I had a ring break off on the PTO side of my 670 and was flying around inside for awhile I would guess. The inside of the head is just battered. Does anyone know if a machine shop could machine down the combustion chambers and then plane the head to bring the compresion back down to normal??? I have already bought a used head so we can ride this weekend, I was wondering if I could use this for a spare in the future if the need arises. My 670 is now a 677!