ok its time to rebuild my 250r. how do i go about picking a piston/rings. should i take the old head off first and measure the internal diameter of the head then go from there or what? what if its in between sizes do i have to get the head bored?

 

best way is to remove the cylinder and piston. measure the piston carefully and order the next size bigger. take the new piston and the cylinder to the machine shop and they will know what to do. good luck .