S
Need some advice. Rebuilt my son's twin cylinder 340 Cat (2500 miles) twice now. First time it had lost compression but (surprisingly) did absolutely no damage to cylinder walls or pistons so just replace rings and honed x pattern on walls as done many times before on machines. He got 300 miles and compression went to 60 and 90 PSI but again absolutely (from looks) no damage - not a scuff or scratch. Checked ring gap (.045) and cylinder to piston clearance (.003). On first rebuild the rings were worn a lot and sticky so could imagine reduced compression but this time rings were nice and loose and not worn with good spring. Could it be a bad break in the second rebuild?? Any hints appreciated. Happened at 30 -40 below but we run in that all the time. Thanks for any help. Stan from Tanana, Alaska