Metal rings located in grooves near the top of the piston. The rings facilitate high compression and keep oil from leaking into the combustion chamber. Usually 3 rings on each piston.

As the piston moves up and down inside the cylinder, the rings ride smoothly on the cylinder walls. Depending on the position of the ring, it’s function is to keep compression in the cylinder or scrape oil from the cylinder wall so as not to be burned when the piston / cylinder fires.

As a rule of thumb, the top piston ring is the compression ring #1, the middle ring is the compression ring #2 and the bottom ring is the oil ring.

If either compression ring fails, this will cause low compression in that cylinder and cause an engine misfire, possible check engine light and engine noise as well. If an oil ring fails, you  may see blue smoke from the exhaust and engine misfire as well.

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