[Tom Endy]

The shims at the top of the flywheel housing in the two ears is what aligns the top 180 degrees of the housing. The bell housing will pull the bottom 180 degrees into alignment. The shims are horse-shoe shape and are .010 thick. Sometimes a housing that is whacked out of shape slightly can be pulled into alignment by adding or subtracting thickness at one or more shim.

My experience has been that the thickness of the lower gasket is also a factor. Gaskets from suppliers are all over the map, most too thin. The reason for the .010 shims is to equal the thickness of the lower gasket when crushed down. Therefore the gasket should be around .010 - .018 thick. I purchase gasket material from Napa of the proper thickness and cut my own.

Sometimes a flywheel housing is so whacked out of shape you cannot align it and it should be discarded for a better one.

I have a theory of how they get whacked out of shape. People changing a timing gear jack up the front of the engine in order to get the timing cover off. If there are solid rear motor mounts, something has to give, the flywheel housing. Best to loosen the rear motor mount bolts when changing a timing gear, not always practical along side the road. Most flywheel housings are found with cracks at the lower two mounting holes.

The late 31 flywheel housings have support ribs at the bottom section of the housing to better protect it from being whacked. Sometimes they show up at swap meets. That is how I found mine.

Tom Endy