I have to bore out my cylinders and I'm having trouble figuring out what the STD size is for the cylinders! My current piston tops show 6 82

Its odd because they typical go 6 25 or 6 50 or 6 75 if there Over sized by .25 .50 .75

I want to go .50 OS BUT idk if they're already .82 OS but that makes no sense to me and to get a custom made piston and rings would be way to much for this lil bike so i doubt anyone did that.

Any help mates?

Yip mike, go Wiseco , they make pistons up to 2.00 over size, lots in USA, have a browse and see,

Forged pistons and are very hard waring

Look - in USA, 60.96

http://www.ebay.co.uk/itm/NOS-Yamaha-YR1-60-96mm-pistons-2-/111213147190?pt=Motorcycles_Parts_Accessories&hash=item19e4d1f436

wiseco is the way..great pistons