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MG Midget and Sprite Technical - New oil leak at the back of the engine

My 1971 1275 with 116k miles on it started leaking noticeable amounts of oil at the back of the engine earlier this year. It’s gotten to the point I don’t want to take it to anyone’s driveway because of the drips it will leave.

I could use some help trying to determine what changed to make it leak. It’s probably always leaked a drop or two in my 19 years and 30k miles, but something is different. I’ve never had to add oil in between annual oil changes, and this year I’ve had to top it up at least three times, maybe adding a quart over 800 miles in 4 months. Doesn’t sound like a lot of oil, but the drips sure are noticeable.

The compression is good, in fact it’s surprising how close the readings were to 17 years ago, after valve work and new rings.

Vacuum is a steady 16.5”. Non-vented oil filler cap, and when I remove it vacuum drops to about 14 and the engine runs poorly and idle drops. Put my hand over the rocker cover and it recovers just fine. Pulled the oil dipstick a little bit and it has little effect. Remove the dipstick and idle drops a bit. Tube holder was loose at one time, but I use Teflon tape and seems to stay put.

Replaced the rear sump seal when I did some engine work 17 years ago. I haven’t yet gotten a good look in that area, but that’s where I assume the oil is coming from. Just using a dental mirror to look up there so far.

These are my questions (thanks for reading this far):
-- Am I supposed to do anything with the oil separator on the timing chain cover? The wire wool type material is there. Removed the rubber hose to the Y-pipe, light shines through all three hoses just fine, ran some Brakleen through all the hoses and it came out pretty clear.
-- I had the fuel tank out a couple of times over the past winter. Could I have disturbed something there? I’ll check these again this fall because I need to replace the sending unit.
-- I once took all the carbon granules out of the adsorption cannister and dried them thoroughly on a tray. That was probably 15 years ago. Is that something I’m supposed to do periodically?
-- I’ve had the engine out at least twice in 2018-19 to do gearbox work, and although I don’t think the leak started immediately after putting the engine and gearbox back in the last time, should I be checking something from that process?

I’d appreciate any suggestions.

I should also mention this weekend I used an engine degreaser and cleaned the engine well. It appears oil is not leaking from the rocker cover, the banjo
bolt for the tube that goes to the oil filter, or the little fitting for the oil pressure gauge.


Mark 1275

Mark
the first thing that stands out to me, unless it's a typo, you put you have a non-vented oil filler cap, and Y-piece engine breather pipe.

The Y-piece would normally go to the twin SU carbs, if are they're fitted.

The oil filler cap should be vented (and filter) and best to have the original plastic type as shown in photo rather than the chrome bling ones with smaller hole and not so good for breathing.

Do you have any extra USA plumbing/emissions or extra or different arrangement over what would be on UK factory cars?

The idle does drop off a little when the oil filler cap is removed, perhaps as your engine running and mixture is set with a non-vented cap it needs resetting with a vented cap fitted.

800 miles to a quart is a lot of oil loss to me.

I'd also suggest, as much as you can, going for more regular use on reasonable length journeys and the occasional (or regular) longer distance and/or blow out run (Italian tune-up) as 1,500 miles a year (average) isn't a lot.


Nigel Atkins

Totally agree with Nigel. A '71 car should have a vented oil filler cap, no other orifice allowing air into the crankcase and a breather pipe from the canister via the Y piece to the twin carbs. Other additions such as a catch tank are OK so long as this restricted one-way pull of air and fumes through the crankcase is maintained. This is essential to limit the oil loss through the rear crank "seal".

The fact that engine revs change when filler cap or dipstick is removed is to be expected as it allows more air to be drawn through to the carbs and weakens the mixture.

Get this right and it should reduce oil loss, but whether this is the full and only cause of your recent change in oil leakage is a different matter.

GuyW

US cars had quite different crankcase breathing arrangements.

Note items 1 & 4.

Dave O'Neill 2

Ah, I didn't know that. So instead of a slightly restricted vent on the filler cap, they draw air in through the absorption canister.

I wonder then if this is either restricting the air flow too much, or alternatively allowing too free a movement of air in, which would reduce the effectiveness of the suction in limiting crankcase pressure which in turn would increase oil leakage.
GuyW

Thank you, Dave. Your illustration shows it better than I could explain.

I'm not sure where to look for a change in my U.S. setup. I think the vacuum is there, and it used to keep the oil in the engine, but now it's not.

The next steps I'm considering are verifying the oil's actually leaking at the rear sump seal, and checking all the fittings are tight in the fuel evaporation recovery parts. And probably dry the carbon granules just because it doesn't hurt. But I'm not sure what else to try or to look at.

I agree, Nigel, I don't drive the car nearly enough. Good weather, top down, staying off the highways, and it's a short driving season.

Thank you for the responses.
Mark 1275

Whay not remove all that gubbins and blank all open ends off? Is it not a bit of a bodge for emissions control? - which being a bodge is not only useless over time as everything gets clogged up, but also is prone to oil leaks and probably also causes the engine to run less efficiently - both perversely being no good for the environment.
Oggers

Interesting thought, Oggers, but I will say it's worked fine for many years. Maybe I should temporarily disable the fuel evaporation portion of it and see if the leak decreases.

Do people clean out the oil separator thing? I read in the archives here about someone flushing theirs when they did an oil change. Is that a maintenance task everyone does periodically and I've just missed it?

Do those neoprene rear sump seals wear out? I haven't been playing close attention, but I think the leak kind of appeared quickly - over a couple or three months - rather than gradually. But I could be wrong.

Mark 1275

I hadn't appreciated that your engine was modified to have an actual neoprene seal fitted. I thought you were referring to the original scroll "seal". Yes, neoprene seals do wear out, and can do so after a fairly short lifespan - in terms of miles rather than years, that is.
GuyW

Mark,
there are videos on USA Midget system and cleaning the cannister on John Twist's University Motors YouTube. -https://www.youtube.com/user/Universitymotorsltd/videos
Nigel Atkins

Mark

Try removing it and see. You may see a performance improvement! I don't think you have much to lose as all these sorts of bodges are pretty ineffective and invariably create issues of their own.

In the past, I have restored a couple of US import motorcycles with all this emissions/feedback to inlet nonsense attached. Firstly they look a mess, secondly, they serve no real purpose other than throwing garbage into the inlet manifold - never a good idea - and thirdly they go wrong.

The default with all UK bike restorers is to rip it all out and end up with something like the what the designers and engineers intended, rather than paying a flawed type of lip service to equally flawed legislation.
Oggers

I see from the diagram that David posted, that the connection to the rocker cover is marked as a special "restricted connector". If this has been replaced with a standard connecting pipe then that would upset the pressures in the vacuum extraction system that should be controlling oil leakage from the crank. Worth checking for.

Other than that I rather agree with Oggers. Only I wouldn't immediately rip it all out. I would disconnect at the rocker cover, sealing both pipe end and the rocker connection. Then replace the filler cap with the restricted ventilation type and see how that then performs. At least it is then easily reversible if you don't like it.
GuyW

The semi-circle seal that fits in the sump is also available in neoprene, maybe Mark meant this? Need clarification.
David Smith

Yes, David, that's exactly right. My records show I bought Moss pn 297-645, which is a neoprene version of the semi-circle cork rear sump seal.

I haven't yet found the video on cleaning the cannister on the front of the timing cover, but I'll look this evening. I think I'm creating more confusion than normal with my posts in this thread, so just want to be sure: will the video show cleaning the oil separator cannister, or the carbon filter cannister for the fuel fumes?

I appreciate the ideas.
Mark 1275

Carbon filter, I can't remember now if it might have been on a B but the principles are the same if it is, and it was cleaning off the car anyway. There's a video of a run through on a Midget (might be 1500) and another on a B IIRC.

Like a gearbox the vids are in in there somewhere.
Nigel Atkins

To be fair to Mark, he did refer to it as a rear SUMP seal. Several times too! It was I, (and others) who mistakenly took him to be talking about a crankshaft seal leak! My apologies, Mark.

I can still remember my teachers saying that the most important part of answering an exam question was to read the question properly in the first place!

Sometimes I have found that SUMP leaks can be resolved by carefully retightening the sump bolts. You never know, you might be lucky and have success with just doing that!
GuyW

1971 U.S. spec does not have a vented oil cap. Venting is via the canister through a restricted vacuum port on the valve cover. The original valve cover should be retained as aluminum covers do not have the proper fitting.

Vacuum path is from the canister bottom though the upper connection to the (restricted) valve cover and through the timing cover to the Y at the carbs.

Be sure to clean the cotton filter in the canister. The bottom can be unscrewed for access to the filter and the carbon granules. The carbon does not seem to degrade but can easily be replaced with fish tank carbon granules. With the filter removed, you will see how the carbon can be replaced.

Blow-by would be the likely cause of oil leaking through the rear scroll unless it is indeed a pan or crank cork seal.
Glenn Mallory

The restrictor is normally in the vent pipe from the rocker cover.

Dave O'Neill 2

I do have the restricted pipe in the rocker cover. I'll open up the carbon cannister, dry out the granules and check the cotton filter. I did this years ago, but I don't remember the cotton filter.

Glenn, I'm not sure what blow by is. Isn't that what happens when the rings are worn? I could understand with 116k miles it could be happening, but wouldn't I see some smoke in the exhaust, and maybe reduced compression? I should also mention when I did the compression test I squirted some oil in each cylinder and retested, and the differences were negligible. (Can't explain how two cylinders actually dropped. Operator error...)

Cold
1 2 3 4
140 139 138 148

Cold with a shot of 20W-50 oil
1 2 3 4
144 135 136 152

(Copy and paste kind of scrambles the numbers from my table, but I imagine the meaning is clear.)

These were my numbers back in 2003:

Did compression test: 149-142-148-150, 1 to 4.

I'm surprised there's so little change. And I do figure how straight I hold the tester has something to do with the variation.
Mark 1275

This thread was discussed between 13/10/2020 and 18/10/2020

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