Originally posted by pro60chevy
It's pretty tough to measure piston to wall clearance using a feeler gauge with the pistons in the bore. The proper way to measure it is with the piston out. The clearance is usually .001 for every 1" of cylinder bore, on a stock rebuild.
To clarify what Pro60 said, best way to measure is with micrometers. Measure the piston with an outside mike and the cylinder with an inside mike then subtract to find the difference and divide it by 2.

Pat