How are compression rings lubricated?

Question

My question relates to the lubrication of cylinder walls and piston rings. It is my understanding that pistons in cars consists of 3 rings; two compression rings and the oil/scraper ring.

As far as I've read, the cylinder walls are only lubricated by the jet of oil coming out of the connecting rod holes, and any excess oil is primarily scraped off the walls by the oil ring (consisting of 2 small rings and a center bent shape ring - correct?)

If I'm correct on this, it seems intuitive to me that oil would never reach the compression rings as it is scraped by the oil ring sitting beneath it.

How is the compression ring then lubricated and kept from scoring the walls?

Solar Mike · Answer

The answer is that the scraper ring does not remove 100% of the oil, a VERY thin film is left on the surface which provides the lubrication necessary.

Some engines will score the walls, but others, on re-build need "glaze-busting" to remove the baked on layer of oil deposited over time.

alex hazeltine · Answer

there are several ways that rings are lubricated for example in a two stroke its done by means of petrol /oil mix in certain 4 stroke engines you will find a jet which sprays oil onto the bore and skirt of piston and as stated the oil scraper rings do not remove all oil also the cross hatch in the cyl holds a degree of oil which provides some lubrication

Answered by alex hazeltine on August 26, 2021

How are compression rings lubricated?

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