I have read on this site to measure the piston diameter 10-15 mm up from the bottom of the skirt, but not have any tool accurate enough to measure piston or cylinder. So i put the piston in the bore and slipped feeler guages between. This with piston at TDC. Measuring from the top down, clearances were loose at the top and tighter at the bottom. Is there a certain method to use?

Is this because there is more heat and therefore more expansion at the top of the piston as that's where all the heat is?

And if you measure a piston 10-15mm above the skirt, this implies the piston is not truly a cylinder with constant diameter? If it were, you should be able to measure diameter anywhere. So is the piston tapered and the bore straight?
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