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MG Midget and Sprite Technical - Rear main bearing oil seal - A-Series

Has anyone found the Morris Minor Centre kit to work? After 14 years I give up. The first time I built the engine I had a Speedi-Sleeve put on the crankshaft flange to ensure a good surface with the correct dimensions. It always leaked. I keep replacing the seal, to no avail. The last time, I polished the flange until I could see my face in it, and used expensive silicone sealant. I modified the aluminium seal carrier with extra screws to hold it tight to the bearing cap. For a month there was not one drop of oil on the garage floor, but then it started leaking again. The crankshaft is in perfect condition. I have a centre main bearing strap and a damper pulley, so nothing more I can do to minimise vibration.

I'm advised that the only real solution is to machine the bearing cap and rear cover (upper half of the cap) to tighten them up, and then line bore them to restore the correct clearance for the scroll seal. This will be expensive.

I have breathers from the rocker cover and lower cylinder block (old fuel pump point) going directly to the inlet manifold. Should I consider a breather catch tank?

Les
L B Rose

The crank flange may have been factory machined but it wasn't machined to be concentric. It wasn't until the Maestro 1.3 that it was machined concentric (and thicker) because it was designed to use an oil seal running on the crank flange.
If your crank is 1 thou out of concentric, in a short time the oil seal will wear and have a 1 thou gap all around and as it is quite a big circumference that will let a lot of oil past it.
Some have fitted crank seals and have had excellent results, some have had very poor results. I suspect the good results happen where the crank just by chance has a perfectly concentric flange.

Rob
MG Moneypit

Les,

Are you saying the polished face you could see your face in is what the oil seal runs on? That's not good as the surface may be too smooth and lead to seal wear, the surface should have some fine roughness and in production I understand they're plunge ground so the grinding marks are aligned around the surface parallel with the seal face. If the speedi sleeve didn't sort it then maybe it is as Rob mentioned a run-out issue which I expect could be addressed with a stop at a crankshaft grinder to have the surface touched up and made concentric. If the engine is out and the flywheel off then it should be easy to check the run-out with a DTI and magnetic base.
David Billington

Binned my MMC/Peter May seal after the first attempt. The odd drip (or even a lot of drips!) is better than the Exxon Valdez sized slick I had with the so called seal kit!
John Payne

It's a long time ago but I thought the machine shop ground the flange after fitting the sleeve. But I will check next time the engine is out. I didn't know about the concentric grinding in production. Surprised the MMC didn't mention it in the kit instructions.

I mentioned the cap line boring because I plan to rebuild the spare engine (which is actually the car's original) and have to decide which route to take. I have to do all the usual work on the block and that would be the time to do it.

Les
L B Rose

Hmmm....the machine shop says that closing up the cap will need a lot of metal taken off, otherwise the clearance at the sides stays the same. Looking at £260. I'm probably back to making the seal kit work.

Les
L B Rose

The spiral scroll is supposed to return oil into the engine and the lower cap is drained into the sump.

The problem with the seal kit is that there is no way for any oil that gets past the scroll to get back to the sump until it reaches a level that is higher than the seal lip.

So the seal has a build up of oil behind it and it leaks, usually worse than without the seal kit.

I have tried drilling additional holes from behind the seal but you are limited by the depth of the flange mating the kit to the main cap.

I did consider fitting a drain pipe from the bottom of the seal enclosure to the back of the sump but I didn't do many A series engines and most that did have the kit fitted had it removed later!
Chris at Octarine Services

Chris, you are confirming my impressions from reading many criticisms of this kit. I wonder whether I should build in more negative crankcase pressure, eg with a PCV valve. Maybe I should fit an oil catch tank plumbed into the intake on the carb, via a PCV valve? Before anyone asks, the compressions are excellent and there is no evidence of excessive blow-by.

Les
L B Rose

PCV valve is cheap and effective, worth a try.
We have had good success with XPAG oil leaks by retro-fitting PCV.
Being cheap, with expensive alternatives, it's worth a try.
Paul Walbran

Les, Some months ago there was an article in Mascot about an alternative approach to the commercially available crank seals. When I am back home I can check the proper reference to it.

The seal system commonly used is a conventional annular oil seal in a special housing. The criticism of these is that they are expensve and that the seal lip wears fairly quickly at the high revs of an engine crank coupled with some lateral flexing, at which point they fail.

The author's alternative was to use a face seal acting axially on the rear of the crank housing which is less prone to variation and should last much longer. The other advantage was that the system can be readily installed with a modification which is fairly easily made at home and likely costs of around £5.
GuyW

We have fitted around 8 of the Calver ST seals with no problems.
Peter Burgess Tuning

I have dug out an old PCV valve - the standard 1098 one, with a new diaphragm. This normally fits to the rear branch of the MG Metro manifold that I have, but I have this time connected it to the vacuum point on the carb. It seems more sensible than feeding oil vapour to only 2 cylinders.

Peter - I've looked at the Calver kit and it's much cheaper and obviously works quite differently. Do you have any advice about fitting it?

Les
L B Rose

May not work there Les. The port in the carb generally only gains 3 or 4 psi below ambient whereas the manifold port sucks much more than that. The advantage of the carb port is that it's suction increases the wider the throttle and higher the revs, which is when blow by will be greatest. The manifold port increases at high revs but mostly when the throttle is shut off, as on the overrun.
GuyW

The full manifold vacuum is not passed on to the sump as the pcv regulates it. If the pcv valve is faulty, then the engine gobbles a lot of oil. I haven't measured it, but I suspect the end effect of the pcv is much the same as the port on the carb.

But if you have the carb port, join it directly to the crankcase ventcrathercthan via a pic, that's how it's designed to work.
Paul Walbran

I had the PCV on the manifold for years and was still getting leaks. I then removed the PCV and connected directly to the carb - still leaking. So I have tried all permutations! Tempted by the catch tank but not convinced there is a plausible reason it would help.

Keith Calver says his kit is only for the 1275 engine.

Les
L B Rose

Paul, that's what I meant. The manifold vacuum is much greater so the PCV closes with the higher suction. If connecting to the carb the suction is very low so the PCV wouldn't operate (work) so is better just left out.

les, the catch tank doesn't improve the crankcase extraction to limit oil leaks. It simply catches and condenses oil vapour so it doesn't contaminate the combustion charge and lower the octane level as much.
GuyW

Hi Les
No specific advice. Drilling and tapping the retaining screws can be a little tricky.
Peter Burgess Tuning

Resurrecting this thread because I have the engine out. Years ago when I fitted the Morris Minor kit I could not get a good finish on the crankshaft flange, so the machine shop put a sleeve on it. I just found that the sleeve was standing still and the flange was merrily rotating inside it. It must have been doing this for quite a while as the sleeve is really loose now. So I'm off to the machinist again tomorrow to get a better job done. Hopefully with this rectified a new seal will do the trick.

Les
L B Rose

Well it's all back together now. £105 spent on getting a new sleeve put on the crank flange, nicely ground now so should be perfect. New seal installed with enormous care. New clutch plate of course, plus the usual gaskets and sundries. About £170 in total. Went for a 5 mile shakedown run. Result? Pool of oil on the floor, the same as before, possibly worse. I am getting too old for this.

To pre-empt the usual questions:

Compressions are 170 and equal.

PCV valve has suction. New diaphragm.

No oil mist from rocker cover.

No smoke from exhaust.

Oil pressure 60 psi hot.

If I had the money, I would hand over the engine to a specialist and say "fix this", but I don't.

Les
L B Rose

Les I am sure you have thought long and hard about all the possibilities. But, how about it being a leak from the oil pump housing?
GuyW

Fair point Guy, but the backplate has the soldered-on oil pump cover and there was no oil inside it.

Les
L B Rose

I have always assembled the rear main cap to the block with a smear of Hylomar. I still have the scroll on the crank but no significant oil loss. I also found the cork sump seals were better than the shaped rubber/synthetic ones at keeping the oil in.
Bob Beaumont

I agree Bob about the cork seals, which I have. Using the lip seal kit removes all the scroll effect, and the kit instructions don't mention using jointing compound on the bearing cap. The lip seal carrier covers the cap joint anyway, with sealant between.

I just thought of one thing. I have used the high pressure relief valve spring (with ball) for years, and have now reverted to the standard spring and plunger. Let's see what that does.

The reason for opting for the seal kit was that the previous engine leaked from the rear and I didn't want to take chances with the new engine. How wrong can one be? It's all so frustrating, as in every other respect it's a lovely engine.

Les
L B Rose

Les,

Do you have one of the long USB inspection scopes that you could poke in through maybe the starter aperture to try and verify where the leak is. You would need a suitable smart phone/tablet/PC/laptop. They only cost around £8-£9 off ebay. This sort of thing https://www.ebay.co.uk/itm/114396355739 .
David Billington

Bob's mention of using Hylomar between the rear main bearing. The Frogeye workshop manual specifies Wellseal. The Mk2 Sprite (Mk1 midget) specifies Hylomar. Likewise I prefer the cork gaskets: trimmed to length.
Alan Anstead

Dave, I think it would be very difficult to see anything useful with an endoscope, as the area concerned is behind the flywheel. But for six quid it's very tempting!

Alan, the new cork seals that just came from Moss were already curved and cut to length. They stood about 5mm high before compression. On dismantling there was no sign of leakage from that area, it was just from the lip seal.

Les
L B Rose

Some interesting comments on leaks from oil pumps and the rear of the engine posted on the Sebring Sprite webpage in Sept 2015 http://www.sebringsprite.com/news2015.html from John Poulter:

"I can’t understand why there should be heavy leaks from around the oil pump cover requiring the cover to be soldered. There is a paper gasket between the pump and block and another around all of the pump and backplate so where would the oil come from unless it’s somehow coming through the back of the pump if it’s a two piece design. I have a 1275 Marina engine where the oil pump cover just rests in a machined groove in the backplate – no gaskets, no seal and no oil leaks on the back of the engine either. I wondered if I was having a senior and grey moment ( I can just do grey at present!) I can understand oil leaking past the scroll and down the flywheel side of the backplate. I have attached a photo of the Payen seal and carrier used on the BMC tractor with 948cc diesel engine for your interest. This was designed and running in 1962. Regards John"
[When I rebuilt my 1098 engine the pump cover was loose and I merely used a smear of instant gasket to seal it. I think John may be right and it shouldn't leak there. I have tried two of the conversion kits to fit a seal on the tail of the crankshaft and despite careful assembly both leaked quite severely. Back to the drawing board. Martin Ingall’s comment.

And

CAN ANYONE HELP SVEN WITH HIS ENGINE OIL LEAKS?
Re: John Poulter's comment - I have stripped my bored 1098 engine (10cc). I think they, as well as 1275s, have the set-up John describes but the eEarly 1098 and 948 engines have a thinner back plate and the cover is soldered on to it from the outside. I was going to convert back to the scroll. However Wolfgang, my local engineer, has increased the radius on the rear of the main cap which usually sits right against the scroll so I cant go back to it. Has anybody got any experience with the MED conversion which is different to the one Peter May is doing in that the seal runs against the area between the scroll area and the crankshaft boss? Does anybody know whether the scroll on 1275s and 2 inch 1098s is the same diameter (54.4 mm on the 1098)? I have a nice powerful engine which is let down by the fact it has a really heavy rear oil leak


Cheers
Mike



M Wood

Thanks Mike

That BMC diesel seal looks a bit better than the Morris Minor Centre one that I have, in that the carrier is not split. The lip seal itself still runs on the crank flange. I've always been slightly doubtful about the split carrier design, as there is no lip round it to keep the seal in. There is only the clamping force from doing up two tiny allen screws - plus sealant of course. Why did they put this on the diesel and not on the petrol engines? Presumably the diesel has the oil pump somewhere else.

Those posts seem to confirm my impression. I have never in 50 years seen leakage from the oil pump area.

This morning I did my usual 5 mile run after reverting to the standard pressure relief valve. Still leaking. I have ordered the endoscope.

Les
L B Rose

I am having a senior moment, as I can't work out whether it's possible to remove the rear main bearing cap with the engine in the car. Is there enough clearance from the backplate? I'm not too fazed by removing the engine again, but the worst problem is getting the steel bonnet off on my own, without chipping the paint. Not within my glamorous assistant's job description.

Les
L B Rose

Pretty sure you need to lose the backplate - but in the past I have taken out the engine with the bonnet in situ. But I was younger and stronger then and had enough humph to simply pull it out. But here's a puzzle for you - its a race 950cc. Where is the oil coming from?

https://www.youtube.com/watch?v=lMfz88lDHW4

If possible it would be better running the engine without the backplate out of the car to determine the source. On my Frogeye I went through every permutation and settled with a Peter May seal kit and 2 1/2" breathers into a catch tank. Nothing collects in there but at least I know the engine can't go above atmospheric or be susceptible to fuel dilation.
f pollock

Well like the commenter on that video I can't imagine how oil can come out of the spigot bush. There must be a passage into the main bearing oil feed.

I enquired about the Peter May kit but it's only for 1275 engines. There seems to be no choice for small bores.

The leak is actually worse now than before the recent work on the crankshaft. Something is seriously wrong.

Les
L B Rose

Les, had you considered trying the rear crank seal modification described in Mascot, I think by Steve Kiel? It involves using a standard face contact seal which works axially with the crank rather than the normal (Peter May) type which contact the sides of the crank on a surface that may not be sufficiently co-centric with the crank for it to maintain a good contact seal. His system is described as being something that can fairly readily be done DIY, is reversible and at very modest cost. Less than £10 for the seal I think it was.

Anyone else tried it?
GuyW

The last time I had to machine an Oilite bush once it was spinning in the lathe a decent sized annular ring of oil formed on the outer surface of the bush and was quickly reabsorbed once the bush had been machined to length and the lathe stopped, I suspect in the video the oil seen is just that held in the bush.
David Billington

Yes Guy I had already seen Steve Keil's solution. Not sure whether to go for that. It requires yet another engine strip down, and making up the tool to dress the bearing cap and upper half. I haven't contacted Steve yet - there is very little detail in the article.

I got the endoscope, but could see hardly anything. It comes with a right angle mirror but that is useless as it's barely shiny. What do you expect for £6? I have the engine out again now. There is a dribble of oil from the bottom of the seal carrier, which I could never have seen with the endoscope. I did wonder if oil was leaking from the gearbox front cover, but (a) I fitted a seal to that previously, (b) oil dripped from the clutch housing while the engine was idling, and (c) the gearbox oil level doesn't go down.

So I am about to get the clutch and flywheel off to see what is going on. Watch this space!

Les
L B Rose

Les,
for future you could put a different colour oil in the gearbox to help distinguish between engine and gearbox leaks.

Or you can put a dye in the oil of one or other to see which it is.

I had to look for this video as proof to myself I wasn't dreaming this and the video is not as I remember it but covers the subject.

228 MG Oil Leak Detrection - https://www.youtube.com/watch?v=6G5IxOCWFE8
Nigel Atkins

I can clearly see the leak now. The sealant I used didn't adhere well to the backplate. I'll redo the whole job with a different sealant. I'll also put Hylomar on the bearing cap mating surface.

The oil dye looks a good idea, but I don't think I need it right now.

Les
L B Rose

Les, when you say "...a new sleeve put on the crank flange, nicely ground now so should be perfect." Do you mean it was ground to be concentric or just ground to a nice finish. If your crank flange was not concentric to begin with putting a sleeve on it won't make it concentric.
Rob
MG Moneypit

Depending on the method used removing a heavy steel bonnet from a Frogeye, prior to engine extraction, was always a 2 or 3 man job.

'billy no mates' therefore made a crane that will remove an engine with the bonnet in situ.

Over the years it has performed well on many Frogeyes.

In the picture the bonnet is off this particular car as it has a front hinged steel bonnet.


Alan Anstead

Nice carpet, Alan!

Seriously, is it practical? Doesn't it get soaked with oil and other fluids?
GuyW

Guy

That is me with the crane but not in my garage. Another advantage of my crane is that it is easily transportable. Its component parts make it easy to store when not in use.
Alan Anstead

Rob, I am struggling to see how the sleeve could not be concentric if it was set up in the lathe or crank grinding machine. It was ground after it was fitted. Anyway, I have checked it with the dial gauge and could not find a trace of eccentricity. The needle doesn't move. That's with the crank in the engine.

My method with the bonnet is to suspend it from the garage roof on ropes, gradually lowering each end bit by bit. Once I have it stood on its rear end I then get underneath and lift it on my shoulders, and stagger across the garage like a tortoise. As the manual says, refitting is the reversal of removal. That is a nice engine crane. I just make do with an RSJ across the garage and a block and tackle I have had for over 40 years. As I have the whole process down to a fine art (engine out in 3 hours) I don't think it's worth buying or making a crane.

I now find it quicker to remove the engine without the gearbox. A lot less to disconnect. I just remove the lower gearbox bolts and loosen the ones in the cockpit. To refit, the trolley jack under the gearbox enables the input shaft to line up. But I'm sure you all know this. This time I could not understand what was stopping the engine from moving forward. I had trapped the speedo cable with the lifting strop! I think it survived, but I'll find out on the road.

All I need now are the new sump gaskets.

Les
L B Rose

My block and tackle just hangs like an ornament these days as I rarely have other makes / models in the garage as the garage is quite narrow.
Alan Anstead

As one gets older, ones block and tackle may well be used less, and hang like a useless ornament.

However, I will draw the line at keeping it in the garage. 🤣
anamnesis

Apologise if I'm stating the obvious, but any surface you want silicone sealant to stick to needs spotless cleaning with something like carbon tetrachloride or cellulose thinners first. Any hint of oil or grease and the adhesion won't work.
f pollock

Les, Re your Endoscope, I just noticed your comment;

" It comes with a right angle mirror but that is useless as it's barely shiny."

I bought a similar one last year. There is a piece of protective film on the mirror that you have to peel off!

HTH

Jim
J Smith

Les, as long as it is concentric to the main bearings it should be perfect. The factory didn't take much care when putting a finish on the flange so whether or not it was concentric to the main bearings was pot luck. This randomness is probably the reason some have no trouble but most have no luck.
It was only when the Maestro 1300 was made that they had to ensure the flange was concentric to the main bearings because they had a conventional seal mounted in the alloy casting used to mate to the VW gearbox.
Rob
MG Moneypit

Looking at the MM conversion, it looks to me like the seal carrier position is determined solely by the 3 tapped threads in the block for the upper scroll. So the assumption is that those 3 tapped threads are perfectly concentric to crank centerline. I don't think this is correct, otherwise a scroll carrier from one engine could be swapped to any another - and this is not the case, any more than you can swap main bearing caps from one engine to another. So what I'm suggesting here is even with a perfectly machined flange the MM seal carrier could force the rear crank seal off centre because the tapped holes were never machined on crank centerline in the first place.
If I'm right it would seem the only way to ensure perfect concentricity would be to allow the assembled seal to find it's own center once the crank is in place and torqued up. That's what happens on the front seal. The deliberately elongated holes allow the front timing cover to self center, and most of us assemble the front timing cover loose so the crankshaft damper can determine the correct seal center before tightening up.
In the same way elongating the holes slightly would allow the carrier to also self center to allow perfect concentricity to the machined crankshaft flange. Just an idea.
f pollock

Yes I cleaned all the surfaces with thinners and panel wipe. And yes the MM kit does allow for seal centring. The holes are elongated and I have been very careful with centring. This time I did not pack the seal with grease, but just oiled the lips. I kept the outside of it perfectly clean and fitted it to the carrier with silicone sealant. I left it overnight to cure and then ran the engine at idle for 10 minutes to check for leaks. A bit of coolant from a loose clip but no oil. Time will of course tell.

Thanks Jim for the tip about the endoscope. I got the plastic film off the mirror (with some difficulty), but it's still useless as the LEDs cause bad reflections.

Les
L B Rose

This thread was discussed between 18/06/2019 and 03/05/2021

MG Midget and Sprite Technical index

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