The piston ring is a thin, circular piece of flat metal that is wrapped around the pistons of an internal combustion engine. There are two major types of piston ring: sealant and cleansing. The sealant ring is used to keep engine gases from blowing into the crankcase which will lead to nasty things being put into the oil and a loss of engine compression. The cleansing rings are used to keep the lubrication evenly distributed on the cylinder walls as the piston completes its stroke. Piston rings are usually cut on one side like the letter 'C' and then compressed on to the piston which is then fitted into the cylinder. Some are completely circular and need to be "stretched" over the piston head. Due to the high pressures on one face and large amount of heat and friction on the other, piston rings are made of strong metals such as chrome-moly. The piston ring is an integral part of the internal combustion engine.

Pis"ton ring. (Mach.)

A spring packing ring, or any of several such rings, for a piston.


© Webster 1913

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