MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - Oil pressure drops with high RPM. Need help.

I'm at a complete loss and in desperate need of some help.

I have a full race 1380cc engine on the racing Sprite that I have recently rebuilt over the winter. Literally every thing is brand new other then the cylinder head casting, block, pistons and crank shaft.

The engine was built to the thou with the david Vizzard book as guidance.

The oil presure however hot or cold drops with high revs. Right down to 25/30psi at 7000rpm

Here's my findings below:

Cold revving
Good pressure 85 - 60.
2000 > 3000 rpm holds pressure / maybe drops a little
3000 > 4000 drops 5 - 10psi

Hot driving etc
All rev ranges pressure drops per increase in revs. 2000 - 5000rpm

Hot revving post drive
2000 > 3000rpm pressure increases 40 > 60psi
3000 > 4000 drops 5/10psi
4000 + drops further relatively linear


Tried different gauges, different oils, bypassing the oil cooler system and checked out the relief valve all with no luck.

All I can think of is faulty oil pump. Which is a new high capacity MED oil pump or a faulty oil pick up which is also new.

Does anyone have any thoughts as I'm at a complete loss.

Thanks in advance
J
J Shears

It sounds like some sort of flow restriction to me(stating the obvious I guess)
Possible--
Oil filter restriction- is it fitted with any after market type of filter conversion
OR
oil too thick-Have you tried thinner oil or just different brands-??

Apart from that , the oil pump you would think would be ok but a retriction in the pickup could be a possible

Not much help to you there but maybe------

When you bypassed the cooler did you go back to original plumbing or use one of the (possible faulty) cooler hoses----

willy
William Revit

I just wonder if the pump is cavitating. Is there any noticeable frothiness in the oil? Does the pickup have a gauze strainer that might be a bit restrictive for a high displacement pump?
Greybeard

Could it be the dipstick incorrectly marked or not seated in the right place? - leading to too much oil (frothing) or too little (starvation)?
David Smith

I'm thinking along the same lines as David. Have you looked in the rocker box when its doing this? It's not filling up and causing pump starvation?

Jim
J Smith

I'd really like to see a pic of the external oil lines and how/where they are plumbed, specially if it has a remote filter and if it has a remote or spin on filter is it a bypass or full flow type---------
willy
William Revit

And, if it is a remote filter, is it inverted with a stand pipe? If so, is the filter too short for the stand pipe? It might help to post some photos, as suggested.

Charley
C R Huff

The flow rate of the pump will increase with engine speed. This will result in more oil being around and about in the engine rather than in the sump, causing the sump level to drop. If it reaches a critical level the pump will be unable to pick up sufficient oil to meet the capacity of the pump and will start to draw in air causing pressure loss.
Graeme Williams

It sounds like a shortage of oil - can you try 1/2 litre overfull? Does it make any difference?

What relief valve are you using? The standard or the 'Cooper S' ball set up?

Richard
Richard Wale

I have seen, with a standard oil strainer, sump bashed in enough to restrict oil flow, maybe the new strainer is squashed on the sump or maybe the strainer fitted height is shallow and allows the oil to dip too low at revs and expose the pickup hole. I have seen on a few A series non oe goodridge style oil hoses and adapter plate fitted, sonmetimes the ids in these are quite a lot smaller than oe A series and I have seen pressure drop alarmingly at higher rpms. My mate keith Calver makes a good kit should you feel the need to upgrde your system from OE.
http://www.calverst.com/webshop/lubrication/cst3021a-%E2%80%93-oil-transfer-pipe-braided-stainless-steel-0-50%E2%80%9D-bore/
Peter
Peter Burgess Tuning

What pushrods are fitted? What dash size are the oil hoses. Is the oil temperature consistent for low and high rpm tests? + a lot of what everyone else says including looking inside the rocker cap when the oil pressure is low? How much oil did you put in it on initial fill and what make and grade?
Daniel

Im going with RTV gasket sealer has leaked into the oil passage ways
1 Paper

Bit one sided this-----------------feedback
William Revit

I'm interested in this because one of the local MASC members has the same problem.

Rob
MG Moneypit

If the oil level is correct and adding 1/2 litre makes no difference to the high speed pressure, I would suggest that the intake side to the pump is all good.

The oil pressure gauge take-off is from the main oil gallery, so wouldn't blockages after that only increase pressure, up to the relief valve setting?

I think I would make sure that both the main pressure relief valve and the filter head by-pass valve are working correctly.

What relief valve are you using? I had problems with an aluminium valve plunger that picked up on the bore in the block and scored the plunger - it did not affect the running pressure, but more serious scoring could allow it to stick, and not modulate the pressure correctly.

Equally the feed to the filter is directly after the pump. From a previous suggestion, I would fit the standard steel tube to the filter, by-passing the oil cooler, and see if that solves the problem.

Have you tried a different oil filter head? There is a 'by-pass' valve in the head, and if it operates at a much lower pressure than it should, would this cause a reduction in pressure?


Richard
Richard Wale

Did you replace rhe old plunger and spring woth a new spring and ball bearing?

That new kit from moss is an issue as the spring is to long

Prop
1 Paper

Thank you for all your thoughts sorry for the lack of response in answer to some of your questions I have attached images and responded below:
______________________
William Revit-
Oil filter restriction- is it fitted with any after market type of filter conversion
OR
oil too thick-Have you tried thinner oil or just different brands-??

Apart from that , the oil pump you would think would be ok but a retriction in the pickup could be a possible

Not much help to you there but maybe------

When you bypassed the cooler did you go back to original plumbing or use one of the (possible faulty) cooler hoses----

_______________________

The oil filter is fitted in the standard way with a Swift tune filter housing. The oil currently in the car is 10-40 and with 20-50 oil it shows the same issue. I bypassed the oil cooler by simply connecting the filter to the rear oil pipe feed.

_____
The relief valve is ball and spring type with a slightly stiffer spring.

_____

I have tried slightly over filling it and it didn't seem to effect the issue however it was only very slightly over filled. (mostly by accident when filling the oil)

_______________________________


Daniel, England

What pushrods are fitted? What dash size are the oil hoses. Is the oil temperature consistent for low and high rpm tests? + a lot of what everyone else says including looking inside the rocker cap when the oil pressure is low? How much oil did you put in it on initial fill and what make and grade?

______________________

Solid machined and heat treated Steel race push rods are fitted. Oil temperature is consistent and does not appear to hot or cold. The hottest the oil temp has got to was during a 30min race in mid 30Degree heat the oil temp was approximately 100. The oil is filled to the max mark with 10-40.

______






Thank you all for your help. I fitted a Horse shoe type baffled sump when building the engine and my current thought is perhaps it is restricting the flow at high rpms. My plan is to remove the sump and replace it with the old non-baffled sump. At the same time I will replace the oil pick up pipe with my old oil pick up pipe and remove the damaged mesh on the old pipe to help flow (reason for replacing it was due to holes in the mesh).

I spoke at length with the head technician at MED Engineering as I wondered if it was a faulty pump. He said they had never had issues with their pumps and wondered if it was a pick up issue or when the engine was line bored if it was line bored slightly too big. However I'm not convinced on this as I'm sure we checked the bore and also I think the oil pressure would be constantly low throughout.

It may be a week or so until I can get around to dropping the sump off but in the mean time keep your thoughts coming its all appreciated. I will try to keep the post up to date to hopefully help others in the future at the very least as it seems to be a fairly uncommon issue and difficult to get an answer for.



J Shears

Another Image as both images did not upload correctly

J Shears

Off topic - what's the logic behind connecting the unused heater outlet to the thermostat?
AdrianR

Adrian, common mod for race cars using the early rad. It takes v hot water from around #4 cylinder and sends it to the return to the rad for cooling. Some people splice it into the small top hose.
David Smith

I guessed that was the intention, but seemed to me that with the thermostat open then pressure would be equal across both ends of the pipe.
AdrianR

I agree with Adrian, the pressure will be equal, thus no flow from the rear of the head, where it is most required.

Would be better to connect the hose from the back of the head to the inlet side of the pump, as per later heater circuits?

We run Castrol 10W-60 oil, with a horseshoe shaped baffle in the sump fitted to our 1380, and no problems with oil pressure - hot (<=120°C) 40/45 idle and 65/70 at >2,000rpm.

Have you tried replacing the ball relief valve with the original design tubular valve and associated spring?


Richard
Richard Wale

I moved my heater hose connection (no heater) from the bottom hose to the top hose and my running temperature decreased by approx. 30ºF

That was with a crossflow radiator.

Plumbing the heater into the bottom hose is great for warming your heater up on a cold day, but if not using a heater, you're feeding already hot water into a hot engine without any cooling taking place.
Dave O'Neill 2

As Dave O'N says:

D Plumb

Are the push rods restricting oil drain down from the rocker cover back down to the sump? As others have said, have you looked into the rocker cover to see what the oil level is like when the oil temp is hot?
Daniel

Ok. I guess you would have to measure flow rate and differential temperature across the head/around #4 to see whether it works and as I've done neither I will shut up :-)
AdrianR

What part no. is that filter--???
William Revit

I've had trouble in the past with 'B' series engines with spin on conversions with restrictions in the adapter and also filters with no bypass valve built in
To check to see if it is a restriction on the suck side of the pump or if it is on the pressure side you will need to adapt a pressure gauge into the hose from the rear of the engine that goes to the cooler
If it's a sucking problem the gauge will still drop off like your gauge does now but if it's a restriction in the filter arangement the pressure on your test gauge will stay up while pressure in the oil galleries measured by your original gauge drops off
willy
William Revit

I have had the same probs as you Willy and first thoughts are he has a restriction not the pump and most likely after the pump. We have seen an engine with a cracked oil pick up which dropped pressure as soon as the crack was exposed but that was on hard race track bends.

I agree with line bore not being a problem as you say pressure would be low at low revs then rise with increased pump capability with revs.

It evidences classic 'hole too small' somewhere symptoms. After market pipes, filter adaptors, oil pick up pipes, if they are smaller than OE it is daft running em no matter what the 'experts' say at the places where they make em/sell em. We have had conversations along the lines of, the guy who designed it isn't in, never had a problem etc etc
One must bear in mind sometimes thinner pipes and tubes are cheaper thus more profitable. You also have to remember quality and compatibility of material considerations when moving away from OE pipes, adaptors etc etc A few of the pipes we have checked over have even smaller ID fittings at the ends of the flexible tubes that are already smaller than OE ID!!!!!

Peter

Peter
Peter Burgess Tuning

Just looking at it another way. Is it possible your bearing clearances are too big and centrifugal force is throwing the oil out - did you Plastigauge the mains and big end bearing clearances? Is it possible the pump is lifting of its seat and drawing air as revs rise, because the bolts are too long? Is it sluggish getting pressure on initial start up -
f pollock

Picking up on the 'hole too small' thoughts, you could drill and tap the pump outlet oil pipe banjo bolt head 1/8" NPT, and install an oil pressure gauge adaptor in it with a second oil pressure gauge.

If the 'new' gauge shows 'normal' pressures, and the 'old' one the reduced pressures you are currently experiencing, the problem is downstream of the pump, i.e. pipework, filter/head, oil cooler etc. If the pressures are more or less the same, it points either to the inlet side of the pump, or the pump itself (unlikely?).

Richard
Richard Wale

Have you tried a different oil pressure gauge in case the gauge is playing up when the oil warms up? Is the oil pressure gauge pipe soft and expanding unduly when warmed up and thus reducing the pressure seen at the gauge?
Daniel

Richard,

Why 1/8" NPT as 1/8" BSP would be a more common thread in the UK and in fact most of the world as BSP was adopted as the metric pipe thread standard.

Daniel,

The tube swelling would be worrying but I don't see it would have any effect on the pressure reading unless it was forming a balloon but then it would likely be on its way to immanent failure.
David Billington

David,

That was my belief as well, but I am assured by someone with the necessary thread gauges that it is in fact NPT, which is the American 'pipe thread' standard.

The difference for 1/8" is 27tpi for NPT and 28tpi for BSP.

Richard
Richard Wale

Richard,

Maybe that person wants to check again as everything I have seen and my own measurements indicate the contrary. I know of a few other cases where DIN standards are metricated version of British standards because the items concerned are ubiquitous.
David Billington

The water bypass works great and drops the water temp by about 15deg. I recommend it if your car runs hot. Mine actually takes a little while to warm up now because of it, but at full race speeds on a hot 30deg day it sits at 80deg without the fan no problem. If it gets a little cool I can just blank off the radiator with tape.

The car has oem unipart filter on it currently and all the hoses are 1/2bsp size and seem to be consistent in size. It's also a braided oil presure hose so it shouldn't be expanding.

Bearings have been plastigauged and are 2 1/2 thou the engine being a race engine is roughly 1 thou over max road as recommended by David Vizzard.



I managed to get a chance to change the ball and spring relief valve for the orginal plunger type and it did make a difference by about 10/15psi and made the oil presure much more stable. Now it starts dropping from 4,500rpms - 50psi down to about 42psi at 7000rpm.

I'm sure it must be a flow problem as everyone says. I'm away Over the coming days but on Tuesday next week 5 days time I will remove the sump / oil pick up and replace with the unbaffled sump and old pick up pipe to see if it helps the issue.

Thank you all again for the help keep the thoughts coming and I'll keep you posted.
J Shears

Right then folks, I don't want to speak to soon but I think I have found the problem.

I managed to take the sump off today and immediately I notice something that wasn't there before. A hole in the oil pick up mesh, it's clearly been rubbing on the bottom of the sump causing the problem right. Wrong....

On closer inspection there seems to be what can only be described as a 2p coin insde the mesh, yep inside! It's sat right up against the bottom of the oil pick up pipe thus blocking the flow other then where the pipe has the two small arches which obviously at high rpm don't allow enough oil to be picked up.

But what is inside and how did it get there? I cut open the mesh and pulled it out and it seems to be the blank which is stamped out of the metal which holds the mesh and has the pipe fed through. I can only assume it hadn't cleanly broken off and when racing and going over the curbs the blank has come loose and dropped in to the bottom of the mesh and then been sucked to the bottom of the pipe.

I'm yet to get a new pick up pipe and reassemble but I will be very very surprised if it's not the cause of the problem.

Pictures to follow
J Shears

The mesh cut open and blank removed.

J Shears

The hole in the mesh. As you can see it's at the lowest point directly under the pipe.

J Shears

The blank. You can see the mesh indented in to it from there it had obviously been rubbing.

J Shears

The pipe showing the arches which I think allowed enough oil to be picked up at low revs but not enough at high revs

J Shears

Well done on finding it.

Quite a basic restriction in the end but not one you'd think of, cigar to Willy and its smoke at least to Peter.

Fair odds on a faulty new part but finding which one is the chase, well done.
Nigel Atkins

Well done...i think,

What is the coin err blank from and how did it get there...id be investigating that heavily

Id think it would have to be put in there intentionally for some. purpose i cant imagine... lawerance. would be a big help right now...this ul his ally

Maybe its a "zppd" oil additive coin....haha

Prop
1 Paper

Well, that is a curious one, and most surely the problem.

Prop, go back and re-read the explanation. J says he believes it is the punched out metal from the upper panel of the strainer where the pipe comes through.

Charley
C R Huff

This will sound odd, but l think it is supposed to be there. The 'coin' is fitted over the end of the pipe with the arched holes around it so that oil flow into it is radial and not directly in line with the pipe end. The intention being to distribute the suction around the full perimeter of the wire mesh filter. Why else would the pipe end have the arched edges rather than being cut square.

But in this instance for some reason (bent filter, poor quality part, bent sump,?) the gauze has been forced hard up against the 'coin', crushing the arches to which it is fixed and reducing their effective sizes.
GuyW

Hi Guy

I think your right. I have a couple of pick up pipes and they have the 'coin' at the bottom of the mesh. Interestingly though I have one which has not got anything and there is no evidence of the 'coin' ever having been there. It may have come from a later engine perhaps. I recall my Longman built race engine had a bespoke gauze which had no 'coin'.
Bob Beaumont

I have had them both with and without the disc.

If you haven't already got one, I have a couple of pick-up pipes/strainers.
Dave O'Neill 2

Nice find--
You probably need to measure the depth of your new pickup when you fit it to make sure there is sufficient clearance with the bottom of the pan---
I'd be tempted to have a real good look at the end of the pickup tube and make sure the
'arches' are big enough--they need to be the size of at least half the diameter of the tube even if there is no blank in there---
If they're not you'll need to sweat the plate/gauze off and file the size of the arches out and then resweat the plate assy back on

willy
William Revit

Willy

Doesn't the strainer just unbolt form the pipe?

No need to sweat! ;o)
Dave O'Neill 2

Just to add to my previous speculation, it is also possible that the pipe, with the disc on the end of it, is intended to support the gauze against collapsing inwards when the pump is sucking, in which case the arches around its end are all the more important. I guess one could also drill some extra holes in the side of the pipe within the 'neck' of it inside the gauzed area.
GuyW

I think I recognise your fingerprints in those pictures. Didn't you do the Great Strainer Robbery?

I'll get my coat . . . .
Nick and Cherry Scoop

Guy

Drilling holes in the pipe could lead to sucking air instead of oil.
Dave O'Neill 2

Good point. They would certainly need to be near the end. It's difficult to know what depth of oil remains in the sump when everything is happening at speed!
GuyW

Dave
No sweat----------lol
Looking at the pics I saw that bronze in there and forgot it was a brazed flange with the strainer bolted on-
Easy job then, just open the 'arches" out till they are half round to the size of the tube and reassemble -job done
With this done, even if the pan gets dented or the strainer sucks up against it,it will still work.
I wouldn't drill holes in the tube for the reason you mention-----oil surge, air sucking
willy
William Revit

Yes, I confess - holes in the sides of the tube was a poor suggestion. I withdraw that idea!

I still suspect that the pipe has a function there of preventing inwards collapse of the strainer gauze which probably accounts for the 'coin'. It would spread the load across an area of gauze rather than concentrating the wear between a few strands of the mesh and the points between the cut-aways in the pipe end.
GuyW

Here's one I found in the garage recently.

No disc and the scallops aren't huge.

Dave O'Neill 2

So in the earlier pic ... there was a small hole the size of an ink pen in the strainer what was the purpose of that hole

I didnt have a coin in mine, i would have spent it...haha

Prop
1 Paper

The small hole in the strainer was caused by it bottoming out on the sump.

Interesting about the 'Coin' how some strainers have them and some don't. My old strainer certainly doesn't have a 'coin'. (I think I've coined a new term here)

I can only think that even if the 'coin' is meant to be in there with a high capacity oil pump and revving over 5,000rpm up to 7,000+ it can only be restricting the flow unlike a completely open pick up pipe. The arches don't seem as large as the actual pipe diameter.

I'm going to measure the two pipes and work out if one is longer then the other or a wider diameter etc and report back.

I've dropped of the big ends while the sump is off and number 2 has been starved of oil and needs replacing so its looking like the next job is to remove, strip, clean and rebuild the engine.
J Shears

Whats also strange is that the strainer was thoroughly cleaned and washed out before fitting and I didn't notice the 'coin' in there at all.
J Shears

But this is the second screen you've had with holes in the mesh. Given 1300 sumps are the same size are you running steel caps - deep enough to somehow lower the depth of the strainer, or when used in conjunction with the horseshoe baffle it's pressing on the strainer when you nip up the sump?
f pollock

Is there any chance the engine is strapped, as per a david vizrd modification (it holds the block togather by keeping it from flexing at high rpm), its a piece of machined flat steel that is placed on top of the middle /#2 crankshaft main bearinf cap, the cap is machined flat so the cap and the flat steel bar basically stuck togather cuz both surfaces are so smooth but both are bolted with togather into the main with longer stronger hardware

i strapped mine with a machined piece of flat steel across the #2 crank main and it disturbed the strainer / pipe placment and i had to massage the strainer /pipe to fit properly cuz the strap set up about and inch higher then the pre machined bearing cap...

So im wondering if yours is strapped and the strainer was never modified for the strap and thats why its rubbing on the sump pan

Just a thought

To fix mine as i recall i had to reshape and shorten the legs of the strainer and i think had to drill and tap 2 new mounting holes into the strap i dont think i sljpped the stainer mounting legs under the crank main cap new harware...or at least im pretty sure i didnt... i wouldnt recommend it

But yeah... look for that ...if the strainer legs were never shortened and there is a strap, it would answer some extra questions and probably not allow a squre fit where the strainer pipe connected to the engine and cusing a some what minor air leak at higher RPM like what guy was referancing by drilling holes into the pipe

Bottom line, that strainer took some abuse and got a hole punched / Worn into the bottom of it, the question is why, what is the culpret that cuased it, and will it repeat its self agian and ruin another strainer ?



Prop
1 Paper

Ps.. the strap also holds the #2 main crank bearing in shape and not allow it to become oblonged and out of round during high rpm

Sorry i forgot to mention that part also

Prop
1 Paper

Our 1380 has a centre main bearing strap, and the oil strainer/pick-up is modified, i.e. 1 leg shortened, to fit on top of the strap.

Richard
Richard Wale

The first mesh only had a very small hole and it was at the top in the side. I think it was caused before it went in to the engine and doesn't show signs of rubbing.

I've mesured the length of the current pick up and the pipe is 5mm longer then the previous one. Also the 'coin' is/was attached to the mesh and from my measurements it would have sat roughly 3mm lower then the bottom of the pipe. So it's obviously detached and been sucked to the bottom of the pipe. I also mesured the pipe diameter which is 13mm and the height/width of the arches and the arches work out to be almost 2/3rds smaller then the actual pipe diameter! So I'm still convinced it's the cause of the problem as that's quite a large restriction.

The old pick up without the 'coin' was the same diameter and also had the same diameter arches so other then being 4mm short the pipe themselves are identical.

The engine has a heavy duty 4bolt main cap as apposed to a strap as shown in the attached picture.



J Shears

I reckon you've found it, or at least something that was going to cause a problem
Refitting the original (shorter) pipe with the mesh repaired might be a plan
Was there a mark in the pan proving that the new pipe was too long
willy
William Revit

Yes there is a very slight imprint in the sump from the mesh. I assume that it was rubbing and has cause it to break off where the coin is tacked on. This picture shows the mesh imprint in the base of the sump.

J Shears

Stating the obvious but---
If the sump is the correct shape it has to be that the pipe itself being too long as the cause of the drama by jamming the mesh and coin hard up against the pipe-
Try offering the sump up to the engine by hand without a gasket and make sure it easily sits in place without rocking on the pickup tube/mesh--Then when you fit the gasket you will know there is a nice little clearance there
willy
William Revit

So just for claririty,

At some point, the orginal pipe/screen/mesh assembly was replaced with this current one which is a completely differant pipe/screen / mesh


So the answer is to order up a new assembly that is the correct one for this car/ engine,

easy enough...problem solved

Prop

1 Paper

Just removed the pick-up from my 948, and it has the coin fixed to the mesh - about 1/4" clear of the pipe - and quite generous arches.

For future researchers.
Nick and Cherry Scoop

Interesting thread. I have seen this little disc rattling around in the strainer, when stripping engines a few times. Never knew what it was for, threw it away and forgot about it.

Les
L B Rose

This thread was discussed between 17/07/2017 and 20/08/2017

MG Midget and Sprite Technical index

This thread is from the archives. Join the live MG Midget and Sprite Technical BBS now