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MG MGA - Rear bearing oil leak

This question is about my MGB, but is most relevant on the MGA forum.

I have installed a Ford type 9 five-speed gearbox in my 1963 MGB, which has the original 3 main engine. This is a complete success, but may have an unexpected negative side effect: It seems to me that more oil is now leaking through the rear main bearing.

Like the MGA, the 3 main MGB engine does not have a proper oil seal at the rear bearing, but a scroll seal that is supposed to bring the oil back into the engine through rotation of the threads. And as you all know, some oil is always leaking through here.

If it is really leaking more oil now, I have a theory.

My engine is bored +.060, has a Peter Burgess Econotune cylinder head, but is otherwise standard. This means that there is a lot of low down torque, and I really enjoy that with the new gearbox. I now often find myself cruising at less than 2000 rpm.

Can it be that this creates an unfortunate combination of crankcase pressure and lower efficiency of the scroll seal, because the rpm are lower? Or is there any other explanation for what I believe is an increased oil leakage?


Crankcase pressure is most likely. Is your draft tube working OK?
Art Pearse

No, its not. I have used a small air filter on the valve cover to hopefully let some pressure out, but I guess oil may have clogged it. I will have to get a proper tube to the front air cleaner as original.



I had the identical problem on my ZB Magnette fitted with the early MGB 3-main (also +.060). My solution was to use the Smiths PCV. See my article:


Andrew Dear

Andrew, I'm interested to see how you solved the oil leakage using a Smiths PCV. However, I was unable to open your link, it is telling me that I am forbidden to open it.

Thanks Frank
F Camilleri


The link works OK for me.
Is it your computer setup?
Some sites may be blocked by your browser settings.

M F Anderson

Link also worked for me - I have this setup on my MGA roadster - 3 brg MGB engine - works fine, no oil leaks - the simplist pcv system.
Mike Ellsmore


Thanks a lot for your article. Seems that is the way to go!


This thread was discussed between 16/05/2014 and 18/05/2014

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