the oil begins to warm and thin, there is a sufficient "pumped" oil feed, to outstrip the gravity fed drains, until the oil is thin enough to drain more freely. If it's that marginal, then anything that keeps the oil cool in the timing cover will exacerbate the problem.

They're just ideas and it's all "guesswork" anyway. The hard facts are that it happens. It happens as the engine (oil) reaches a certain temperature, be that warming up or cooling down. It stops, -- irrespective of temperature -- on most engines when the sump level is low enough, even though oil pressure is maintained.

Lawrence Slater

As you like to carry out experiments, can I suggest a hopefully simple test to prove or not that oil viscosity and its draining properties when cold cause the issue.

Drain the sump when cold - heat the oil (could be in an oil can in boiling water etc) and then refill - start engine and see if the problem still occurs.
Would probably be better to fill twice so initial heated oil could preheat the block as it runs to the sump.

Only problem I see is not burning yourself !

Just a thought.

Or find an F1 oil heating system as used for gearboxes etc!


richard boobier

"Or find an F1 oil heating system as used for gearboxes etc!" I was thinking along those lines Richard. They warm the oil in Siberia and the likes, so why not kent? lol.

As a first test, I think it will be easier to insulate the timing cover and change my stat. But really I think all this is symptomatic of the "real" problem. Which I think has to do with the camplate and or front cam bearing.
Lawrence Slater

<<It happens as the engine (oil) reaches a certain temperature>> Does it? Proven?

I understand there is a delay, but how do you know this is temperature related. Could the delay not be the time that the chaincase takes to fill to the top level so that sucking can start?

Different, though related question.
How long does oil take to warm up? My impression is that it is really quite a long time. Someone with an oil temperature gauge would be able to add information.

I understand that most of the heat going into the oil is actually generated at the bearings, by the oil film being compressed. Its the very high pressures on the oil film that generate the heat. This being rather more significant in oil temperature than heat picked up by the oil as it flows through the oil galleries in the (warmed up) block.
Guy W

sorry I don't think the Castrol will quieten the box as it's the same viscosity as the Comma - the Castrol gave better gear shifts and I'd imagine to be more robust and longer lasting so better for the box
Nigel Atkins

<<It happens as the engine (oil) reaches a certain temperature>> Does it? Proven?

Well number one, it doesn't happen in warm weather, when the oil is already above a certain temperature. And as I said, once warm it stops happening. The converse of which is that once a the correct "cool" temp is reached again, it starts again.

I'll relate this yet again. I was in Andorra. It was hot in the town. No oil sucking at all, even from cold start. I drove up to the top of the Pyrenees. It was bloody cold up there even in the late summer. I was up there for about an hour. The engine got stone cold. On the way down, with cold air blasting through the rad the oil sucking commenced. It's definitely temperature related, but it's not temperature per se that causes it.
Lawrence Slater

Yes I understand the point about it happening when conditions are cold, not in warm weather.

The bit I was getting at was whether the time lag before the blue smoke cloud appears was dependant on the time for the oil to start warming up, or if it was a function of the time delay to fill the chaincase.
Guy W

Wow, what an amazing saga. My old Morris only had a CV breather from the top of the rocker cover and it went into the side of an oil-bath filter. When I changed to a cone filter, it just went to atmosphere and I never had any trouble with it at all. I then found a backing plate for the cone filter that had a vent inlet so connected to it. Why not just go the old fashioned way? There should be very little CC pressure if all is well with the engine so all you need is a route for it to escape.

N.C. Nakorn

N.C, with respect, you've missed the point.

Lawrence, Malc and others know there are a number of "solutions", be it a catch tank, open vent, change of carb or vent to the air filter. All of which mask the problem and none of which "fix" the cause.

What Lawrence is attempting to prove is the one or more deviations from the original design which results in an engine sucking oil. Only when this is fully understood and repeatable can he truly say "I've fixed it!"

I, for one, applaud his efforts and resolve in his endeavors and if I can add assistance along the way I'm only too happy.

best of...
M McAndrew


"It happens as the engine (oil) reaches a certain temperature, be that warming up or cooling down."

Is it not more correct to say it happens when the oil is below a certain temperature? As a result the volume in vs the volume out becomes a factor due to the viscosity of the oil below a particular temp. As an alternative to the insulation on the case you could run a gallon of 10w40 or 0w40 which flows better at a lower temp whilst being similar at operating temp. See the graph here.

Q, does this only happen with new oil and at what approx mileage does it stop?

As you know, as oil "ages" it losses some of it properties, particularly shear. This results in a reduction of cold viscosity (we all know how thin old oil is) and hence less of a problem for you.

On your high oil pressure, assuming your gauge is correct and the valve is operating correctly, it suggests your oil galleries, and in particular your relief bypass, may be "undersize" and thereby acting as a restriction to the return flow (that's a stretch I know but something to check when the engine is in bits!). FYI my 1300 goes this high on new oil in the cold...... hence I change it at the start of summer and by the time the cold arrives it's not a problem....

Best of....


M McAndrew

"dependant on the time for the oil to start warming up, or if it was a function of the time delay to fill the chaincase."
I don't know Guy. Like I said, maybe initially the drains cope with the fill rate, and are then overtaken by the thinning oil "flooding" in. Which is why I wondered if the oil warming/thinning rate might be different in the affected engines. If so, then it wouldn't need a dodgy cam plate or cam bearing to cause the problem. It could be something as subtle as a change of thermostat coupled to a more efficient fan on the old style radiator. But then bob shot my fox by having the early rad and multi blade plastic fan too.

Clearly there's a period of time after the engine is started, in which the timing cover isn't flooded. During that time the oil is obviously colder and thicker. Then at the goldilocks point – quite suddenly – the oil gets sucked up. Malc drives through it. I tend to slow right down or go neutral and let the revs die, or even stop the engine. In both cases the timing cover gets emptied. Mine mostly through draining, and Malc's via being sucked dry. In both cases after the sucking has stopped, the oil must be sufficiently warm/thin to drain quickly enough. And if anything, I would think the fill rate has increased above what it was when the engine was first started and the oil cold and thick. Which tends to go against my theory of a "leaky" camplate/bearing, since it would get worse as the engine gets hotter and the oil thinner. However, since there are two drain holes, both larger than the camplate feed hole, perhaps even if the fill rate has increased, the drain rate also increases sufficiently to keep up with it. ?????? The trouble is, that so much appears to be contradictory.

Mike thanks for the vote of support. You summed it up nicely. J.

"Is it not more correct to say it happens when the oil is below a certain temperature? "
Yup I guess it is. So actually Richards experiment in reverse would be useful. Add stone cold oil to a hot engine and see what happens?

I used to run Mobil 1 (0-40) in my spare engine, and unfortunately that didn't fix it. I didn't run it to fix the oil sucking, but just because it was supposed to be so good. Then is got too expensive and I went back to 20-50.

"Q, does this only happen with new oil --- "
Good question. As I mentioned a while back this is interesting, because I don't know for certain. For the last ten or more years I've had an HIF on the current engine, and it didn't suck oil. But, during that time I ALWAYS changed the oil in the summer.
Two weeks ago I changed back to the twin carbs, and it "didn't" suck oil. The weather was still mild then, so I wasn't really expecting it to.
A week later I changed the oil. Still no sucking.
Then on the 1st cold day, the oil sucking started again.

-- "at what approx mileage does it stop?"
It varies. If I've been crawling along in traffic it can start in a shorter distance than if I've been on a clear road. I've never been able to fix it to an exact distance or time. What does seem consistent though is the temperature reading on the gauge. At the moment on this engine and with this particular temp gauge it’s after the stat opens at 160.

The oil pressure is odd if it's not supposed to be able to read over 60psi. I've got 3 engines all reading much higher, you've got one, and plenty of other all report high oil pressure. Could all those engines have blockages somewhere? I think there must be a mistake somewhere about what the gauge is actually reading. Pump pressure vs oil gallery pressure.

I'm not sure if you know the full extent of the saga. Have you read the 414 + 128 posts in the "engine breather" and "good news bad news threads"? Not to mention several others concerning PCV that ran this and last year. LOL.

Lawrence Slater

Trying to get some definite links:

Is the high oil consumption ALWAYS in combination with the cloud of smoke shortly after starting the journey?

Or can there be smoke but no high consumption?

Or can there be high consumption but no smoke?

Richard Wale

Hi Richard. It's not an issue of high oil consumption. Apart from when the oil is being sucked into the inlet, via the pcv valve or the y piece, oil consumption is normal. The engine only "consumes" oil in this sudden burst, on cold days, when the engine is started from cold.

It was colder today than it has been, and the engine started sucking the oil sooner than in the last few days.
Today I managed about 1.5 miles before it sucked up oil. I started the engine, and it sat on my drive for about 3 mins at a fast tick over on choke. (I got distracted by a neighbour). I then drove up the road and sat at traffic lights for a minute or so. I drove another ¼ mile or so and stopped in stationary traffic. I did a U turn and drove about a mile on a flat roads. The temperature had already reached 160 and the stat had opened. I slowed down to let someone out, and as I put my foot down, engine stutters and loads of blue smoke from the exhaust.

Tomorrow I'm going to try insulating the timing cover.
Lawrence Slater

Did I read correctly, 0-40 was sucked up just as 20-50 is? That's a bit unexpected to say the least.... 0-40 at UK cold (0-5 degC) is like water :)

You misunderstood my point on mileage. What I'm getting at is if the engine stops sucking oil as the oil ages eg after 2k or so? I 'm guessing that as 0-40 is sucked then old 20-50 will be also, right up to the scheduled change at 3k, correct?

I see your point about gauge pressure reading pump output as apposed to gallery relief. Certainly my gauge is on the input to the filter and there's very likely to be some drop over that. Just how much would need another gauge to confirm.

Best of...
M McAndrew

In an attempt to nudge this thread towards (a record making?) 400 contributions, I'd like to ask a question about the duration of the smoking (I've scanned this thread to see if someone has already answered my question but there is too much to go through).

From what has been said, the smoking starts shortly after start up (correct me if I've got that wrong). My question is when does the smoking stop - is it within a few seconds, after blitzing the throttle a few times, after the engine reaches full operating temperature or what?

Apologies again if this has already been answered.

Chris H (1970 Midget 1275)

Mike, I probably have missed the point; if the standard system works then all you need to do is return everything to standard, but, if the standard set up doesn't work, then a 'fix' will not make an improvement and one might as well use a tried and trusted set up. I'm fascinated by all the effort to solve the problem but wonder why it's worth all the effort.
N.C. Nakorn

NC, There is another aspect. The earlier A series engines ran perfectly well with a system that just vented to atmosphere as yours did. But as the power output and revs increase on the larger capacity engines then the crankcase pressures built up to the extent that a PCV system was needed.

So the extraction using manifold vacuum was introduced, and modified through several versions during the late '60s and early '70s. The fact that your MM managed perfectly well as you describe isn't really relevant for the later versions of the 1275 A series engine.
Guy W

Why do people climb Everest, or listen to David Cassidy for that matter? ;)

Yup I used Mobil 1 for years through the 80's, and come the cold weather, the oil sucking used to start. Also I don't change my oil at 3K. I leave it in for double that, I always have, and still the sucking continued. I see your point about the viscosity, but why do most engines run 20-50 and not get the problem?

I've never let it run on until it stopped. I slow or stop the engine and let the oil drain back. Suffice to say that it continues long enough to have sucked up 0.8 of a pint from Malc's engine. Mike drives through it. Essentially it stops when the timing cover is no longer full, and by that time, the logical assumption is that the drain rate at least matches the fill rate.
Lawrence Slater

David Cassidy? are you really that old ;)

Don't get me wrong, I wasn't suggesting 10-40 as a solution only as a means to determine a boundary point as to the fill no fill.

"It was colder today than it has been, and the engine started sucking the oil sooner than in the last few days"

Viscosity does have an impact even if it's just the time taken from a cold start to suck oil. A lower viscosity oil would drain faster and therefore, assuming the fill rate is the same (big assumption i know), the time to suck should be longer. At some point, with an oil of the right viscosity, the engine won't suck.

As of yet this doesn't explain why yours does and others don't and we're back to the two potential causes i.e. the fill rate is too high or the drain rate is too low! The fact that sump level has an impact on the drain rate I'm inclined to think this is more significant than the fill rate but it will need further investigation.

Over to you....

Best of....
M McAndrew

Ha ha ha David Cassidy.... Man that was a long time ago.... Well at least no one listens to that now on purpose anyway...I hope.
Steven Devine

For the record (pun intended), I don't and haven't listend to David Cassidy (willingly). My sister though was an avid fan, as were a number of my early gf's. As far as I can tell, he managed to induce a certain moistness to a part of their anatomy. I haven't climbed Everest either. I prefer such passtimes as finding out why my engine sucks oil. LOL.

"assuming the fill rate is the same"
Well logically, in all our engines, the fill rate must vary with engine speed, since it's regulted by the spinning camshaft, as well as the viscosoty of the oil. The drain rate presumably only varies with the viscosity of the oil.

The sump level is definitely a mystery.
Today, after insulating the timing cover, and then fitting a hotter stat, and testing for effect, I'm going to drain the oil to just below minimum and see if the oil sucking stops -- as I've experienced in the past and as others have reported.

But again we always come back to one salient point. Only SOME engines, suck oil in this way. All engines have the same sump capacity and most people fill to the max level on the dip stick. Most 1275 engines using either a PCV valve or Y piece don't suck oil. Most engines are filled using 20-50 oil, and they don't suck oil. The drain holes in all engines are the same, and yet only some suck oil.

The list goes on, for how much in common all 1275 engines have, and yet only some suck oil. So I'm still looking for that hidden factor, that only some engines have. I've got 3 1275 engines. 2 suck oil and 1 doesn't(Midget). When I stripped my spare engine I found two things that might point to a cause. One is a recessed camshaft front bearing. The other is a distorted camshaft endplate. So the first things I'm going to look at on the running engine when I strip it are the same things.
Lawrence Slater

wow, you changed Mobil 1 at only 6k-miles and you moan about me pushing too much servicing work, for me it's 12 months/12k-miles with Mobil 1

my wife went to see David Cassidy a few years back and said he was just so full of himself she'd never go to see him again

the previous thread on this subject was/is 400+
Nigel Atkins

Would just add that increasing the diameter of front bearing holes by 1mm should allow something like 40% more oil to drain. I'm surmising that with later pumps the capacity was increased and allowed greater flow - but the drain back rate through the front bearing has remained pretty much the same.
F Pollock

Regarding that last comment; for quite a while suppliers such as moss used to offer a standard and a high capacity pump option. And as they were pretty close in price, I guess most would just go for the high capacity one. Maybe it just became standard practice to just stock the one version.
Guy W

The pump rate of the 'high capacity pumps' from my experience is the same as the old star drive pumps as the manufacturing quality of the old ones appear superior (nothing new eh!)
Bob Beaumont

Guy, your point about earlier A series engines just venting to atmosphere and working fine is irrelevant as they dont vent via the timing case, it comes from the tappet cover.

Lawrence, probably totally irrelevant but following your point about cold air hitting the timing cover do we know if it affects both Sprites and Midgets as just thinking that some have different radiator grills which could let more or less cold air in.

T Mason

Well...almost 400

Im probably bowing out of this thread, it takes to long to scroll to the end, let me know what you find at the end....good luck

Yes david cassidy was bad, but shawn cassidy was even worse .... all that blond hair

Its no wonder star wars was huge, that was the olny way to escape the insanity of tiger teen beat magazine creations...well that and angle dust

But I was just as bad... at that age of 12 I was already losing a gallon a week in man cream to my jamie lee curtuis poster and new for a fact that chisty nichiols and I would live happly married ever after ....

((with jamie lee curtis chained up in the basemnet as our sex slave of

70s... good times

Prop and the Blackhole Midget

Trev, my comment was in relation to N C Nacron's message. And although the earlier breathes connected to the tappet chest, they were still relieving cranckcase pressure. The point I was making that earlier engines don't have the same requirement for a designed PCV system.
Guy W

Guy stole the 400 prize. LOL.

--- "increasing the diameter of front bearing holes by 1mm should allow something like 40% more oil to drain" -- .
Hi Fergus we discussed this before and I wondered if it would weaken the cap. Nobody answered though. Also, if increasing the drain hole size was to fix the oil sucking at "cool" temps, I wonder if the oil might then drain too quickly at much hotter temps?

Both of my oil pumps are orignal BMC supplied. They're 25+ years old. Could the capacity of the pump really affect this?

Nigel. I should have qualified that. One of the reasons I first changed to Mobil 1 was for the long service life. As you say 12k. I probably left it in for longer than that too. Then I swapped back to GTX, and finally now any 20-50 I can get cheap.

Trev. Midgets and Sprites are both represented in the oil sucking stakes. lol.

I doubt the grill makes a difference, but as it happens I took mine off today to do an experiment tomorrow. I've covered the radiator with card so that the front of the engine won't be blasted in cold air. Hopefully with these temperatures the engine won't get too hot too quickly. I also tried to insulate the timing cover, but there just isn't enough room.

I also pulled the stat to change it for a hotter one. However, it seems I already had an 82c(180f) stat in there. Which is odd, since my gauge shows it opening at 160f. So either the gauge is out or the stat is openking early. So I put a 70c(158) stat in (I didn't have a hotter stat than 82), and the gauge showed it open at around 145. So I'm guessing the gauge is reading low. Anyway it'll be interesting to see what temperature the oil sucks at now.

Then I'm going to pull the radiator and remove the fan blade. I'll control the temp then with my electric fan.

Lawrence Slater

400th! Did I? I never know how the numbers are going anyway and I certainly wouldn't bother counting!

As part of the equation relates to the speed of filling, then one would have to include the oil pump capacity as one(of many) factors which might influence the fill rate. By comparison the emptying rate would seem to have far fewer variables.

As has been mentioned, the oil pressure on the gauge is measuring the pressure very close to the main "Stem" of a branching system. And one must assume that the pressure diminishes progressively along the branches, depending on how fast the controlled leakage of oil (i.e. the relief of that pressure) is at the component being supplied. The only item downstream of the front cam bearing is the gallery feeding to the rocker shaft and rocker bearings. They "bleed" oil out, and the more oil they emit, the lower the pressure is going to be at the front cam bearing.

The converse is true - tight clearances at the rocker will maintain a higher back pressure on the system and enhance the pressure squirting oil out of the cam bearing. This should be fine as it is how the engine is designed. But if the gallery were blocked or restricted for example at one of the the right angle bends that could have an effect. And it is the sort of occurrence that might feature on what otherwise appear to be identical engines. Lawrence?
Guy W

A vague idea just came to me

What about moving the oil seperator canister to the fuel pump blob like on the
Mini A+ spares has those kits fairly cheap

Just cap off the timing cover and drill 3 holes on the side of the block for the mini A+ oil seperator


Prop and the Blackhole Midget

It seems to me that the issues are quite clear cut:

1) Oil gets sucked out if the level in the timing cover is such that it floods the breather.
2)The contributing factors to this are a combination of some or all of:
a) cold oil drains more slowly due to higher viscosity.
b) high oil pressure causes greater flow rate into the cover.
c) issues with the camshaft bearing and plate can allow greater volumes of oil to pass into the cover.
d) sump level sets the datum point so higher levels of oil in the sump are more likely to cause the flooding and subsequent blue smoke clouds.

My oil pressure was reading about 90 with a cold engine when the problem occurred. It also needed a "max" oil level - under the same conditions it was fine when near "min". I have no idea about the state around my camshaft bearing but my engine has been reconditioned (another contributing factor Lawrence has identified.)
I suspect that at best the oil level in the cover is pretty near the mark and that it doesn't take much to raise it sufficiently to flood.
Or is all that an over-simplification?
GraemeW (Kent!)

Another suggestion on how to get around the problem, no matter how good, just won't cut it! Get with the program and stick to finding the "fix" or Lawrence will be v.upset lol

Best of.....

M McAndrew

I thought it out of character for you to use expensive oil unless you could get better value for money out of it than using cheaper oil

I'm not sure if the old Mobil 1 was 0w-40 or not as I can't remember - I do remember it being £24 with a £4 Argos card given back, then there were umbrellas and fabric suitcases as it got more expensive and even a a Mobil confirmed history of its use in your car

I'm going to finally make up a rad blind this year so I'd be interested to know how you get on with that and its final size (assuming you're still running the 82 stat)

having had a 1969 'Sprite' that came with a Midget rad grille that I swapped at a show with a Midget that had a Sprite rad grille I can't say I noticed any difference - I the correct grille was such a tight fit that I can't even remember having to bolt it in

you'd have been pleased with my first effort at a rad blind on my BGT, Hammerite black painted cardboard, then someone leant me the proper made full rad blind with roll up opening and when I used it the car started to overheat, it had the wrong pressure cap on

my Midget runs so cold on on the gauge during winter that I thought about trying a template the full width of rad on the grille
Nigel Atkins

Hi Mike. :). Prop's idea has already been discussed, last year I think. And I said that if I can't find the base cause, I'll make that modification. I've already decided that when I get my sump off on the spare engine, I'm going to drill the holes and fit a blank, so that it's good to go. To that end I've already got another timing cover with a sacrificial breather canister. David Billington amongst others has already done this, but not due to oil sucking, just for better breathing I think. So in theory it should work. But i still feel there must be a "simple" answer to this. Everything's simple when you know the answer :).

Guy. What I was getting at, is that aren't the "standard" capacity pumps sufficient to satisfy the needs of the engines? A higher capacity pump won't mean that more oil is actually delivered, only that it has the potential to deliver it? But I've just been reading Vizard. He says that the early pumps were too low capacity, and BL standardised on a larger capacity pump around 1969. Could there be a connection here? Could the large capacity pump overwhelm the pressure relief valve, and maintain high oil pressure. Again according to Vizard, there's an "extra" capacity pump. He says Leyland sourced two different makers of pumps, and one of them has 20% extra capacity. He says it's identified by having a black steel facing cover. I'm pretty sure I don't have that, but it's easy to check on my spare engine.

As regards the rockers oil feed. I checked that last year. The oil passage to the block was clear, and my rocker shaft didn't look starved of oil. The current engine seems ok too, with plenty of oil on the rockers last time I set the gaps.

Graeme. I'm sure all you say is right, but can't help feeling that there's one factor more important than all the others. Fix that, and the problem goes away.

--- " d) sump level sets the datum point so higher levels of oil in the sump are more likely to cause the flooding and subsequent blue smoke clouds" ---

And this is a mystery. I'm certain it happens this way, but as yet it's unexplained. How does the oil in the sump, 5" below the drain holes, interfere with draining, or get sucked into the canister?

Lawrence Slater

Went for a drive. Radiator screened from the outside, all but an inch either side. I also have a cold 70c stat in the engine.

Result:. The engine still sucked oil.

It was a clear road so I got to the same test point( circa 3 miles distance) where it usually sucks. Interestingly, it sucked oil at a lower temperature than before. Gauge reading of 135/40 rather than 160 (colder stat in). It's a bit difficult round here to predict traffic. Sometimes I crawl along, and others no traffic. Today I covered the same distance in a shorter time,-- a faster everage speed. The engine had less time to warm up. So presumably the oil was thicker than before, but sucking commenced after pretty much the same distance.

Something else I noticed. Constant depression at the carb breather take-off? There can't be. There must be a significant lag before depression is restored. It started to suck oil as soon as I opened the throttle. I backed off, and the sucking stopped. I opened the throttle and sucking begins again. If I drive along, just maintaining speed, not accelerating, no suck. But as soon as I try and accelerate, sucking begins again. So although these are described as constant depression, it must vary to some extent. We discussed this before. Since it's the rise of the carb pistons that control the depression at the breather take-offs, I'm going to drain my dashpots, and re-fill with 3 in 1 oil for the next cold run.
Lawrence Slater

The post 1969 oil pumps were made by holbourn eaton, and are made of aluminium with a steel back, and held in the block by 2 rather than 4 set screws. Its all you can buy nowadays except they are made in India not birmingham!
Bob Beaumont

"aluminium with a steel back" --- That sounds like the oil pump Vizard is talking about in his description Bob.

If he is, and they are all 20% extra capacity, then that rules out the pump as a cause, since if that's all you can get, then most engines must have one, and most engines don't suck oil.
Lawrence Slater


"It started to suck oil as soon as I opened the throttle. I backed off, and the sucking stopped."

That's interesting. It sounds like your carb pistons are not rising as quickly as they should but why? Using a thinner oil should help.

Best of.....

M McAndrew

Yup 3 in 1 is way thinner than the engine oil I drained out of the dashpots. Frustrating thing is, I have to wait so long to be certain the engine is cold enough, to be certain of the results. Too warm and it won't suck oil.

Meanwhile, can some one talk vacuum. You have a source, say 20Hg at the manifold. Then you tap it equally, as in twin carbs. What's the maximum reading you would get at the butterflies on each carb?
Lawrence Slater

Lawrence, the reason you get a high vacuum figure at the manifold is because the engine is running fast, the pistons sucking in air and then you take your foot off the pedal. The butterfly snaps shut and the space in the inlet tract between butterfly and inlet valves is sucked dry!

Whereas, the connection to the carbs (whether twins or HIF) is taken off at the upstrwam side of the butterfly. So when you take your foot off the pedal the butterfly snaps shut but and the vacuum take off is isolated from the engine suction. On this arrangement, suction is greatest when at WOT, not at overrun as with the manifold connection.
Guy W

Just thinking again about the impeded drainage from the chaincase. I am not really convinced by this idea that the oil in the chaincase remains cold as the engine warms up. I think that the oil in the chaincase will be rapidly mixed by the whirling cam chain with any warmer oil coming in and the proposed temperataure gradient wouldn't occur.

But, what may be happening is that overnight oil inside the chaincase cools and drains slowly down through the two drain holes. The temperature drops and the oil becomes viscous inside the drain holes to the point that it stops flowing, plugging the drainage tunnels. Now when you start up the oil being pumped through into the chaincase is quickly warmed and flows more freely. But although it is being churned around it isn't being mixed with the semi-solidified oil down inside the drainage holes /tunnels. The only source of heat to the oil inside the drainage tunnels is convected heat from the block, which takes a while to penetrate downwards to the bearing caps at the front bottom of the engine. {;-)!

It may in fact be quite normal for engines to behave in this way, with the chaincase filling until it overflows back via the porthole, into the crankcase. But on the ones that do suck oil the flow in is that bit extra such that there is sufficient to still overcome the overflow through the porthole window.

Separate question now, but relating to the relationship with sumps filed to the max mark. How much oil is in circulation when an engine is running? i.e. not in the sump but in galleries, filter, chaincase and generally being flung around the place? What would the oil level left in the sump be if it were possible to measure it on a running engine?
Guy W

as you know the oil grade number, e.g. 20, covers a range

a while back I checked with the WD40 company that own ‘3-IN-ONE Multi-Purpose Oil' and they told me -
"‘3-IN-ONE Multi-Purpose Oil' is SAE 17, it is quite a fine oil.”

(not to be confused with ‘3-IN-ONE Motor Oil’ (blue label) which is equivalent to SAE 20)

after oil would it be dashpot spring(s) weight (i.e. blue or red usually)

Nigel Atkins

Cheers Nigel. I've got the multipurpose 3 in 1. Very thin. It's only in for an experiment. The pistons will have far less damping, and if the delay in lifting with thicker oil "is" causing the vauum to rise at the Y piece, this should alter that. It's not a cure so much as confirmation that my twin SUs are responsible for the resumption of oil sucking. As you know it wasn't happening with the HIF. Which is partly why I prompted the comments about vacuum again.

Guy. Yup I get all that about how the depression is transferred to the filter side of the butterflies. What I was asking was, how is the source of the vacuum "split" between two carburettors. You have for ease of discussion, 20Hg at the manifold. Then you "tap" it equally, as in connecting twin carbs to the manifold. Assume two "identical" carbs each drawing exactly the same amount of air in from the filters, and exactly balanced at the butterflies. What's the maximum reading you would get at the air side of butterflies on each carb? Would the vacuum be split to a momentary theoretical maximum of 10Hg at each butterfly?

As the butterflies open, the vacuum from the manifold, is transmitted to the insides of the piston chambers, causing them to lift. This allows more air through the air filters, below the pistons, and vacuum is maintained at a "constant" figure. Call it "x"Hg. You then tap the carb at the constant depression point (for the engine breather). Does each breather pipe see "x"Hg? And does this re-combine in the Y piece to create 2"x"Hg? If you had tripple carbs, would you see 3"x"Hg?

"-- overnight oil inside the chaincase cools and drains slowly down through the two drain holes.". -- I can't see that happening Guy. When the engine's hot, the oil is thin, and I would think the timing case empties completely, including the drain holes. In fact I showed as much with my spare engine experiments. I hand cranked the engine, and oil ran into and eventually out of the drain holes. It didn't sit there for hours, even cold as I reacall. It's easy to check that again.

I would agree about the higher block face hole doubling as an overflow, except that when the oil reaches that level, it's already flowing into the breather canister, whose entrance hole is lower than the block face hole.

"How much oil is in circulation when an engine is running? Good point. This further lowers the sump level. So instead of being 5 inches below the main cap drains, it's even lower, which it makes it harder still to see how the level affects oil sucking. And yet it does.

"== if it were possible to measure it on a running engine? == " That's pretty simple I would think. Put additional marks on the dipstick representing different levels of fill. Run the engine without the dipstick(hole sealed). Switch off, and immediately insert the dip stick. Measure the oil level against the dipstick.
Lawrence Slater

Guys, I've entered this thread very late as I've only recently joined the site. I've read as much as I feel able and have now become way too interested in the conversation :-)
Nick Nakorn

Lawrence, the question about how much oil is in circulation related to earlier thoughts about whether the crank "paddles" actually hit the oil surface. I am thinking along the lines that as soon as the engine has run for a minute or two, the oil level in the sump will have dropped by an appreciable amount because of the amount of oil in circulation. Just wondering to what that extent would be. I cannot imagine that the designers would want the crank paddles splashing through the standing level of oil in the sump at 5,000 rpm. You would end up with broken cranks! Or at least so much drag on the crank that the engine wouldn't rev as well as an A series does!

I still think that oil drainage from the chaincase could result in blocking those oil rain holes. Granted that when the engine is stopped and the hot oil in the chaincase is runny like water, it will drain out rapidly, leaving the drain holes and chaincase clear. But there will be left a slick of oil over all of the inside surfaces. Maybe only a few molecules thick, that will continue very slowly to drain down under gravity, maybe taking several hours to collect at the bottom of the chaincase as the temperature drops. On a cold night I can well imagine this becoming sufficiently viscous that molecular attraction will eventually prevent it from clearing out through the drainage tumnnels.

I was trying to consider whether the oil level in a full sump got anywhere near the level of the LOWER outlets of those drainage holes. I think they are drilled at an angle so the outlets at the crank side are lower so it may have been the link to high oil levels. But there is still too much difference. Probably the better part of 1.5" - 2" at a guess. So that doesn't help.

But oil will cling inside those drainage tunnels, held by surface tension. Remember the split pin in the clutch bellhousing? Oil held there will then further cool and become quite coagulated in low temperatures. Sufficient to block them for a while after the engine has started up again on a cold morning. And the bearing cap, relatively isolated from the sources of heat in the engine, will lag behind the incoming camshaft supplied oil which run in galleries through the main block close to the heat supply.
Guy W

"Probably the better part of 1.5" - 2" at a guess. So that doesn't help". Except that oil will be sploshing forward and back,in every situation except when the car is standing still. Imagine the oil in a dynamic condition accelerating and braking or even decending the Pyrenees in a 10% gradient. Then it would be easier to imagine oil reaching the drain holes.

"leaving the drain holes and chaincase clear". Well no, there is standing oil inside the cover - above the gasket line up to the level of the drain. Is this significant? I don't know, but add this to the dynamic sploshing in the sump and you could get a sealed situation - at least momentarily.

F Pollock

Lawrence, to prove the cold oil theory have you thought about heating the oil before a run? I'm thinking the old parrafin sump heaters or even better an electric heater or hot air gun under the sump.

T Mason

Fergus, my comments were specifically related to the process I was postulating for impedance of the drainage through the bottom holes. So in this circumstance oil wouldn't be sploshing around as I was describing a car left standing still on a cold night (starting a car from low temperatures was one of the "requirements" to fit Lawrence's facts.

And , I do see what you mean about the small amount of oil left in the very bottom of the chaincase, but being above the drain holes this couldn't be a source of drainage problems so doesn't impact on my theorising one way or the other.

How long are the drainage "tunnels"? About an inch or so? Cold, viscous oil in there would take a bit of warming before it drained out and released an accumulation of oil in the chaincase after start-up.

None of this is yet identifying the reason why some cars do, and some cars don't! I still think that bit of the equation relates to the rate of incoming oil and there is much more scope there for some cars to vary sufficiently to "tip the balance" and overflood the chaincase.

I still think there is a potential variation in the amount of oil pressure release (i.e.oil flow) out to the rockers due to either bits of crud trapped by the double-bend in the gallery, or possibly by slight misalignment of the 3 gallery drillings during manufacture of the head. Not enough to starve the rockers of oil, but a drop in flow rate of e.g. 20% wouldn't show in the amount of oil feed to the rocker shaft, but would have a significant effect in raising the pressure at the cam bearing.

Guy W

Forgot pic,so posting again.

Lawrence Slater

Oil sucking only happens on cold days, almost always in the autumn/winter, but occasionally on very cold summer days. And once the engine is warm, it won't happen. So I reckon that pretty much proves that the oil being cold is a factor. But it can't be the crucial factor, since ALL engines start with cold oil in the winter, and only some suck oil.
The entrance to the drain holes might be sitting just above or below the standing oil. But again, this is the case for all the engines and only some suck oil. all the caps are the same with the same size drain holes. Assuming they aren't obstructed, how can the drain rate vary? See pic.
Likewise with the oil level in the sump. I'm certain that it's a factor somehow, but why don't all engines with a full level of oil in the sump suck oil?

You can prevent oil sucking by pre-warming the oil, or by reducing the sump level, or by removing the suction. But these can't be the root cause, since these factors are common to ALL engines. There has to be something else in the oil sucking engines, that predisposes them to the problem.

I ran my Sprite engine with 3 in 1 oil in the dashpots today. It still sucked oil at pretty much the same place and time interval. There was a definite expected effect, in that I had a massive flat spot on accelerating, esp' when cold. But it wasn't enough to lower the suction at the breather sufficiently to prevent oil sucking.

I'm thinking that only those things that can vary from engine to engine must be considered. What are they?

Oil pressure.
It would be a good candidate if all engines with high oil pressure sucked oil. But they don't.

Even though I've discounted this before, could the oil sucking engines go through a transitional period when blowby is sufficient to resist the oil draining back into the sump?
Here are my Midget compression figures.
Cold. 1/185psi 2/190psi 3/150psi 4/190psi
Hot. 1/185psi 2/190psi 3/160psi 4/190psi
My Midget doesn't suck oil, but clearly there's an issue on 3.
Here are my Sprite compression figures.
Cold. 1/190psi 2/190psi 3/170psi 4/185psi
Hot. 1/200psi 2/205psi 3/195psi 4/190psi
My Sprite does suck oil. But is blowby a factor?

I have to refit my HIF to prove that it STOPS sucking oil when fitted. Then perhaps suction might be considered as a prime cause. BUT. Most engines have twin SUs and don't suck oil. All the HS2s must produce the same depression at the breather, since they are all produced to a standard size/design. My own has standard piston springs, and I've shown that reducing the oil damping doesn't stop suction sufficiently to stop oil sucking.

Timing cover oil supply.
Whatever the drain rate from the timing cover is, it must be the same on all engines, because the drain holes are the same size. But the fill rate could vary. So apart from oil temperature and pressure, what else might increase the fill rate? I keep coming back to the only significant faults I found on my other oil sucking engine. The front camshaft bearing being possibly too far recessed from the front face of the block, and the definitely distorted camshaft end plate. However. Unless someone else finds the same or similar, this doesn't prove anything. And may be yet another meaningless factor.

Guy, you just pipped me as I was about to post. OK. Localised oil pressure at the front camshaft bearing. It's as good a theory as any, but how to test it?

Lawrence Slater


"I have to refit my HIF to prove that it STOPS sucking oil when fitted. Then perhaps suction might be considered as a prime cause."

Could you do one more run before you put the HIF back on please? But this time with no air filter fitted.

I'm struggling to understand how a HS2 with a breather intake at the same point as the HIF sucks so much harder, unless the filter is restrictive (which yours shouldn't be).

The theory is that as the manifold vacuum hits the piston it rises to allow more air in until the pressure at the bridge is equalised to that of the carb intake. I accept there is a momentary drop in pressure at the bridge, the duration of which is controlled by the piston damper and the grade of oil used. However, the duration of this shouldn't be so significant that it draws oil up the breather. You've proven a change of damper oil makes little difference on your set up, although the piston would/should have risen faster with the thinner oil hence the flat spot/weak mixture. Therefore, the only way to maintain a vacuum at the breather intake/bridge is if a vacuum exits at the intake of the carb ie the pressure above the piston is equal to the pressure below and both are -ve to atmosphere (or crank case?). The only way you can have a -ve pressure at the carb intake is if there is a significant pressure drop over the filter. You could have a -ve pressure on the bottom of the piston if the hole in the carb body from the intake to the bottom of the piston is restricted (highly unlikely but an easy check).

I don't believe blow-by is a contributor to your problem as any pressure built up in the crank case, when the breather outlet is blocked, will find the easiest way out eg the vent cap, dipstick hole etc

One last thought. Could the air velocity in the HS2's be a factor? I'm thinking not as each one carries half the air loading of the HIF but perhaps someone with more teaching in the subject could comment?

I await the outcome of your test run....

Best of.....

M McAndrew

I think that the (low) suction at a HIF is not caused by "borrowed" manifold depression at all. It's caused by the venturi effect of the incoming gas charge passing rapidly across the end of the connecting tube, in much the same way that fuel is drawn up out of the main jet.
Guy W

Latest NON-result.
I drained about 1.5 or a little more pints from my sump yesterday and took a drive. The level was left just above minimum. It still sucked oil, but it happened later. This isn't not conclusive though, it could just have been the slow progress of the traffic I was in, moving the suck point to further down the road. Also I'm pretty sure it sucked less oil, judging by the reduced amount of smoke. But the weather was a tad warmer yesterday, maybe that reduced the oil suck?. What does this prove if anything? Not much. Others have already said that if the sump level is low enough it won't suck oil, and I remember the same thing from years ago. As a solution, it isn't one. I can't drain the sump to below minimum to stop oil sucking.

OK Mike, I can do that. I'll leave the 3 in 1 oil in, to exagerate the effect -- if any. But if the KandN's are causing extra suction at the breather, then I've wasted the money I spent on them all those years ago. lol.

Guy, are you saying that the HIF doesn't operate in the same way as the HS2, with respect to the breather take-off?

Lawrence Slater

No I don't think I am. Both have the breather suction connection on the upstream side of the butterfly and I believe that neither relys on using "borrowed" vacuum from the manifold. They both use the venturi effect of air passing through the cab choke to provide the suction. The greatest suction is at WOT, when the carb piston is fully open and the air flow through the venturi is at its greatest.

In both cases, there may be a slight vacuum suction effect for a short while when the butterfly snaps open but the carb piston is still down and is inhibiting air flow in. But it is only momentary as this same suction is what causes the piston to lift and allow more air in to equalise the pressure. It is therefore of no use in providing the required suction for the PCV system.
Guy W

I still believe that the amount of suction required to lift your column of oil is very little and therefore looking into the means whereby suction is provided at the car is a red herring.

I suspect that all 1275 engines will fill the chaincase under the particular conditions that cause the drain holes to temporarily block. The oil level in the chaincase will rise until it reaches and overflows back into the crankcase through the "window" opening. I suspect this is perfectly normal and may persist for some minutes on a cold morning until the oil thins and begins to flow out properly through the drain holes. So far this is still speculation, an untested theory. You were at one stage talking of adding a perspex front to the chaincase so that you could verify that the chaincase is indeed filling up, and to what level, which would provide the missing proof.

All that is then required to cause the "column of oil" suction is for some engines to be receiving oil from the cam bearing at a faster rate than was intended by design. This may happen on a percentage of engines and may even be occurring for different reasons in some cases, but giving the same result - too much flow in for a limited period of time.

So you then look for the variable factors that have an impact of oil flow in, and we have explored a number of possibilities. The most pertinent seem to me to be wear, bearing installed position etc which increases the effective orifice size at the cam bearing. Or factors which increase the flow delivery (pressure) to the cam bearing. e.g. pump rating, restriction to the onward oil leakage and possibly (though I don't see how) the oil level in the sump.
Guy W

Well another day, another test. Removed the K&N air filters, and took another drive that resulted in more oil sucking.

Not much left to try bar stripping the timing cover off for a look.

Next test tomorrow is an 88c stat. I didn't have one the other day so I tried going colder with a 70c stat. That seems to have lowered the temperature at which oil sucking commences, to circa 140f. So we'll see what an 88c stat does.

Lawrence Slater

On your last points Guy, and going back to comments made by a few people regarding oil spec, I've been giving some thought to just how many engines might be potential oil suckers, and I've concluded that maybe it's all of them.

These are warm weather cars. Most people bought them for that purpose and probably serviced them in the warm weather too. I'm wondering if someone who's 1275 engine with a conventional PCV connection doesn't suck oil, were to change their 20-50 oil in the winter, it might start to suck oil too.

Regarding looking into the means and amount of suction. I wouldn't be bothering if my HIF sucked oil, but as it didn't i figured I try and see if something might vary the suction on the HS2s. Of course it will moot if when I re-fit the HIF the engine still sucks oil. And that takes me back to changing the oil in cold weather.

So I have 2 further tests in mind.

1). Put my old oil back in the sump and see if the engine still sucks oil with the HS2s.

2). Put the HIF back on with the new oil.
Lawrence Slater

Installed 88c stat and engine still sucked oil. But, it definitely sucked it earlier.

So since the cold stat delayed the sucking, and the hot stat brought the point forward, I'm again wondering about the oil being cooled in the timing cover, and hence slowing down the draining. When I felt the block it was much warmer than the timing cover. With the engine allowed to get hotter before the stat opened, the oil got warmer sooner, allowing more oil to flow into the timing cover sooner. Meanwhile the timing cover was still almost cold from the air blasting in against it, thus cooling the oil. Eventually the oil in the timing cover warms up and the oil drains more quickly.

Putting the HIF back on again tomorrow if the weathers dry to see if it still sucks.
Lawrence Slater

Given the amount of mixing taking place in the chaincase with the timing gears and chain whirling around, I doubt very much that this is relevant. The chaincase oil will very almost instantly become as hot as the oil being delivered into it, and although the metal cover of the chaincase will take longer to warm up (therefore feel relatively cool to the touch)the oil inside will be much warmer. Given also that the oil will become runny with only a relatively small rise in temperature I doubt that this is the mechanism limiting drainage.

My earlier proposition about oil trapped, stagnant and isolated from the hot incoming oil source is, to me, a much more convincing explanation. Oil being caught and held within a drain hole of that size is also a known and tested phenomenon on these cars.
Guy W

When I drained my oil the engine was hot, but the sump oil was still pretty cool. It was draining out so slowly that I stopped it and ran the engine for longer to get the oil flowing. But anyway, even if it does explain it even partly, it doesn't explain why all engines don't get sucking. Although as I wondered in my last post, maybe if everybody changed the oil in the winter, maybe there'd be a lot more oil sucking.

"Oil being caught and held within a drain hole of that size is also a known and tested phenomenon on these cars. " Is it? I haven't come across that.

Anyway there's an easy way to find out, I'm going to pull my timing cover and take a look next week if I can. I'm gathering the bits to fit a vewing window in the spare timing cover, and fit the radiator out of the way so I can run the engine on the drive for long enough to see what's going on.

This could make 500 LOL.

Hi Malc. Any news from you?
Lawrence Slater

"Not come across that" - Not been reading the clues then!
Guy W

Split pin in the bellhousing? I still can't see the drains inside the sump "clogging" up like that. I'll pour some cold oil into my spare engine drain holes tomorrow and see what happens. I still think the oil would all drain away when it's still hot, including the remains on the timing cover walls. I think if anything, it's the cold oil coming in on start up, that has the trouble draining away, but only because it can't keep up with an "over" supply.

Lawrence Slater

I put the HIF back on again today. NO oil sucking. However it was pretty mild today, so that might be the reason. If it doesn't suck oil though, the HIF must definitely have a lower vacuum at the breather than the HS2s
Lawrence Slater

This may have all been covered before and my capacity to remember it all has long expired, but is the problem nothing to do with the engine but the carburation arrangements. Mine did suck oil but doesn't any more. All I did was to change the pipe and filler cap.I can only surmise that was enough to alter the vacuum from the carbs. It seems that the problem is more acute with twin SU's than other carbs. This is no answer but are we looking in the wrong place?
Bob Beaumont

Hi Bob, that's exactly why I put my HIF back on again, to see if it would suck oil with "new" oil. It's still quite mild today, so I don't think it will anyway -- even if the twin carbs were still on it.

If it DOES suck oil though, then it rules out the carbs completely. But if it DOESN'T, then as you say, the suction level becomes more important again. It could be that ALL 1275's with a working PCV system, on TWIN carbs, are prone to it -- esp perhaps if they have an oil change in the cold weather. And if that's the case it's a design fault. It could be that the oil level in the timing cover is so marginal, that all it needs is a nudge to start oil sucking. Just a little too much suction and it sucks, and just a little less, and it doesn't. Your case is still odd though, although I agree the only things that renewing the cap and pipe would alter is the suction/crankcase pressure levels.

If it really does come down to marginal levels of suction, then it won't matter where we look, there won't really an "answer" that fixes it simply. It will have to be a modification, such as the additional breather on the side of the block off the fuel pump blank. Or ONLY change the oil in the summer. ;).

Having said all that, in my gut I still think it's a fault that can be fixed, and worth me experimenting with a clear inspection plate on the timing cover to see the actual level. And also comparing the cam endplate on my running oil sucking engine, with the one from my spare oil sucking engine.
Lawrence Slater

It was colder today, and the engine sucked oil this morning - WITH the HIF fitted. So that rules out carbs/suction as the main cause.

I can only assume that the reason mine hasn't sucked oil since I put the HIF on years ago, is because until 2 weeks ago, I was changing my oil in the summer. New oil in the winter seems to have pushed it over the edge.

So a possible solution to this is to fit an HIF, and only change the oil in the summer, hoping it's thin enough by the winter.

Next week I'm going to modify a timing cover to get a look inside.
Lawrence Slater

I wonder if the diameter of the drain holes is the same on all the 1275 engines? It's presumably possible that if this problem was identified at some stage they simply modified the spec and drilled the holes to a slightly larger size. Is the oil sucking on your early or your later car? Have you checked the sizes on both of your engines?
Guy W


"the engine sucked oil this morning - WITH the HIF fitted"

Well that's me a lot happier :0) I was starting to doubt the meaning of life LOL.

Onward to a new day and further testing...

Best of....
M McAndrew


I may be asking something that is in the earlier part of the post, but in your recent tests when the 'sucking' happens, how much oil is actually consumed?

Another confirmation, is the oil filler cap the vented type?

Richard Wale

Hi Richard. Could be as much as 1/2 pint, and vented. Read the whole thread please :). Otherwise it just gets longer and longer, with the same info repeated over and over again. I don't mind, but it puts some people off reading it at all. ;).

Guy. The oil is sucking on my current engine and my spare engine. Not the 1973 Midget. I can't date my engines to any accurate degree. One came in the car, and may not have been the original as it had no engine number, and the other came from a breakers yard, also no engine number. So The answer is I don't know, but I agree it's worth a look when I've got both apart. Meanwhile if someone has a stripped 1275, and could measure their front main cap drain holes, I'll compare to my partially stripped spare engine.

Note: I don't have any plans to pull the "1973" Midget engine apart, and anyway, that's a rebuilt engine, also minus engine number. So I have no idea how old that one is either. It may be the original rebuilt, or more likely an exchange recon.
Lawrence Slater

Well it was just a possibility. But maybe worth exploring. My 1971 engine has never sucked oil in quantity. Only ever done what I described as the oil phlegm version, - although that itself produces a pretty spectacular blue cloud, but without the excessive quantity of oil sucked.

Given that these cars were exported worldwide, and to colder places than (even!) Kent, it would seem surprising if the problem wasn't identified by BMC. And certainly it would appear that to go up one size in the drainage holes would have been an easy fix if the problem was indeed a design fault.
Guy W

Yup I agree Guy. But in the early '80s nobody at BMC oxford technical, or anywhere else I spoke to in BMC, had ever heard of the problem. So I'm guessing it was never corrected. Perhaps because it only happens to engines after a rebuild from original, which seems to be the case for whatever reason.

And opening the drain holes might not be possible anyway. I've asked several times if anybody has an opinion on doing this, with respect to weakening the main caps. I'm guessing nobody would risk it. There isn't that much metal between the shell and the drain hole to begin with to go upwards, and going downwards wouldn't help as much, as the lower section of the hole would be obscured by the engine plate. But when I get mine apart, it's one of the things I'm going to look at.

Hi Mike.
I forgot to add. With the twin SUs installed, on cold summer days, the engine would sometimes suck oil. The HIF is sucking oil now -- because I've put in new oil in the cold weather --, but 'never' sucked oil in the summer. So I still think there is less suction with the HIF, but clearly not enough to prevent it sucking oil in the winter with new oil. And if there was even less suction, it would defeat the point of having the breather connected to vent the cranckase in first place.

There must still be an underlying issue.
Lawrence Slater

As previously mentioned, it takes so little suction to lift the oil the height of the breather tube (probably less than 0.1Hg) that the difference between one carb set up and another is very unlikely to be significant.

The only time that excessive suction is likely to be relevant is on engines that have been incorrectly assembled with a breather direct to the inlet manifold and without a PCV valve installed. But that is an altogether different scenario anyway.

Lawrence, I remember you mentioning your contact with BMC technical during the 1980's, without any knowledge of this. But 15 years on it may be that they were no longer aware of such a minor possible modification.

I currently have 3 engines and will have to check the drainage hole sizes sometime. But, like you, I have no intention of stripping them down just to check on a whim at this stage!
Guy W

Ever since this first happened on my engines -- two of them, I thought there had to be others that it happened to, and that there had to be a simple and obvious reason that I just couldn't find. Then finally last year Bob started his thread, which prompted me to search the archives and find at least a couple of dozen more with the same description. Now we have Malcs thread, and mine sucking oil again. All of that bolstered my belief that a simple definitive answer could be found. Now though I'm begining to think that it's so marginal, that there isn't a quick simple answer after all.

I hope to pull the timing cover of my current Sprite engine this coming week, or the next. If I don't find a distorted camshaft endplate, or a gap under it similar to the one on my spare engine, that allows too much oil into the timing cover, then I'll give up looking and concentrate on adding a 2nd breather take off from the petrol pump blank.
Lawrence Slater

Lawrence, you have been to the world's end and back on this, and although you have eliminated many possibilities, you still haven't pinned it down to a single cause. The reason is that, as you have identified, it needs at least two circumstances to apply. One that oil drainage is restricted or prevented in some way, and secondly that oil feed into the chaincase must be excessive for some other reason. Combine the two and, together with particular ambient conditions, oil sucking occurs. That may not pin it to an exact physical cause, but it gets close.

One thing that I do find hard to reconcile, is that the overflow window back into the block doesn't prevent the oil level from ever reaching up to the breather intake. Compared to the two holes at the bottom which are normally sufficient to allow drainage,that overflow window is huge. How is it that it is overwhelmed?
Guy W

Have you ever heard of a show called "myth busters"? I think you might be shouldering to much responsibility for the cure of these engines!

Even Isaac Newton took the weekeds off!

“To myself I am only a child playing on the beach, while vast oceans of truth lie undiscovered before me.”

This cannot end without some scientific method of operation being proven man. We need hard evidence to support your Hypothesis before we understand how the blue monster is unleashed!

These 450 threads are screaming for resolve!

Carry on fellow knowledge seeker!

Steven Devine

Well, I'm beginning to feel slightly guilty for asking for help and then cheating a fix, before spending time on my Honda.

Leaving everybody, especially Lawrence, to reach 450 posts !

However, I have cold weather and time to start some real digging into my AHS problems.

I think an oil change then sump drop will be on the cards tomorrow, followed by dribbling oil through things.


Maybe I should have for the meaning of life !!
Malc Gilliver

If you compare a steel cap relative to a standard one you'll notice the drain holes appear lower down - and at a guess may be slightly larger too.

F Pollock

Hi Fergus, where does that steel cap come from? I doubt many people have them.

Steven, newton only had apples to worry about LOL.

Guy, -- "is that the overflow window back into the block doesn't prevent the oil level from ever reaching up to the breather intake." ----
Because as I've said before, the botom of the "overflow" hole, sits at a higher level than the bottom of the entry hole to the breather canister. The overflow hole is also smaller than the breather entrance hole, and it sits pretty smack in the middle of the breather intake.

Looking forward to your results Malc. No need to feel guilty. This is all good fun. :).

Lawrence Slater

Hmm, without checking, I would have thought the window was lower, and certainly a lot bigger than 9/16". But I hadn't checked it so not arguing on that point. But at 9/16" it is going to take a whole lot more oil flow than the two small drainage holes and should prevent the breather hole from being submerged. As you have pointed out, that breather entrance needs to be fully submerged for the oil sucking to take place.

But maybe at this point, if the oil overflow window is spilling over, say at half to three quarters of its diameter, that is near enough for the effect of the rotating chain to lift a standing wave of oil high enough above that level to engulf the breather opening.

Also, if that window itself is blocked off by oil spilling back through it, then there is no longer an air inlet supply. And although there would still be a pocket of air in the chaincase, the induction suction would now be pulling the oil level upwards as it seeks to create a vacuum within the now sealed off chaincase.
Guy W

Well the next time you have a timing cover off, you'll see I'm right about the sizes and relative postions of the holes. :).

--- "Also, if that window itself is blocked off by oil spilling back through it, then there is no longer an air inlet supply." ---- Again, something I argued way back. If the block face hole becomes obscured by oil attempting to flow back through it, how will the crank case pressure equalise? It will push against the oil attempting to flow through the lower drain holes, AND against the oil attempting to "overflow" through the larger block face hole. If that happens oil sucking becomes inevitable. It's only stops when the timing cover empties sufficiently, either by stopping the engine, or by the oil being sucked into the manifold. Then when the oil is hotter/thinner, the lower drain holes can keep up with the supply of oil being fed into the cover.
Lawrence Slater

More steel cap comparisons - Left one is from KAD right is MED. The KAD one clearly has larger holes than the 1/4" UNF threads for the set screws - at a guess these must be 8 or 9mm.

F Pollock

Hi Fergus. Circa £126 for the front main cap. I just rang KAD, and they say the drain holes are the same size as standard. But I agree, in the pic they look much larger.

I had a quick chat about this, and although they hadn't heard of this particular problem, they do modify -- reverse fit-- the front camshaft bearing to reduce the oil feed/pressure to the timing cover. They do it because they fit twin cams in the head, driven off a dry runnning belt. But as they use the existing cam to drive the oil pump/distributor, they have to reduce the pressure on the front seal to keep the new cam belt dry.

So as they aren't that far from me, I'm going to get my knackered camshaft bearings replaced by them(circa 40 quid supply and fit) and discuss this option with them. They also confirmed my long held suspicion that my front camshaft bearing should be flush with the block face, as that's how they've always fitted theirs.
Lawrence Slater

<< It will push against the oil attempting to flow through the lower drain holes, AND against the oil attempting to "overflow" through the larger block face hole. If that happens oil sucking becomes inevitable>>

Nope. That is not the same as the point I was making.

If oil gets to the level that it blocks the overflow hole, then the crankcase pressure will exit by the route of least resistance. Which is out via the oil filler cap where there is no impedance to the airflow at all. It won't therefore be "pushing oil back" into the chaincase cover any more than at any other time.
Guy W

"If oil gets to the level that it blocks the overflow hole, then the crankcase pressure will exit by the route of least resistance."

I agree, SOME of it will. But only because the overflow hole is "blocked" by the oil attempting to flow into the crankcase. This would be just the same as if you taped a piece of tissue paper over the overflow hole. There would still be pressure in the crankcase, and all of it can't equalise instantly via the rocker cover. There would be pressure felt by the tissue paper, that tries to push it into the timing cover. And so too with the real case. The oil trying to flow into the crankcase, would feel pressure attempting to push it back into the timing cover.

If that wasn't the case, then there would be no need of a PCV system in the first place. The timing cover vent wouldn't be needed at all, as the rocker cover cap would provide all the venting neccessary. But the rear oil scroll proves that not to be the case. Block the hose coming from the timing cover, and the rocker cover cap isn't enough alone to prevent pressure building in the crankcase, and forcing oil out of both the dip stick and the rear scroll.
Lawrence Slater

<<If that wasn't the case, then there would be no need of a PCV system>>

Sorry but this is an untrue statement as well! The purpose of PCV is to LOWER the crankcase pressure WRT atmospheric. If just to maintain it at atmospheric or prevent it going much higher then I agree, a passive venting system works fine, but a PCV system is intended to do more than that.

But the whole process is a dynamic one that varies constantly as conditions change. What may be true at one moment may be quite different moments later, if for example, the revs change. So if there were a state whereby crankcase pressure ended up pushing against a flow of oil through the overflow window that was high enough to close it, there would just be a splutter of oil pushed back before it again allowed crankcase "air" to bubble through.
Guy W

Guy. However you choose to define the crankcase pressure, it's pushing on the insides of the engine. That includes the front face of the engine block, and anything blocking any hole in that section of the block, that might otherwise allow that pressure to equalise with the timing cover. Hence if something as soft as a wall of oil obscures the holes in the block face, the pressure from the insides of the crankcase will tend to push the oil back into the timing cover. It's obvious, and although no doubt you will now say it's not, -- it is! :). Meanwhile the oil continues to feed into the timing cover until it rises to completely cover the canister intake hole. If the oil wasn't at that level, air instead of a continous column of oil would be sucked up.

Equally obvious now, is that the larger hole in the block face, is really there only to equalise the pressure, not to overflow the oil, as considered amongst other things last year in the engine breather thread. The oil isn't expected to get to that level, and that's a "fault" if there is one, caused either by blocked drains or an over supply of oil. My holes aren't blocked and that leaves over supply.
Lawrence Slater

Yes dear.
Guy W

LOL :)

I think this will make 5 ton. ;).
Lawrence Slater

I hope to pull the timing cover of my current Sprite engine this coming week, or the next. If I don't find a distorted camshaft endplate, or a gap under it similar to the one on my spare engine, that allows too much oil into the timing cover, then I'll give up looking and concentrate on adding a 2nd breather take off from the petrol pump blank. pretty sure that was my suggestion like way back around the 100 mark....

god am I great or what ?

Check mini spares ....they have em


Prop and the Blackhole Midget

Except that it was already discussed last year in another thread Prop, -- Yup you're great :). But dinna ye count the chickens just yet, the fat lady ain't singing. LOL.
Lawrence Slater

Which oil do you use (no doubt the answer is buried above). What happens if you use a lighter grade?
Paul Walbran

Paul, I assume you mean in the engine, not the dashpots. But the answer for both, is 20-50. This doesn't cause a problem in most engines, so shouldn't be the cause of oil sucking in those that do. But of course it was my recent oil change(in cold weather) with new 20-50 that made my HIF suck oil. So quite possibly, a thinner oil might prevent the oil sucking in the winter. But I still don't really think that's the solution.
Lawrence Slater

But if thicker oil due to lower temperatures stopping drain-back to the sump is an issue, lighter oil is a simple solution. Original recommended oil was both 20W-50 or 10W-40 so it's hardly under-spec.
Paul Walbran

I said "might" prevent sucking in the winter. But as previously discussed, I used to use Mobil 1, and that was sucked up in the winter. I refer all further discussion of this to my earlier answers/posts in this thread. :)
Lawrence Slater

This thread seems to have finally run out of gas!
Steven Devine

Or is it oil? lol
Lawrence Slater

Lawrence, I have the answer - if it's a winter problem, maybe it's just that it's too cold where you live, move here or even warmer to our Aussie neighbours.
(One more step to 500 ... )
Paul Walbran

Is it just very quiet today, or have we all been banned? I cannot believe that everyone has run out of things to say about oil burning blue smoke! - How can that be!
Guy Weller

I think everyones afraid to post as we all know it was ths thread that threw the BBS into critical mass
Disk overload! :-)
Steven Devine

Just taking a break from oil sucking, to suck in some welding fumes instead, whilst I get on with the front wings, drivers door, bonnet and boot lid on the Midget.

But I'll be back to entertain next week or so I hope, with a viewing window in a timing chain cover.

I Wish I could move to OZ or NZ Paul. it's too bloody cold for my increasingly old bones in the UK now. lol. I've never really liked the winter, but I'm beginning to hate it now.

How do you people ooop north survive? Yup, I'm a southern softie. lol.
Lawrence Slater

Oh no they cried - It's back…

Finally got the timing cover, timing chain etc off and found the oil drain holes slightly blocked with gasket material.

I'd guess no more than 10 percent restriction, so to understand the oil levels, I made a template to position the core hole, camshaft and timing cover to breather and amazed to find them all about the same height.

So I assume the only issue is the drain holes which I am going to 'help' by removing the front engine plate and grind back as shown.

This picture shows the relative oil in/out of the cover, the next will show where I'm going to grind the front plate away as it obscures the oil drain oils a little.


Malc Gilliver

Where I'm going to grind

Malc Gilliver

Are you sure you want to reactivate this mega thread? 😊
T Dafforn

It's safe until Lawrence gets back!
What Malc says is no suprise. If the oil can't get down the drain holes either because thay are blocked, or too much is delivered or the oil is to thick to flow quickly, the breather gets submerged. If you connect that to the inlet manifold there is enough suction to suck it up and feed it into the combustion chamber. Result - blue clouds.

I'm sure this has been said many times before (but trying to check back removes the will to live) can the breather be cut off, the original holes welded up and a new higher position found?
Graeme Williams

Echo. Blocked holes, no drain. Self evident.

Not so sure that grinding there, will make any appreciable difference, since there is a "very" small lip to the front plate at that point, and it doen't obscure the holes. All these engines have the same lip, and NOT all the engines have the same problem.

However, as TESCO like to say. Every little helps.:).

I'd be more interested in a look at your camshaft retaining plate. In particular, if there is any gap at all, between it and the engine front plate, that oil might be seaping from, -- in addition to the amount that is properly delivered via the purpose made hole in the cam plate. That might cause over filling.

Lawrence Slater

I've removed all the front end, cleaned marked and filed the front plate.

To my amazement where the old gasket was just visible behind the front plate when on the engine, even after filling the plate back the new gasket was not visible at all and until I removed enough plate to 'see' all the of the drain holes did the new gasket become visible.

Because my engine was in a Marina I assume it has had the Sprite front plate refitted to enable fitting in the Sprite and I think the gasket might well be the issue.

I've smeared a tiny amount of sealant around the camshaft plate to ensure the right amount oil leaks into the timing cover.

Anyway sump off tomorrow for a rinse and check the oil pressure relief galleries before putting the car back on the road.


Malc Gilliver

I forgot you had a Marina engine Malc.

Is it different to a Spridget engine, where the engine plate lies adjacent to the drain holes? Looks the same to me, but mine's a bit cleaner than yours, so maybe I can't see the difference. :).

Did you detect a gap between the engine plate and the cam plate?

Lawrence Slater

Malc, you may have missed my question.

Did you detect a gap between the engine plate and the cam plate? Is that why you used a smear of sealant?

Of course, with the weather being so warm now, the oil sucking stops. Mine hasn't sucked oil since I got back to the UK 2 weeks ago. So any test of any mod's made, to see how effective they've been, is going to be inconclusive until the next frost.

I guess that'll be this summer then. lol.
Lawrence Slater


I didn't want to post unless I had something worth adding.

I did have quick look at the camshaft end plate and there didn't appear to be any gaps, but I decided to seal it anyway.

I think the Marina engine is the same as Spridget, but I have increased the clearance on the front drain holes, by filing the front plate back and then cutting the gasket to suit.

Having taken the car for a spin today it didn't suck but as you suggest, maybe it'll be ok for the summer.

I did however stare at the oil pressure gauge and it sits at 70 psi while driving, so I think the oil pressure is too high.

In summary (till the winter - lol) I believe the gasket on the front engine plate was obscuring the drain holes and the oil pressure pump is not releasing the excess pressure.

So next plan is new oil pressure valve, spring, then sump off and clean the oil galleries from the oil pressure valve.


I think the combination of poor gasket fit on the front plate and high oil pressure was the cause - but we'll see.
Malc Gilliver

70 psi oil pressure while driving is absolutely bang-on perfect. 60 to 80 is OK, 90 would be judged too high.
David Smith

Thanks Malc.

Yup I agree. 70psi seems about right. I get higher than that. If you're right about the 70psi in cold weather being part of the cause, then just how much pressure I wonder does it take to "overfill" the cover.

You only need to measure the pressure spring length. If anything the old one will be weaker with age. So as long as it's not too long, I don't see the need to replace it. But I guess they're cheap enough.
Lawrence Slater

Well famous last words...
As I commented in a previous mail, have set up the crankcase breather via the hif44 carb and timing chain cover..
All well and good.. had gone for a couple of short runs around town. Leaks gone all good.... or so I thought!
Went for a longer run and after about 3 miles.. you guessed it... plumes of blue/grey smoke out the exhaust..
Pulled over and pulled off the breather...
Smoke all gone..
Think I am going to fit a breather to the fuel pump blanking plate or rocker cover...

T Dafforn

What was the temperature that day?
Was this a run from starting the engine from dead cold?
Lawrence Slater

temperature of the day about 18 oC and yes was a run from cold..
200 yds from garage to filling station then about 5 miles before all hell broke loose!
T Dafforn

I cannot prove if this worked, but FWIW here are the before and after photos of my front plate grinding.


Malc Gilliver

and after grinding and cutting the gasket to suit.


Malc Gilliver

Yes, see what you mean Malc. Certainly should ease the flow. But it always comes back to the same point. If this was the cause, why don't all engines do it?

I still think that there is "killer" factor present, without which, all the other minor contributing factors if present, wouldn't lead to oil sucking.

That's pretty warm. I don't think mine has ever sucked oil when the ambient temp is that high. But as the engine was stone cold, the oil was obviously thick enough to have the (un)desired effect.

I've forgotten Tim. To what extent have you rebuilt your engine?

I hope to put my spare Midget on the road soon. Then I can pull my Sprite off the road, and pull the engine for comparison to my Spare 1275 engine. Since both of these engines suck oil, I'm hoping to find a common smoking gun.
Lawrence Slater

For me the 'smoking gun' was the gasket - the one on the car protruded past the front plate, covering more of the hole, but because it was old and oil sodden, impossible to photograph, the new gasket did not protrude past the front plate even after the first grind back, subsequently it did protrude as I took more and more metal off.

If you think about it, gaskets are replaced at engine rebuild time and when compared to the tolerances of the block and end plates provide a 'variable' that nobody would even look at unless they have experienced the clouds.


of course, next Winter when this topic reappears from the archive you'll all know I hadn't fixed it - lol
Malc Gilliver

Hi Lawrence
Relatively full rebuild.
Rebore with new pistons
New main and big end bearings
New cam including followers and end plate
New duplex chain and sprockets
New oil pump and head

Bear in mind that I am only 150 miles in and using running in oil.

Have added a breather in rocker cover. Seem to have good negative pressure in the crankcase now.
T Dafforn


I'm very interested in your 'fix' in-as-much as i'm currently experiencing the same'sucking' problem. I was wondering if you would be kind enough to share with us exactly how much you enlarged the drain holes, and how much you removed from your new timing gear gasket... thanks for sharing...

tom crause
Tom Crause

Hi Tom,

I didn't enlarge the drain holes at all - what I did was simply fit the front plate, using only the two screws next to the drain holes, compare the front plate to the drain holes, mark the plate with a felt pen and file the plate back, I kept fitting and filing until all of the drain hole is visible. I then reassembled the plate and front gasket and all the front plate fitting and marked the gasket where it covered the drain holes, and cut it back. I fitted all the fixings when marking the gasket to give me the best fit, if you just use the two fixings near the crank, the gasket moves a lot.

I did it this way to keep the metal and gasket removed to a minimum to reduce the chance of getting an oil leak from the now reduce sealing area.


Malc Gilliver

Hi Tom,
If you haven't been following this all at least 2 other long threads, --- are you sure you have the same symptoms? If you are. welcome to the club. :).

I note you didn't mention the cam bearings.
1). To your knowledge, have they been replaced?
2). I don't suppose you have a pic of the FRONT cam bearing.
3). If you're using running in oil, then that begs another question. How come the oil is slow to drain away? I thought that stuff was "runny" all the time, compared to new 20:50. This might alter my thinking on the fill/drain rate. When my oil is hot(hence thinner/runnier), even on the coldest day, the engine doesn't suck oil.
Lawrence Slater

Timed out before I added the end to my number 3.

3). If you're using running in oil, then that begs another question. How come the oil is slow to drain away? I thought that stuff was "runny" all the time, compared to new 20:50. This might alter my thinking on the fill/drain rate. When my oil is hot(hence thinner/runnier), even on the coldest day, the engine doesn't suck oil. So I would have thought that running oil would be less likely to produce oil sucking. Does this shift the emphasis to the fill rate, and hence the oil pressure again?
Lawrence Slater

Hi Lawrence
You are correct the cam bearings were not changed.
Sorry dont have a picky
T Dafforn

Tim, do you know for certain that this engine didn't suck oil before you rebuilt it? What's it's history? What is it anyway? 1275?

My gut has always told me (for the last 30 years at least) that there is a simple, single, easily understood cause to this. So I'm looking for the common factor that all oil sucking engines share. In the beginning, having 2 such engines, I was even prepared to accept that the common factor might be me. But 30 years later, with oil sucking being more common than it first appeared, I'm convinced that the multi-minor cause theory, is less likely than the single significant cause theory.

So I'm back to over-fill, -- never really left it -- and why that happens. I don't really buy the slow to drain theory. Of course if it was drained faster, the timing cover couldn't fill with oil. But filling happens before draining. If there wasn't a supply of oil it wouldn't need draining.

The only thing that needs lubing is the chain. A motor bike chain lasts a surprisingly long time with a relatively small amount of oil on it. Spridget chains run in a bath of the stuff. With the thrower on the crank, and the action of the chain itself, the timing cover doesn't need much oil in it to lube the chain. So for the oil level to even approach what we are calling the "overflow" hole ( but is more probably only intended to be the pressure relief to the crankcase) suggests that there is too much oil getting in the first place. So it's either a leaky cam front bearing/camplate or too much pressure.

Quite a few of us have high oil pressure. I also have leaky cam bearings/plate(s?).

And all of the above, is merely my invitation to Malc, to claim the 5th century prize for himself. :).

Lawrence Slater

I just wanted to see if anyone would scroll thur 499 comments to notice I took the 500 spot....

Do I win anything

Prop and the Blackhole Midget

I was going to that! I'll wait for the 1000 slot now.
Roly Alcock

Well that's stealing. It belonged to Malc really. LOL.
Lawrence Slater

Hi Lawrence
Engine was a 1275 from a morris marina. No idea of its history.
T Dafforn

So you and Malc both with Marina engines. So along with Spridgets, it could be then that oil sucking was more prevalent than was understood.
Lawrence Slater

Malc, one additional question... I was wondering if you were able to make all of your modifications with the engine still in the car... I couldn't quite determine if you were from your photos.
Tom Crause


Yes, ball ache thou !

I drained the coolant, removed the front grill, radiator, fan, water pump for access - but I think you could leave this if you want, I undid the engine mounts, lifted the engine with a jack under a block of wood under the sump (watch for the mounts fouling the steering column - not sure if that applies to your left had drive car) then the crank pulley (after removing the starter and using a crow bar (i think called a prybar in the States) to stop the flywheel turning,) then timing cover, crank and cam pulleys. Then engine front plate off, file it back and refit.

I did check and smear sealant on the camshaft end plate, not because it needed it, but Lawrence suggested it might be a leak path for oil and I no intention of doing this twice.

I have refilled the car with 6.5 pints (UK) of new 20w50 oil and although it is a knuckle shaving ass wipe job, but my car hasn't sucked oil, so currently a success….


Prop - you S.O.B., my post and you nicked 500 - lol
Malc Gilliver

"but Lawrence suggested it might be a leak path for oil"

Yup I did. That's because at least one of my camplates was deformed, and had a 3/4 thou" gap under it, along all 3 sides. I simulated the gap on one side with a strip of paper, and conducted an experiment. This pic is the result.

And here's a link(s) to a short video clip of the method I used. Cut and paste one of them into your browser to make it work. I have no idea why I can't make it work straight from here. Can someone tell me how?

Lawrence Slater

Does that work ? - nope, I think when you paste the link on to the forum, the word wrap messes up.

Grubby finger nails there Lawrence !!
Malc Gilliver

I think I ran out of time, the file name seems to have text that doesn't format correctly in the "timing cover oil feed" area - either spaces or underlines.
Malc Gilliver

Yup grubby nails, and I'd probably just eaten a sandwich with them too. LOL.

Aha. Good ol' tinyurl conversion does the job.
Lawrence Slater

This has been prompted by the "cam chain or belt" thread. Several times in that thread, it was noted that a timing chain can stretch over time.

Most recently Daniel Stapleton said,
"A chain will stretch over time and thus vary the cam timing slightly whereas a belt always remains the same."

This is true, and whilst I think it's not sufficient reason to fit a belt, it has set me thinking about the oil sucking issue again.

Quick recap.
Oil gets sucked into inlet tract via the breather on timing chain cover, because there is at a certain point in the warm up of the engine(or indeed cool down), too much oil in cover, and the drain holes can't cope with it.

Please ignore the effects of varying camshaft and ignition timing, as it's not strictly relevant to what I propose.

What actually happens when the timing chain stretches?
What else happens when the cam timing varies?
It's my understanding, that when the cam timing varies as a result of the chain being stretched, the camshaft is constantly "loaded" and "unloaded", in terms of the thrust on it.

As a result of the camshaft driving the distributor, the camshaft is thrust forwards against the camshaft retaining plate. The end float on the cam is controlled because the camshaft is held between the nose of the cam sprocket and the cam retaining plate. When the camplate wears (and indeed the nose of the sprocket), the end float increases beyond the specified amount of 'x'thou"(don't have figure to hand).

I have already shown that a gap between the camplate and engine plate will allow more oil to feed the timing cover than should. However, I also noted when doing that, that I had to hold the camshaft forward against the camplate. If I didn't, then more oil escaped from behind the camplate between the face of the camshaft journal and the rear of the camplate.

Now exaggerate this. Have a very worn sprocket nose, 'and' a worn camplate. The resultant larger gap(endfloat) might be sufficient to explain how too much oil enters the timing cover.

But you say. "I fitted a NEW" camplate.
OK. Did you also fit a NEW cam sprocket?
And how about the timing chain? Is it new?

Now, going back to something Guy said many moons ago, regarding the distinctive patterns on the 'main' thrust face of the camshaft retaining plate. Guy concluded that these are the result of "hammering", caused be the camshaft in the normal operation of the engine.

So here's my thinking.
Normal hammering and rotation gradually knackers the sprocket and camplate, and the endfloat increases. Most people just replace the camplate. Some replace the cam sprocket, and some replace the chain too. For my sins, I only replace what seems obviously worn. Whilst this hasn't resulted in a poorly performing engine, it may well be the cause of too much oil in the timing cover.
As the camshaft thrust is unloaded, the cam retreats into the block, and the gap between the thrust face of the camshaft journal and the thrust face of the cam endplate increases. At this point, the small oil feed hole in the camplate ceases to regulate oil flow into the timing cover, as the oil bypasses it directly by being fed under pressure through the bloody great hole in the middle of the cam endplate.

A stretched timing chain will exacerbate this, as instead of the camshaft mostly being thrust forwards, due to the slack in the chain, the camshaft will be allowed to move rearwards more, aided by the oil pressure attempting to do just that.

How's that?
Lawrence Slater

Correction, but doesn't alter my thinking.

"The end float on the camshaft is controlled because the camshaft endplate (which is bolted to the engine front plate), is 'effectively', held between the nose of the camshaft sprocket, and the thrust face on the camshaft front journal".
Lawrence Slater

Read the "first" of my last 3 posts, for this to make any sense at all. :).


This could explain why oil sucking is often triggered by a few moments on the overrun, when decelerating.

Camshaft endfloat is quoted as being 4-8 thou".

Well maybe, 8thou" is too much.
Maybe, that 8thou" gap behind the cam endplate, when the cam is unloaded, is just enough to allow the oil pressure to force sufficient quantities of oil into the timning cover, to overcome the drain holes when the oil is at the right "cold" temperature.

This could explain why this is often triggered by a few moments on the overrun, when decelerating.

I've always measured the endfloat, and as long as I was at no more than the 8thou" mark I was happy.
Lawrence Slater

Ah yes. But on my engine I replaced the camshaft thrust plate and sprockets with new items and it still produced a smoke screen.
T Dafforn

Well I did say it was a theory :). Until I get my 2nd engine apart, I can't match the theory to any facts. And unfortunately, I didn't measure the endfloat on my spare engine before I took it apart, and as an experiment, ground the thrust face of the old camplate to see if I could make it fit snug against the engine plate.

Did you measure you're endfloat?
Did you replace the timing chain?

As I wonder in my theory, perhaps the quoted 8thou" is actually too much. Perhaps even with a new sprocket and camplate, the endfloat may be at the top end of the 4-8thou" permitted.

And if the timing chain is stretched, causing "lash" it might allow the camshaft to back off from the camplate more than it would if the chain was still in spec.
Lawrence Slater

For Peter Burgess.

Hi Peter. This was an interesting comment you made on the cam belt thread.

"The Metro problem was 70s/80s and a factory balls up whereby thin oil was burnt like no tomorrow (maybe a clue about oil viscocity too)"

Do you know the nature of the balls up?

Malc and others have metro blocks, and it seems they too have the oil problem. So this may well be the answer for them.
Lawrence Slater

Marina Block here
Malc Gilliver

Ah sorry. Got my M&M's confused. lol.
Lawrence Slater

New chain as well.
Only part not new were the cam bearings.
T Dafforn

Hi Tim. I just found your first entry on this thread.

"As many of you may know I was one of the "afflicted" and initiated a mega-thread a few weeks ago.
In my case the cause was incorrectly installed oil control rings (Doh!). "

That's what explains yours then.
Lawrence Slater

Hi Lawrence
That was correct and then reset the rings and all.was lovely. Drove it for a while but was annoyed by the oil leaks from the scroll. Fitted the crankcase ventilation to the chain cover and got smoke. Now with the connection to the rocker cover all is well.
Cheers Tim
T Dafforn

I'm interested you your thoughts on my question...

I recently took the leap and pulled the timing cover to checked out the camshaft end plate and drain holes. (the Datsun 5 speed made this project a little more difficult, in-as-much as i had to disconnect the tranny and slide the engine forward to get everything out...

Now, after cleaning up the drainage, and straightening the camshaft end plate, i'm ready to put everything back together. But before i do that i wanted to put new chore-girl pads in the timing cover... I was wondering if anyone had any thoughts about how many pads should be used? Specificallyp, i was wondering if you could stuff too many into the cylinder???

thanks in advance for you thoughts...
Tom Crause

one more item...

does anyone think that a double sprocket timing gear and chain could be contributing to this problem???
Tom Crause

Hi Tom.
"and straightening the camshaft end plate," ---- Could you elaborate on that? If it's bent, you'll need a new one. And if it was bent, it would have been "leaking" oil.

As regards the mesh filter(chore-girl pads). You don't need to replace that mesh. Only clean it. As for how much you need, well it's loosely packed, and only 1 inch deep. See pic.

Hi Tim.
Yep got you. I re-read your posts. I missed the datail first time round. :(.
"Rebore with new pistons New main and big end bearings New cam including followers and end plate New duplex chain and sprockets New oil pump and head"

Did you measure the endfloat with the new endplate and sprocket?

Also, with your rocker cover breather, what oil filler cap are you using? And do you have the timing chain cover breather "T'd" into the connection to the HIF? Or have you blanked off the timing cover breather?

Lawrence Slater


My car has a double timing chain and sprocket, but I think most 1275's do.

I didn't add any mesh to the original piece, as I'm convinced that the oil suck is simply a full timing cover, once the oil level reaches the breather take off - it will suck.

Last year I did add a catch tank with sight level, so I can check for oil suck without clouds, see piccie and you can just see the shiny top of the alloy tank with the black hoses.

I've left this on simply so I can 'see' any oil suck without anybody else seeing it !


PS anybody taking bets on 600 yet ?

Add your comment

Malc Gilliver

Hi Lawrence
Using the plastic oil filler cap with the breather. Have blocked the timing chain cover breather.
All works well. No smoke and not a single drop on the floor after parking up. Think I may settle on this setup now.
Cheers Tim
T Dafforn

Hi Tim,
The plastic oil filler cap is fairly free flowing as regards air entry. I think you really need the sealed cap if your pulling the fumes up through the engine block. Otherwise a lot of the vacuum effort will just be sucking in fresh air through side vents on the plastic oil filler cap.

For better fume venting, you could also put an air filter on the "open" timing cover breather pipe. KandN make them for this, to allow filtered air to enter that way. The reverse of the normal setup.

You've gone back to the early a-series system, which was changed to the timing cover system, as the engines became more powerful. As you say, you don't have drips from the oil scroll, but that isn't the only(prime) reason for venting. I think it's main purpose is to remove the bad stuff, so that it doesn't contaminate the oil, and eventually ruin the engine.

I've given some thought to doing as I've described above, and wonder why it wasn't adopted to begin with. I can only assume that it's more efficient to draw air in at the rocker and fumes out at the timing cover, rather than the reverse.

Heading slowly but surely to 600 lol.
Lawrence Slater

Hi Lawrence
Think I may put a vacuum gauge on the timing cover vent on this configuration and see what vacuum I am pulling with this setup.
With regard fume removal the vent system was also probably there to reduce emissions.
In my case given that I will probably end up doing very regular oil changes i'm not too worried about contamination issues.
T Dafforn

Hi Tim.
My understanding is that venting the crankcase is for the benefit of the engine. Initially is was just vented to atmosphere. Later to make it more effective, and due to environmental issues, it was positively vented to the inlet in some way, which did indeed reduce emissions. I guess if you change the oil often enough it will help a lot, but I reckon you'll still have more junk in the oil than if you have an effective PCV system.

Having just rebuilt the engine to the extent that you have, I'd personally want a properly working PCV system. Which is why I'm still trying to fathom out why my engines suck oil when using one, and beginning to think that I'll never know. LOL. :).

You'll need a very sensitive vacuum gauge to be able to read anything at the timing cover pipe, with your setup. See earlier posts by myself an Guy from about 05 November 2013.
Lawrence Slater

Hi Lawrence
Which oil filler cap is it that gives more vacuum. I am wondering whether we have our nomenclature confused. Mine is black plastic and is the same as those fitted to metros. In the system I have I can feel reasonable suck at the timing cover vent. Given that there are no leaks and plenty of suck I'd have said that the venting was running reasonably well.

Thinking some more, if the pressure in the crankcase is less than atmos then the gasses from combustion that get past the rings must be being scavenged to the inlet?

Certainly better than venting directly to atmos which a number of the mini guys favour.

T Dafforn

Hi Tim,
I'm trying not to duplicate pics if I don't have to. So scroll down to mine and Nigel's posts, 30 October 2013 at 17:50:26 UK time, and 30 October 2013 at 18:34:12 UK time respectively.

Those are the relatively free flowing mesh vented plastic caps. They are designed to be used with the later PCV systems on the a-series. The other type of cap for the early system that vented from the rocker cover, and often just went into the airfilters, was a chrome cap with a very small pinhole vent.

I agree, if you have -ve pressure in the crankcase, due to how you have it connected, then it must be working. But given how little the HIF breather take-off "sucks", I wonder how you are achieving that by sucking on the rocker cover -- with a free flowing oil filler cap. They do offer some resistance, but not much. You only have to breathe or suck on them to see how little. They are designed to allow air to be drawn in, and sucked down the block to pull fumes through the engine: -- and perhaps to allow excess pressure build up(if it happens) in the rocker cover to escape to atmosphere.

Maybe your oil filler cap is more restricted than the types in the pics. If it's not the same as those in the pics, what type is it?

Lawrence Slater

Hi Lawrence
I think that although the hif doesn't pull to much vacuum it can pull quite a flow. I guess this may be because it creates vacuum using venturi ?
In the end I think good crankcase ventilation requires flow. So should be ok.
Cheers Tim
T Dafforn

Hi Tim,
My experiments with my twin HS2's vs my HIF, suggest that the HIF pulls less, and that was my conclusion for why my engine had stopped sucking oil (because I took off the HS2's and swapped to a single HIF). However, when I changed the oil this winter as an experiment (I normally change it in the summer), my engine started to suck oil again, even though the HIF pulls less vacuum. So I guess you're right, the HIF pulls sufficiently, and as long as the oil is viscous enough it's sufficient to suck up the oil.

But what you've achieved (proper ventilation of the crankcase via the rocker cover, with no obvious air flow inlet to pull gasses through the crankcase) is presumably not supposed to be possible. Otherwise, why did BMC stop what you are doing, and introduce the PCV system via the timing cover?

I think you might well be getting -ve pressure in the crank, but does it follow that you are extracting all the nasty gasses effectively?
Lawrence Slater

Hi Lawrence
I did a fair bit of thinking about sources of vacuum in the car given my issues. Direct connection to the inlet down stream of the carb produces vacuum from two sources. Mostly from the engine vacuum ( but this depends on the throttle position) but some comes from the venturi created by the air passing the open vacuum port. For this source the flow from the vacuum port is limited as too much and you weaken the mixture too much. My understanding is that the pcv should stop this as it closes when flow is too high?

The port up stream of the throttle disc on the hif produces vacuum by venturi as well as some vacuum caused by the restriction of the air filter. Both related to the rpm. For me importantly this source can provide a high flow as it does not effect mixture. In fact I assumed that if you blocked the air filter at 1000 rpm the flow would be 1275× 1000 / 2 cc/ min ( maths could be wrong I've had some wine :-). Now of course you would never do this!

Whatever it is clear that the pressure in the crankcase must be lower than atmos as the oil leads ceased.
As to why BL ddidn't go this way. No idea, but triumph used it on their 4 and 6 cylinder engiines.
Cheers Tim
T Dafforn

Hi Tim.
Assuming you've connected to the designated breather take-off on the HIF, you're connected to a point of "constant" depression. So it's just about the same no matter what the revs or throttle opening. On the HIF though, the distributor advance vacuum take-off, is on the engine side of the butterfly, and hence the vacuum can get to as much as 30Hg, albeit through a very small hole.

Where are you connected?

As regards my question about why BMC didn't draw crankcase gasses up through the block and out through the rocker cover on 1275 engines. I think I can answer that now. And it probably explains what you said about the triumph engines. My guess is that they might well have a different design for the extraction of crankcase gasses. But it doesn't really matter what they did to the Triumph engines, as these are A-series Austin/Morris engines.

Follow this link for a very good PDF on the subject of crankcase ventilation. It's been linked to before, but just in case anybody missed it.
"breathersystems.pdf" at ---

Here's a quote from it.
BTW, for "cam cover", read "rocker cover" on our engines.

"In any breather system the crankcase (where the blow-by gases are created)
is linked to the cam cover via either a chimney cast into the crankcase and
cylinder head, or an external pipe. This chimney has two functions: Firstly, it
allows blow-by gases to leave the crankcase to equalise pressure in the top
and bottom of the engine. Secondly, it gives any oil that may be being carried
along with the gas time to “drop out” and return to the oil pan under gravity.
Note that depending upon the dimensions of the chimney, the velocity of the
blow-by gases can be quite high. For this reason, it is bad practise to use a
cylinder head oil drain as a blow-by chimney, as the oil and gas moving in
opposite directions can interfere with each other –"

A-series engines don't have a separate chimney in the block to vent the gasses. I reckon that's the explanation for why BMC didn't extract crankcase gasses up through the block on 1275 a-series engines. More power, more and faster moving gasses being sucked upwards, would have interfered with the oil trying to drain down into the sump via the oil return galleries, that were being used to extract the crankcase gasses travelling in the opposite direction.

On the 998's and 1098's the crankcase gas extract was via the tappet covers on the side of the block. But to strengthen the block the tappet covers were eliminated on the 1275's, and the extract was moved to the timing cover. Fresh air is drawn in via the vented oil filler cap, pulled down the same route, in the same direction, as the oil returning from the rocker cover to the sump, thereby not opposing it. This air is mixed with, and collects the blowby gasses in the sump and crankcase, as they are pulled through the timing cover by the vacuum from the take-offs on the carbs or manifold.

I think to reverse the flow "completely", is to risk a build up of sludge in the engine, even though it definitely does solve the problem of oil sucking. However, partially reversing the flow could work, and still vent the gasses effectively. So if I can't get to the root cause of the oil sucking from the timing cover, this is what I'll try.

I'm going to tap the blank for the mechanical fuel pump, fit an oil separator canister, and extract the gasses from there, by connecting this to the HIF in the usual way. In addition, I'll fit an air filter to the timing cover canister, which will allow air to be drawn in from there, thereby assisting, not opposing the oil draining from the timing cover back into the sump. I'm not sure if this is really necessary to be able to extract all the gasses from the sump region, or if this extra air intake might cause too much of an "air leak". But I can always fit the air filter to a tightly restricted pipe to limit the air flow into the timing cover.

Others have done this before me, but not as I understand it, to solve the problem of oil sucking per se.
Lawrence Slater

Hi Lawrence
Had wondered about the route crankcase gasses would take to get through to the head. I wonder if the reverse flow will lead to oil accumulation in the head??

I'm taking the vacuum from the port on the side of the hif44.

Had thought of using the fuel pump plate as a vent. You can buy them from mini parts places. But thought I'd try the rocker cover first as it cost less and fitted with my experience of spitfire and tr6 engines.

Cheers Tim
T Dafforn

Tim, when I understood what you'd done, my first thought was this is the perfect way to solve the oil sucking problem, because it aids oil drain from the timing cover into the sump. I'd never considered it before because I just assumed without really knowing why, that the flow of air and gasses had to be down through the engine. But now I realise that if the block has an inbuilt designated route for the crankcase gasses to be extracted from the cam/rocker cover, it can flow upwards. Many engines it seems do have an inbuilt or external "chimney". Shame the a-series doesn't.

I suppose if enough oil is being pumped out of the rocker shaft, and it's viscous enough, it may pool in the top of the head above the valves. In which case there might be more risk of oil being sucked down the inlet valves. But I don't really know.

Yup I've seen those mini-spares take-offs, but the angle looks wrong, and anyway it looks simple enough to create something myself.
Lawrence Slater

I realize that you all have probably read way too much on this subject, but i thought that i should let those contemplating Malc's oil sucking fix (filing the front engine plate, cleaning out the timing cover drain holes, and sealing the cam retainer plate) know that it did not work for me...

After a week long effort involving: raising the engine, filing the front engine plate, making sure that the timing cover drains were clear, and putting everything back together, the carbs suck oil just like they did before the attempted fix...

So i guess my next effort will involve tapping the fuel pump port and pulling the crankcase vacuum from there...

Tom Crause

Sorry to hear that Tom.

What grade oil are you using and what ambient temperature did you drive the car ?

Malc Gilliver

20-50 Castrol, and the temperature was about 65 degrees...
Tom Crause

I'd have been surprised if it did work. There's a so far unidentified underlying cause. Why does the cover over fill with oil?
Lawrence Slater

I'm surprised, I've only run my car below that temp so far this year and I've had no oil sucking at all.

I don't understand why it fixed my engine and why it didn't work on Tom's, the only difference I can see with my engine is that is was from a Morris Marina, so a different oil filter in a different location, but otherwise I have no idea.

and Lawrence….

The reason the oil cover fills up with oil is because there is more oil flowing in than out ! - lol

Malc Gilliver

For what it's worth, it may very well have something to do with the viscosity of the oil in-as-much as the sucking stops about twenty miles into a trip after the engine warms up.
Tom Crause


I think that's a different issue to mine.

From starting the car, I drive 1.5 miles, the temperature just lifts of cold, then there is a massive cloud of oil smoke, drive for another 2 miles and the smoke is gone and all burning has stopped.

I fitted a catch tank and repeated the drive and I had 0.5 litre of oil in my catch tank, so I emptied the tank, drove the car again and had another 0.5 litre of oil.

I then filed the front plate and trimmed the gasket to ensure good oil flow and the car has not sucked oil into the catch again.

Malc Gilliver

"The reason the oil cover fills up with oil is because there is more oil flowing in than out ! - lol"

Well yes, obviously. But also obviously, the engines were designed with fixed sized drain holes in the timing cover. Unless blocked, they are not variable in size. What could though be variable, is the rate of oil flow in. When cold, the flow rate out is clearly reduced, but even though cold, because the oil is being pumped in under pressure, it could still flow in at a considerable rate, sufficient to overfill the cover.

Then as the oil warms and thins, the drain, which depends on gravity, catches up with the fill rate.

So as I have repeatedly said, there must be an underlying cause for too much oil flowing in. Be that either too much pressure, or too big a "hole" for the oil to flow through into the timing cover.

With nothing else being altered in yours Malc, I guess you must have had some kind of restriction to the oil drain. But looking at it, I can't see how filing the engine plate fixed it.

More experiments are needed. Maybe I'll get around to it soon. But at the moment, frankly, I'm considering if I even care much anymore. Maybe time to dump the Spridget era for good, and buy something decent. :-
Lawrence Slater

Just to be really clear, I haven't increased the size of the drain holes in the front big end casing, I just made sure there was nothing restricting flow into the holes.

I think, on my car the gasket was restricting flow, so in an OTT solution, I cut the gasket and the front cover back to make sure they didn't block the drilled holes.

Malc Gilliver

I just wanted to add a 'post script' to my most recent notre on this thread... Although Malc's suggested modification did not fix my 'sucking' problem, i did go ahead a purchase one of those fuel pump baffle units from Mini-mania, and plumbed it into the existing timing gear cover to carb vacume line...

After doing so i took the mighty midget out for a 100 mile shake-down run. Upon arriving home i found that the mighty midget longer sucks oil, or even leaks from the rear seal...

So i just wanted to let those who's midget 'suck' know that there is hope, and life can be good!!!!!!!!

Tom Crause

Hi Tom,

How much was the baffle? Could you post a pic of the unit you used? I can't get the mini-mania site to repsond at all.

" --- and plumbed it into the existing timing gear cover to carb vacume line... "

I understand that it's supposed to be bolted to the side of the block (where the mechanical fuel pump was), not connected inline with the timing cover breather. Surely fitted as you have, it's acting as a restrictor. The effect of which will be to negate breathing to some extent.

If you aren't leaking from the rear scroll as a result, all well and good. But extracting the pressure/fumes from the crankcase isn't just about stopping the oil leaks. It's as much about preventing the oil being degraded, -- which is why I'm so keen(obsessed lol) to fix the base problem, rather than try to find ways around it that might introduce other negative effects.

Lawrence Slater

Good news Tom,

Could you post a piccie of installation.

Malc Gilliver

Mini mania site back up again. Got this pic.

Is this what you used Tom? It's the only thing I can find on their site described as "Crankcase Air Breather Kit Mechanical Fuel Pump Mounting"

Lawrence Slater

Lawrence, yes the crankcase breather you show is what i used... I installed the breather kit and plumbed it into the line that runs from the timing gear cover to the carbs, so i am now drawing air from both the front and side of the lower engine...

I'm not sure why it worked, but can assure you that it does, because i just went for a second 80 mile trip this afternoon and the carbs didn't suck a drop of oil, and the garage didn't have a drop of oil on the floor upon returning...

Malc, i'll take a picture of the setup tomorrow and post it then......
Tom Crause

Hi Tom.

Yup that will work indeed. It's exactly what I've been proposing to do to mine for some time, if I can't find the cause of the overfilling of the timing cover. -- Except that I figured that item is a bit expensive. It's not on sale here in the UK, and shipping adds more to the cost. So I'm intending to make my own.

The reason I expressed doubt, was that before I found that pic, I visualised your description;

" --- and plumbed it into the existing timing gear cover to carb vacume line... "

I read that as, you had bought some kind of baffle and it was in serial in the same hose from the timing cover.

Clearly what you actually have is a parallel installation. The reason it works, is that you are in effect reducing the suction on the timing cover breather outlet, whilst still sucking directly from the crankcase to relieve the pressure therein.

I've wondered if it might function even better if the timing cover breather is sealed off completely, and suction applied only from the fuel pump take off. My only reservation is that I wonder if the timing cover pressure could at some point become positive, and oil might be forced from the front oil seal as a result. Keeping the timing cover breather in the circuit would prevent that.

The other method I've considered, is to connect the carbs to the fuel pump take off as you've now done, but leave the timing cover breather "OPEN" with a filter on the end. That way air will not only be drawn in via the rocker cover cap/filter, but ALSO in and down through the timing cover. This will AID the oil flow back in to the sump, since it'll be draining under gravity as well as being sucked back into the sump by the suction from the manifold. In the even that there +ve pressure did try to form in the timing cover, it would vent from the filter on the canister, -- much as it does in the same circumstances from the rocker cap.

Lawrence Slater

As promised i have attached a couple of pictures of my installation... The first is of the baffle and a small canister filter that i fashioned from some 1 inch copper pipe and a 'chore boy' pad...

Tom Crause

And then a picture of the plumbing... The black hose on the right of the picture comes from the fuel pump baffle and T's into the hose that exists the timing gear cover. The upper T hose then goes directly into the carbs...

I hope this might provide some relief to other who suffer from this dreaded condition...

Tom Crause

Neat that.

Pity it's already in situ Tom. I'd like to see how that baffle is drilled to keep the oil from coming out of the fuel pump orifice.

Don't suppose you feel like taking it off off for a photo shoot do you? lol

I take it the copper assembly, is a couple of plumbing fittings put together?
Lawrence Slater

Looks neat Tom,

In summary then, you can increase the oil flow out of the timing cover like I did which might fix your problem and if that doesn't work you can reduce the vacuum, by splitting it over more locations like Tom has.

So we have two fixes for the people with oil sucking problems - and it only took 550 posts - lol


BTW, I'm still gonna leave my catch tank on, you know, just in case…. !!!
Malc Gilliver


You can only increase the oil draining rate, if the holes were blocked or obscured, as yours could have been. Otherwise it doesn't seem possible to increase the flow rate of the drains. Unless you drill the main cap. Don't fancy that.

I've known how to get around the problem this way since before this thread. What I'm still trying to find out, is 'exactly' why it happens. Specifically, why the timing cover has too much oil in it at some point).

I can drill the block, but I'd rather find the cause and rectify that, -- if possible.
Lawrence Slater

Lawrence, yes my home made canister is fashioned from two 1" by 3/8' reducers fittings put together with a one inch close nipple fitting and filled with a copper scouring pad...

As for the baffle unit you will see that it is about 2 1/2" in diameter and about 11/4" wide. The picturee that you posted pretty much shows how it is constucted. The 3/8 inch pipethread is oriented to the the top of the baffle and come off the unit at about 11 o'clock. The rectangular hole (shown in your photo) is oriented to the outside of the baffle and is sealed with the old blanking plate. A smaller 5/8 hole goes all the way through the baffle (at the bottom half of the rectangle)and aligns with the fuel pump hole.

It's a pretty slick outfit, one the i swear by...
Tom Crause


I appreciate your desire to understand the problem, as you say, in my case the problem might just have been partly blocked drain holes.

In Tom's case there appears to be a different problem, by taking the pressure direct from the crankcase he is reducing the vacuum on the timing cover, he is also removing crankcase directly and he might be indirectly allowing the oil in the timing case to drain better as a result.

"From: Tom Crause Illinois USA on 27 April 2014 at 19:17:45 (UK time)
For what it's worth, it may very well have something to do with the viscosity of the oil in-as-much as the sucking stops about twenty miles into a trip after the engine warms up."

So I think the reason is simple, my engine needed to drain better, Tom's needed less vacuum - only an understanding of Tom's breather system may give you the answer for your engine.

Malc Gilliver

Hi Malc,

"something to do with the viscosity of the oil in-as-much as the sucking stops about twenty miles into a trip after the engine warms up."

Yup, I discovered exactly that back in the early 1980's. Except my engine(s)/oil warms up sufficiently sooner than 20 miles. (SE England).

Tom's problem is a classic example of the timing cover filling with oil, and not draining quickly enough until the oil is thin(warm) enough. It's the same problem. He hasn't introduced LESS vacuum, he's split it. Obviously zero vacuum applied to the timing cover, would mean zero oil being sucked up. Hence there must be a 'critcal' level of vacuum, at which point, -- when the timing cover is full enough -- the oil is drawn up into the manifold/carb. With Tom' set up the vacuum directed at the timing cover must be reduced.

What Tom has done gets --(it seems to, but is yet to be demonstrated in cold weather with fresh viscous oil, but I do reckon it should fix it) -- around the problem of oil sucking, reduces sump pressure, and also removes harmful fumes from the crankcase. No real argument about it. But it still doesn't identify the cause.

If I already had holes where my fuel pump blank is, I may well have already done the same thing years ago. But I don't, and many other engines that have the same problem.

Studying Tom's setup won't identify the cause. The problem ISN'T too much vacuum, it's too much oil in the timing cover. Finding out why, and fixing that problem -- if possible -- , seems to me to be the better solution.

I'll say again for the umpteenth time. If I can't work out why too much oil gets into the timing cover, I'll do something like Tom has done, and give up trying to find out the why of it all.

Lawrence Slater

Hi Tom,

Thanks for the description. Makes perfect sense. I'll get a block of ally or steel, and if I decide to give up finding out why, -- (likely lol), I'll make a baffle from your description.

I'm surprised nobody in the UK supplies the same thing that MiniMania sells in the US. MiniSpares for example. The UK mini forums are full of discussions about better crankcase breathing.
Lawrence Slater

Glad to be of assistance...

As to the question of why the time cover is filling up with oil, both Lawrence and Malc have stated (on a number of occasions) that this is the result of more oil entering the cover than leaving...

Simple physics would suggest that if you can not increase the rate of drainage (although Malc did with his fix of cleaning out the drain holes) then one must decrease the rate of flow into the case. The only way that i could think of doing that would be decreasing the size of the oil port in the cam retention plate...

While i personally didn't have the courage to attempt this fix, i think that it might just work...

Tom Crause

"The only way that i could think of doing that would be decreasing the size of the oil port in the cam retention plate... "

Hi Tom,
That takes me right back to my posts from way back in other threads. There are other variables, perhaps the most significant of which, might be the pressure (excess) pushing the oil through the cam retaining plate hole(s).

As far as I (we all) know, because I haven't been able to find a bona fide BMC description of the oil feed into the timing cover, the oil is delivered to the timing chain, 'primarily' via the oil feed hole in the cam retaining plate.

As you know from your own experience, sucking starts and stops as the oil reaches the 'right' thickness/thinness with temperature. So why don't ALL A-series with the breather connected properly, suffer from oil being sucked into the inlet tract? Most don't, but sufficient numbers do for there to be an identifiable cause -- if it can be found.

Without repeating all my posts, in summary:
On my stripped spare engine, I'd used a worn cam retaining plate. I examined it and found it to be distorted. Oil was seeping from the sides. I haven't yet rebuilt that engine to find out if a new plate will solve the problem. In addition, I believe my front cam bearing is set too far back into the block face. This would allow a greater quantity of oil to collect behind the plate. Maybe sufficient oil, under pressure, to force the cam back against the thrust from the distributor drive, and allow excess oil to escape into the timing cover via the large central hole in the retaining plate. My current engine also sucks oil. I happen to have a pic of the front cam bearing on that engine, and it too has a front cam bearing set back into the block face. When I strip it this summer, I'll also check on the state of the cam retaining plate.

The other thing both of my engines have in common, is circa 100psi oil pressure on cold start(summer and winter), which never drops much below 80psi over 2500rpm even when hot. Is this the cause of it all? Or is it the combination of high oil pressure, an incorrectly fittted front cam bearing, coupled with a distorted cam retaining plate?

And just to make it harder to fathom. I've copied threads from this board and others, in which posters describe their oil sucking problem -- exactly the same temperature dependant symptoms --, but report NORMAL oil pressure. !.

It's a mystery.

So it's good to know that, "WHEN" it finally defeats me -- it did back in 1983 when I first tried to discover the cause -- , I'll be able to connect my breather circuit as you've done, and hopefully before I die, I'll be able to drive a complete winter without sucking up large amount of oil. LOL.

We just have to go for the all time record now. 600. It's not far off :).
Lawrence Slater

My oil pressure, from cold, with new 20w50, tops out at 70psi, maybe your 100psi is a problem, it could indicate a blocked OPRV ?
Malc Gilliver

And mine was even less than that...
New Castrol 20w50 at cold is 60psi....
Tom Crause

Exactly as I said Tom, it's hard to fathom. Yours is one of a few posters who report the oil sucking syndrome, and have NORMAL oil pressure. Which is one reason why I haven't concentrated too much on trying to find out why I have high oil pressure. The other reason I haven't persued the high oil pressure theory, is that there are also plenty of A-series engines with high oil pressure and NO oil sucking. I have one sitting in my Midget. Always over 90psi on start and doesn't suck oil.

But I am curious about how the oil pressure can be so high, when the pressure relief valve is supposed to prevent this. It's still possible, that on my engines at least, that it contributes to the excess level of oil in the sump, -- as long as, the as yet unidentified underlying fault is present.

REPEAT. Standard length spring, valve NOT sticking, oil passage back to sump NOT blocked. As an experiment I removed the spring completely. The result was I couldn't raise the oil pressure gauge above ZERO. I also have THREE seperate oil pressure gauges, and all give the same readings (give or take a smidgen). So if they're all inaccurate, then it's by the same amount. Seems very unlikely.
Lawrence Slater


If the OPRV is standard, then the high oil pressure is function of restricted galleries or higher oil flow.

So either the machining in your block is undersize, or you have high oil flow.

Higher oil flow would be longer rotors, or different gearing driving the rotors faster than on my engine.

If nothing else, 100psi is robbing you of some engine hp.

Malc Gilliver

Hi Malc,
I haven't stripped the Midget, but I assume it's a standard oil pump.

On my sprite engines, I also have the standard pressure pumps. Both Concentric engineering I seem to recall. Both are years and years old (circa mid 1980's). The last time I built the engines I measured the lobe clearances, and as they weren't excessive, I used the old pumps. I've done that several times. I can't remember the last time I bought a new oil pump. In theory, with worn pumps, I should be getting 'reduced' pressure, not elevated pressure. So I've kind of ruled out the pumps.

That leaves the galleries. I agree it must be down to those somehow. But where? Ends aren't starved, else I'd have had knocking and wouldn't have made over 100k miles on the engines. Top end isn't starved, rocker shaft gets enough oil. Also, if the restriction causing high oil pressure was prior to the front cam bearing, then if anything, the timing cover might receive LESS oil, not an excess.

Or maybe the restriction could still be before the front cam bearing, and yet still provide sufficient oil to fill the cover, through my 'leaky' cam retaining plate/badly placed front cam bearing combo.

My intention is to mount my radiator/electric fan remotely, on long hoses to give me access, fit a clear window to my timing cover, and run the engine. I'm hoping I'll see some indication of how much and how fast the timing cover fills. I don't want to waste money on adjustable oil pressure relief valves, but I might buy a spare spring and cut it short to see what happens in the timing cover if I can reduce the oil pressure.

Anybody got an old (weak) oil pressure relief spring they don't want? ;)

Lawrence Slater

Not 'hands on' familiar with an A series OPRV, but can you just remove the big nut that holds the spring and fit a thick washer under and refit ? I'm guessing that adding washers would reduce the oil pressure - effectively 'shim' the spring length ?

Malc Gilliver

would work in theory. But I don't think there's enough thread length on the nut to get a thick enough washer in there. I'll take a gander at some point.
Lawrence Slater

You can replace the standard valve for a 7/16" ball bearing and when used you have to use a competition type spring too.
John Coldwell

Nothing wrong with the valve or the spring John. We were discussing how to make the relief valve adjustable.
Lawrence Slater

I've reactivated this thread for all those who want to go over everything that's already been said -- ALL OVER AGAIN.

Go on, knock yourselves out. Rubber gloves and home made manometers, It's all here.

Far better that you do it here, rather than bugger up a new thread.

Lawrence Slater

Bringing this thread to the top again, for those who wish to comment in the other thread, and can be bothered to inform themselves with all the previous discussions, comments, and eliminated theories before doing so.

But you should also read the following very relevant threads in the Spridget technical archives too. Anything you can think of is almost certainly to have been thought of, and commented on there. To keep repeating it all is tedious and a waste of time.

There have been plenty of other threads on the subject, since I first posted about this problem in 1998. But this is more current.

So please read THIS thread, and those below.

"engine breather". Last post 22 August 2013 at 21:40:59 UK time.

"To vent or not to vent". Last post 14 October 2012 at 13:06:42 UK time

See you in about 2 weeks. lol. --- If you read them thoroughly that is. ;).

Lawrence Slater

This thread was discussed between 29/10/2013 and 19/09/2014

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