[rotorwrench]

The center main tends to wear faster than the others. If it had a good bit of wear then de-shimming can set up a pressure on the center main that is trying to pull the crankshaft off center a bit. This is a possibility as to why it turns tighter than it should.

Different pistons sometimes required more clearance as was mentioned previously. Manufacturers of the pistons usually have recommended clearance for their product. Forged pistons require more clearance that plain cast pistons. Split skirt pistons may get away with less but I don't know how many or if any pistons are available with split skirt design in this day and age. They are somewhat weak due to the split.

If the crank is ground, the babbitt will have to be replaced.