[AZKen]

If I'm reading Barry correctly, he is saying a piston can be oversized out of the box by .001 and standard tolerance for a bore allows it to be undersized by .0015, A big piston in a small hole would have a .0025 build up of tolerance. The recommended skirt to bore clearance is .0027-.0033. (305 V6) So that seems like what he is saying can happen to "eat" up all the tolerance if the actual as machined and as purchased mating pair is not measured and matched to create the required skirt to bore clearance. Also wrong ring gap can play a roll in friction heat, I think. IMO, You always buy your pistons first and take them to the machine shop before boring. It is very cool that GMC used aluminum pistons way back, very leading edge for the period.