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

 

might try the honda forum.......

 

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

 

ive just found no matter what the bike that the yamaha forum is the most helpful

 

Can't you just measure the piston with a caliper???



all I know.......from my math........is that volume of a cylinder is (pi)(r^2)(h)


Where r would be your radius(bore), and h is your height(stoke)

 

I believe its a 74.5mm bore that would make a stock cylinder stock bore machine a 310. Not sure what kind of setup your buddy has, but if he's replacing rings and piston he should hone out then measure the cylinder to get the right size. Most of the pistons in that size are availible in half mm increments.

 

but hes got a +2 stroker also/...

 

a 73mm piston with a 2mm stroke would make it a 309.7cc engine.

 

u guess that would be what they referto as a 310?

 

Pull the head, clean the top of the piston and look. They are marked usually with the size.