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MG MGA - Gearbox Query

Just rebuilding straight gearbox for my race car, and have changed front cover and fork to 'B' type.
Some of the gearboxes I have stripped have shims between the cover and the front bearing.
In my (factory) workshop manual it does not say how to shim this up.
Does anyone have any ideas?

Colin
Colin Parkinson

You need to use a depth micrometer to measure very carefully the depth of the pocket in the front cover and the protrusion of the bearing ahead of the case. Also measure thickness of the paper gasket. Add pocket plus paper and subtract bearing to find the space remaining.

Install shims to occupy as much space as possible without making interference. After shimming remaining space should be 0.000 to 0.003 inch. When in doubt, leave a little more space, because if you have interference fit the gasket will leak.
Barney Gaylord

The basic procedure was well described above by Barney. One more optional step: for insurance, I like to do a trial fit (or two...) with a small strip of plastigage to physically check how much space is left. Plastigage is a cheap soft plastic strip that will get wider as it gets compressed and give you a reading of the space left. Available in most automotive shops.

Karl
Karl Leclerc

Well I have had a look today and I have a problem!!

If I get the front bearing so it is flush to the case the rear sits out about 40 thou.

I have torn the box down again, twice in fact, and can see nothing wrong, but the tailhousing will not go flush!!

So will have to have a look at the rear bearing tomorrow. Maybe it is not on the mainshaft correctly?

I will probably strip the whole mainshaft down, and do a trial fit with the first motion shaft and the main shaft. See what that looks like.

CP
Colin Parkinson

This thread was discussed between 13/03/2006 and 14/03/2006

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