i just received my new piston and rings today to freshen up my honda 250r. problem!
compression is at 85 psi. everything looks good except there is a 1/4 inch gap between the top of the piston and the cylinder. i run a spacer on my pro-x cylinder
which is about the same size as the gap. do you think they sent me the wrong piston.
i sent my old piston with my cylinder when i had it bored so i do not have it. my question is should the piaton go to the top of the cylinder? i want to ride this weekend, so please respond. i may try to remove the cylinder spacer and see if that helps. airtime

I'm not sure on the 310 kit but there is 2 diffrent 250R pistons, A long rod & a short rod piston. It sounds like you have a long rod piston on a short rod.
Look at your old piston & measure the pin highth & compaire it to your new piston.
I got a short rod piston on my old 250R that had a long rod & it stuck out the top about 1/4 inch.

moose,
i would like to measure the old piston but i sent it to tmm so they would send me the right piston back. i think you are right. i hope removing the cylinder spacer puts me back in business. airtime

Make sure you check all of your clearances before you crank it!

thanks, i will. airtime