Piston diameter measuring help needed

[yalipito]

I took my intek apart and if I measure the piston at the bottom of the skirt it measures 68.2mm but between the two upper rings it measures 67.8mm. Where is the proper location to measure? Thanks

 

[KustomKartKid]

In general....90 degrees from the center of the wrist pin bore.

In boring and honing operations, several measurements are taken and averaged to calculate clearance.

 

[ole4]

90 degrees to the wristpin as kustom kart said and about 3/8th of a inch from the bottom of the skirt. Pistons are ground with more clearance near the top to account for heat expansion. While I like to mike the piston and use a dial bore gauge to check bore a long feeler gauge works well to see if you are in the ballpark.