Btw I have built hundreds of motors, and installed pistons from most manufacturers (wiseco, J&E, mahle, Kieth black, etc.) I would never in a million years assume that .010" rings will not have tight gaps and install them into a .010" bore without checking. It is easy to do and I have seen the results of tight rings on a motor. That motor ( built by a new mechanic) ran fine until it was broken in, but it's first trip on the freeway (first time it attained that high of a temperature) it siezed in the bore and galled the cylinder. The mechanic was shocked that you have to check the ring endgap! He said " it's said on the box it was standard!"
To check end gap you place the ring in the bore. Using either the piston, or a ring squaring tool you square the ring (make sure it is perpendicular to the bore) Then you use a feeler gauge to determine the gap. If it is not at least .004" per inch of bore you MUST file it to attain this clearance. Equally important is the piston to cylinder clearance. The optimum means of checking this is with a dial bore gauge and a micrometer. A quick and dirty way is with long feeler gauges. The clearance will vary with the material ( forged,hyperuectic,cast, etc.)The intended usage ( low rpm street, high rpm racing, etc.) And the thermal range expected. Typically a tighter clearance will be less oil consumptive, quieter, and longer lasting, when used within it's rpm and heat range. The trade off with looser pistons is noise and oil consumption for the ability to survive higher temps ( racing?) and more abuse. As an aside the reason forged pistons need more clearance is that they are denser, and therefore expand more when heated. Also the construcion (design) affects clearances. The more material in the piston crown, the more it will expand. If you could look at a pistons profile you would see that it is substantially smaller in diameter at its crown than it is at it's skirt. This is because of the amount of material, and it's coefficient of expansion. Bottom line, check everything while your motor is being built, instead of wondering if you should have when it is not running right after it is assembled!
