i have a 94 vmax 500 yamaha snowmobile.i have 117 compression on one side and 25 on the other side. i have taken my head off and the piston with compression looks like it has been working(blackish color on piston and head).now on the side that has low compression the piston and head look shiny but piston is pitted around the edges a bit but not to bad. my question is do i replace the rings alone or replace piston as well.