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MG MGB Technical - Rear main oil leak

I replaced the clutch, pressure plate and throw out bearing on my 67 B about 600 miles ago. The clutch was fine but the throw out bearing had disintergratied and there was no carbon left on it. At the time there was no signs of oil in the bellhousing or on the rear of the flywheel so I did not pull the flywheel and replace the rear main oil seal. I've only done around 600 miles and the engine has developed a massive oil leak from the rear main. It will drip at least a saucer full of oil after a run.

Is there any way the clutch replacement and oil leak can be related?

Thanks

Andy
Andy Preston

If it's any consolation I wouldn't have replaced the oil seal either. This is very bad luck and I certainly can see no link between replacing the clutch and the oil leak. Are you sure the oil is coming fron the engine and not the gearbox. Either way it seems there is not much option but to remove the engine again and replace the offending seal. Just one final thought I don't suppose that the crankcase ventilation hoses are blocked and so raising the crankcase pressure and blowing the oil out past the seal. Might just have nipped one when you had the engine out.
Iain MacKintosh

I wouldn't/didn't replace any of the seals either, or the pilot bearing, working on the principle that if it isn't broke then don't fix it. The more you dig into something the more other things you are likely to upset, quite apart from the iffy quality of parts these days. I was lucky, but I can see that if you were a bit rough parting or joining the engine to the gearbox you could upset either the rear main or front gearbox seals. Incidentally compare the colour of the lost oil to the engine and gearbox oils, usually engine oil is dirtier.

There are two airways into the crankcase - the suction from the inlet manifold or carbs and the filtered/restricted inlet, so you would have to block both of them to get pressurisation.
PaulH Solihull

Ian and Paul thanks for your consolation and reassurance that I probably did the correct thing by not replacing the seal when I pulled the engine and gearbox. The gearbox pulled off the engine nicely and went back together without any force at all. In fact it was the easiest I ever put a gearbox on an engine. The engine was down at least 3 pints of oil and it was black so I guess it's engine oil. My initial guess was pressurization but the PCV valve was clear. Looks like a good job for a rainy day in sunny California. I have 2 other MGs to drive and keep me busy as well as a 55 TF under restoration.

Thanks

Andy
Andy Preston


R&R gearbox/clutch should not affect the rear seal at all. Remote possibility that debris from the TO brg got in the seal, but very remote. I'd check very carefully that leaks from oil pipes, oil passage plugs, rocker cover, etc are not running down the engine and dripping off.
If it is leaking inside the clutch housing, you should be able to see or feel it through the clutch release arm hole, or the starter holes. At that rate, the inside of the housing should be very wet.

FRM
FR Millmore

"At that rate, the inside of the housing should be very wet."

And dripping off the split-pin that should be in the drain hole in the bottom of the bell-housing.
PaulH Solihull

FRM makes a good point. The first time I started the engine in my roadster I had a leak you've guessed it from the rear main bearing. What a disaster. However on checking further what was happening was that a trickle of oil was running from the rear side cover down the front of the backplate and off the splitpin. The oil was so clean that it was impossible to see it. After sorting out the sidecover no more problems.
Iain MacKintosh

Andy don't feel too bad the professionals don't always get it right. My wife's 2010 mercedes had the gearbox out twice to fix an oil leak from the bell housing . Rear main seal etc., before mercedes found that the oil was cumming up a head bolt and running into the top of the bell housing and out the bottom. Three weeks off the road. F.M. has a point Sean
S Sherry

I had the car on the lift and dark oil is dripping from the hole at the bottom of the bellhousing and from the clutch release arm. FRM had a good idea to remove the boot around the clutch lever and see if I can see anything. Thanks for you consolidations.

Andy
Andy Preston

Sorry! Any idea how old the seal is/was?

FRM
FR Millmore

Oh dear, looks like you have a job on your hands but make sure to fit the uprated seal as fitted to the Sherpa van.
Iain MacKintosh

Does your engine have an inspection cover on the front-right side of the rear plate? (rubber cover)....
If so, pull the cover and feel the front side of the fly wheel, and the back side of the plate....If it is really oily, than it is your rear seal....If it is dry, than it could be an external leak, or the front seal on the tranny...
I found mine, by using UV dye....(available at auto parts, ), and a UV lamp....
Put the dye in the motor oil only...If the drip shows up bright lime green, then the leak is from the motor....
If the drip shows up dull blue or not at all, than it is the tranny oil....
It will also show up motor oil coming from other areas of the motor.
If it turns out to be the rear main seal, use the Graaco seal, and a Speedi-Sleeve, and you will stop the leak...
I have photos of the install, if you need them.
(email for pix).
Edward
E.B. Wesson

FRM the engine has never been apart even though I have removed it on several occasions to rebuild the gearbox and then install an O/D and recently to replace the clutch. The engine has 70,000 miles on it from new.

Andy
Andy Preston

This thread was discussed between 19/09/2011 and 24/09/2011

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