Hello, You can still have Ring issues with good compression. The pistons have different types of rings on them to do different jobs. The top rings are your power rings, the bottom rings are your oil rings.
The oil rings prevent the block pressure and oil slop from being drawn up into the cylinder. The piston creates a siphon action and the oil rings prevent the oil from climbing the cylinder walls. All it takes is for the rings to rotate around the piston and have the ring ends line up.
That is why you offset the rings on installation from 90 to 120 degrees. It staggers the gaps of the rings for a better seal. Now you can get oil vapor if the compression rings line up to allow compression into the crankcase through the gaps on the piston rings.
Sometimes the valve stem seals can leak and allow exhaust into the upper block if you have valves that are not seating correctly.
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