Finally got piston for my 1985 yz250 took cylinder to machine shop it measured 68.34 mom standard is 68mm so ordered standard wiseco piston piston was boocoo easy to install but had massive trouble getting cylinder over it finally was able to get piston to go in where I could bolt cylinder down snugly I hand cranked the kicker and the piston got stuck at top of stroke I tried taking off cylinder but at top of stroke cylinder wouldn't go over bolt I ended up smack I g piston down with my rubber mallet I took off piston tried putting it through cylinder on the floor it kept getting stuck 7/8 to top of cylinder