I completely stripped the bike down to the frame getting rid of all that rust...i got the motor on my bench with the head and jugs off its original bore not ovalized 64 all around no marks on the wall the rings were not seized pistons are like new(original pistons) since i have the gasket and seal kit im this far just as well to do it now and save future problems.......and what would be the best oil to mix i always liked klotz in my skidoos but my parts dealer told me to use castor 927 it was suppose to be better??