Re: engine rebuild

Posted by Marco on Oct. 19, 1998 at 22:33:25

In Reply to: engine rebuild
posted by Jim Sims on Oct. 19, 1998 at 20:43:29

Jim,
I suggest getting an probable estimate from your machinist on where the bores will clean up. Technically the bores should be actual measurements i.e., .040" over would be 3.915". However the finished size should be to the individual pistons. While the quality and consistancy of pistons has improved in recent years, you won't know until each piston of the set has been measured. A decent machinest with the proper equipment will match each cylinder to a piston within .00005". It may seem like over kill but costs no more to do it right. You don't want to pay for the setup twice.
The flywheel housing should be checked around the rear flange to be true within .006". This was originally done with special tools but equivilent to using a dial indicator attached to a mag base on the rear crankshaft flange. As you turn the crankshaft the dial indicator rides on the housing flange and measures the variation. We don't usually have the option of throwing out the housing and replacing it with a new one as done originally. Some creative shimming (and several hours of trial and error) will usually get it there. The shims were the same thickness as the gasket so that is usually your best starting point. After installation of the flywheel, it should be similarly checked for eccentricity and wobble by positioning the mag base on the housing and having the indicator ride against the flywheel. The limit on both eccentricity and wobble is .005". Be sure there are no burrs between the crankshaft and flywheel. You will also find that the flywheel will run closer to spec installed in one of the two possible positions.
If the number boss on the block is smooth or has signs of grind marks then the number has been removed. If the boss has a cast texture similar to the surrounding area, then it is likely it was never numbered. This would indicate a bare block or otherwise incomplete engine made available through service. There were some casting differences on "A" blocks manufactured in the late 30's, but I'm not familiar enough to describe them.

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