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Measureing piston/bore clearance?

polkat

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When measureing big block piston to bore clearance using the stock aluminum pistons, where on the piston should the measurement be made? I've heard that the feeler gauge method is inaccurate, and that a true micrometer should be used on the skirts, but, as the piston is not concentric when cold (more of an oval-and somewhat smaller at the top) where specifically on the skirt should the measurement be made? I'm thinking 90 degrees to the pin, at pin height. Yes? Thanks!
 
It's kinda barrel shaped and it's shaped like that even when it's cold. One way to find out if it grows and how much is to heat it up in an oven then mic it but I always measure cold. The clearance figures are for a cold piston. Anyways, I measure in a few places starting just below the oil ring and end up at the bottom of the skirt. This also tells me if the skirt is as it's supposed to be. The piston is usually about .010 smaller around the ring lands. The feeler gauge method isn't dead on but it's a good way to see about where you are. Btw, stock factory piston to bore is pretty tight....
 
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