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MG MGB Technical - Rear 3 Beaing 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 MGA or MGBs. 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 3 bearing engine was rebuilt in December 2013. Initially it didn't leak oil at all. It has certainly been 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 me removing/refitting the sump? Any other possible causes? Any other comments?

In all other respects the engine is running beautifully. Compression fine at least when cold. Another point is that I think it gets exponentially worse as revs go up which is perhaps not surprising. It is fitted the early oil breather set up, i.e. it is the early type with the valve but this has been done earlier this year, i.e after the problem showed itself.

By the way the car is actually an MGA with this early MGB engine hence the question on this list.

Paul
Paul Dean

I assume the oil is diminishing in the sump by the amount you are losing? Oil can also come from the gearbox into the bell housing.
If the crankcase is being pressurised this will have the effect of easily defeating the rear scroll. Try by-passing the breather system altogether and see if the problem still persists.
Allan Reeling

How early? If it doesn't have the PCV valve on the inlet manifold, just the hose from the from the rocker cover to the front air cleaner can, and the other hose hanging down from the front tappet chest cover, you can check the ventilation system by making sure you can blow air through one of the hoses and it comes out of the other i.e. doesn't pressurise. Both hoses would have to be blocked, or sealed off, for the crankcase to pressurise

If it has the PCV valve then that should be putting the crankcase under slight negative pressure, with a ventilated and restricted oil filler cap letting a limited amount of filtered air in. With this system if you remove the oil filler cap on an idling engine the idle speed should change slightly. If you then lay a sheet of paper over the oil filler it should be sucked down onto it. However try it with the palm of your hand first, if the PCV is faulty it can apply a much stronger vacuum which could suck a sheet of paper in. If you have this slight vaccum, and it is the sump oil level that is reducing, then as far as I'm aware it can only be the rear main seal significantly worn.

If you have the early system without the PCV, then fitting a PCV and ventilated oil filler cap may well reduce the oil loss.
Paul Hunt

You may not have properly installed and sealed the rear cork seal at the back of the oil pan when you removed and replaced it. This would explain the sudden loss of oil. RAY
rjm RAY

Suspecting as Ray said I re-did the sump core seals in the summer. A question Ray and others if the cork seal is not working properly can this cause oil to get into the bell housing? (Or just out the outside of the sump.)

Paul
Paul Dean

Paul H, OP said it has a valve which I read as a PCV.

Paul D, sump gasket would not cause oil to get in to the bell housing. Use Paul H's suggestions to check if your PCV is working correctly. After that you need to decide if it's a worn scroll seal or excessive blow-by caused by sticky rings.
Please explain further the comment "Compression fine at least when cold. Another point is that I think it gets exponentially worse as revs go up which is perhaps not surprising." Compression should be the same irrispective of speed (assuming you head can breath well right up the rev range).


Best of...
MGmike
M McAndrew

Based on all the helpful comments 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

As rjm said, the rear cork seal. Check closely that the oil isn't actually running down the rear engine plate and around to the cotter pin.

Herb
H J Adler

As I remember the rear bearing cap is installed with sealant to the mating surfaces. It's absence would allow oil into the bell housing. BUT is the oil caught in your drip tray equal to the amonunt down in the sump?
Allan Reeling

Fair enough that disabling PCV didn't make any difference, but have you confirmed that the PCV was functioning correctly when it was fitted?

If sump loss is greater than what you are catching, bear in mind that the engine could be losing from other places as well.

I'm gradually working through my oil leaks, top down then front back. It makes the occasional drip while parked, minimal loss, but after a couple of hundred miles in torrential rain a few weeks ago it didn't start dripping for about three days :o)
Paul Hunt

Answers to above.
1) there is definitely no oil come down back-plate or sump where cork seal is, so no problem there.

2) My oil consumption is certainly higher than what I am collecting. I am probably using around a pint every 200 miles which clearly is high but in that mileage I collect around 100 to 150 ml, i.e. around 20 to 30% of what I put in hence so some is going elsewhere. I know that more oil comes out of the bell housing than I collect. Some coming out of the cotter pin and running along the bottom of the gearbox and some coming out of the clutch rod seal. Obviously some will be going the other places B series oil goes. There is no evidence of significant oil burn.

3) When I took the PCV assembly off there was significant oil in the tappet cover but I could blow through it. The valve itself was new this summer, how would you test it? But clearly it isn't part of the picture at the moment as I have gone back to the simple down pipe.

Paul
Paul Dean

"how would you test it?"

As mentioned earlier:

"If it has the PCV valve then that should be putting the crankcase under slight negative pressure, with a ventilated and restricted oil filler cap letting a limited amount of filtered air in. With this system if you remove the oil filler cap on an idling engine the idle speed should change slightly. If you then lay a sheet of paper over the oil filler it should be sucked down onto it. However try it with the palm of your hand first, if the PCV is faulty it can apply a much stronger vacuum which could suck a sheet of paper in."
Paul Hunt

Thanks Paul H. Over the winter I will reinstall the PCV,as removing it hasn't helped,then I will test it.

Paul D
Paul Dean

This thread was discussed between 04/10/2015 and 12/10/2015

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