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MG MGA - Rear Engine Leak.

My engine currently looses a significant amount of oil into the bell housing which very occasionally causes clutch slip. I have a collecting tin under the cotter pin and I am catching from 50 to 80 ml per 100 miles. I was also loosing oil via the starter Bendix hole but this is now stopped by fitting the Bendix cover that was fitted to other B series of the day but never to MGAs. Some oil was also coming down the clutch rod but I have almost eliminated this by putting a cable tie around the new but not tight repro seal.

The engine, MGB 3 bearing hence similar to all MGA engines in this respect, was rebuilt in December 2013. Initially it didn't leak oil at all. It has certainly been doing loosing it all this summer and possibly at the end of summer 2014. Clearly a way excessive oil can get into the bell housing is if the crankshaft scroll/housing is worn but I can't understand how this can happen fairly suddenly. The other point is that some time later in last summer I did remove/refit the sump and it is possible this problem started after this, can't be sure though.

I suppose my main question is this, is there any other way engine oil can get into the bell housing except through the scroll? Could it have been caused by my removing/refitting the sump? Any other possible causes? Any other comments?

In all other respects the engine is running beautifully. Also I have fitted the MGB oil breather set up, it is the early type with the valve but this has been done earlier this year, i.e after the problem showed itself.

Paul


Paul Dean

Paul, I had a somewhat similar problem with an MGB 3-main engine I fitted to my ZB Magnette a few years ago. It was a newly remanufactured engine and it blew all its oil out of both the draft tube and the crankshaft scroll on a single trip from Menstrie to Nairn and back. Naturally, being a newly rebuilt engine it went back to the builders!

As I understand it the solution in my case was to line bore the main bearings, which I presume restored the proper clearance on the scroll. I also did as you have done and fitted the MGB breather system to replace the draft tube.

In your case, with the problem apparently starting after a long? period of satisfactory running, I think I would want to carry out some compresssion testing and a blowdown test to see whether your engine could have developed an excessive leakage of combustion gasses into the crankcase - broken rings perhaps?. It would need to be bad though, if the modified breather system is unable to cope. Did you fit the Smith valve or use the carburettor connections? I had to use the Smith valve as I am still using the Magnette's original H4 carbs.
Andrew Dear

Thanks Andrew. I have checked the compression on a cold engine and all seems fine but I will check again on a warm engine. Like You I use the Smith's Valve.
Another point is that I think it gets exponentially worse as revs go up which is perhaps not surprising.

Paul
Paul Dean

I do lose some oil from my 3-bearing MGB engine in my MGA too but it isnt really excessive, after the last 2600 miles it needed about a pint and a half.

Im fairly certain that most of this has dripped out of the rear bearing scroll and has not been burnt in the engine.

I have no vent at all in the alloy valve cover of my engine and so maybe there could be some pressure building up in the crankcase.

I am however in the process of fitting a vent in the cover so hopefully this will help.

But if your car is an example of how effective the fitting of a PCV valve really is, then maybe not. :-)

Colyn
c firth

Colin - I have never heard of oil consumption as low as yours on a 3 bearing B series engine. I don't think my comments on breathers should put you off though as my issue is something a lot more than this.

ALL - I still welcome comments on my core questions.

Paul
Paul Dean

Rear engine leak? That's strange, my engine's in the front! Sorry!
Lindsay Sampford

Paul, I just checked the oil container I had in the car and it was bigger than I thought.
So I actually used 2.5 pints of oil in total, sorry about that.

Colyn
c firth

We can all see where you have been Colyn!
Lindsay Sampford

Is that a Sherlock/sleuth type comment Lindsay?

What I "presume" you mean is that you can all see we we have been by following all of the thousands of drips of oil my car has left on the road?
:-)

c firth

Paul,

Maybe you should check that the engine side plate is allowing a free flow of gasses out of the crankcase. The metal gauze packing can get gunged up which will defeat the suction from the Smith valve.

You might also check whether you can detect any gas blowing out of the rocker cover vent. When my engine was losing oil badly it would cause a piece of paper to float if I held it over the open vent! See photo. If the positive crankcase ventilation system is working correctly there should be a gas flow, but in the opposite direction!

Andy


Andrew Dear

Colyn, there must now be a trail of oil all the way from Lands End to John O'Groats! I don't think your car drops as much oil as mine does. I've got friends who tell me not to visit them in the 'A'!
Lindsay Sampford

Back to the original point and Andrew's input in particular.
Based on all the helpful comments here, and also on the MGB Technical board, I have now done the following:-

1) Removed the valve type breathing system and put it back to the simple down pipe system (with earlier tappet cover carefully sealed) as used on all MGAs and the earliest 3 bearing MGBs. After a relatively hilly 70 mile motorway run (Forth Bridge to Perth and back) at between 4000 and 4500 rpm this change appears to have made no difference around 55 ml collected in my catcher below the bell housing cotter pin. There was also some oil still finding it way out along the clutch activator rod. I presume this means this issue is nothing to do with engine breathing systems.

2) I have also done a full compression test on a warm engine and all cylinders are between 160 and 165. Sounds OK to me?

Are there any other explanations except that some way the scroll has been damaged?

Thanks for all the comments.

Paul


Paul Dean

I think that you have proved that is isnt excess crankcase pressure causing the oil to leak out of the scroll.

An open 1/2" pipe in the tappet side cover and another in the rocker cover vented to the carbs would surely prevent any pressure build up?

I have heard that a perfectly engineered scroll can work well at first but soon begin to leak after a few thousand miles.

I suppose it depends how much the leak bothers you Paul.

Do you put up with it until the next engine rebuild?

Then do you replace the entire scroll assembly and hope for the best?

Or do you go the expensive re-engineered back plate route with its fitted oil seal?

Colyn
c firth

Colyn says: "Or do you go the expensive re-engineered back plate route with its fitted oil seal?

For my money, Yes, when you next have the motor out! And it is not that expensive.

Barry.
Barry Gannon

Yes I agree just manage it for now and do the oil seal mod at some time in future.

Thanks.

Paul
Paul Dean

This thread was discussed between 03/10/2015 and 10/10/2015

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