how to determine/buy the right ring size?

[breakdirt916]

If you get some new piston rings, and they don't fit, how are you supposed to determine what the right size is and get the right rings?

should I just walk into a shop with the piston and old rings and say "got any of these"?

the measurements of the piston and cylinder match up to what a stock bore should be...so after honing the cylinder, I ordered some stock rings from the honda dealership, but they don't fit: the top two rings are too thick to slip into the cylinder and the lower crown-looking copper ring is also too thick

how else could I go about figuring this out to get the right size ring?

[Kurlon]

I'm guessing that the compression and scraper ring need to be gapped. The oil ring will fit, someone will just need to show you the right technique for installing and then sliding into the cylinder.

[SSearchVT]

Does the piston fit the cylinder? On the top of the piston there's a number stamped in if it's oversized.

Depending on what you're working on - the rings may need to have the end gap adjusted. Utility ATV's and light duty 4 strokes - just run them as they come out of the box. High revving dirt bikes that don't get torn apart routinely - dry fit the rings in the cylinder, check te gap, and adjust as needed. If you're careful you can do theis with a small hand file, or a disk on a dremel tool. Otherwise there are specialty tools that make it a snap.