Ok here the problem my friends has a 250r with a hotrod stroker crank that is +2mm and its a 310 well its wore out and he needs new rings and we dont know how to tell how many MM the piston is to get rings for it can anyone help us

 

its more of a equation than simply knowing the stock bore and stroke of an 88 R is 66X72 and that makes it a 248
and i got it in the honda forum too