What Are the Different Types of Piston Rings?

Three or four piston rings are most commonly used and located toward the top of the piston

The internal combustion engine has been in use for over a century, and though it has been modified with the advancement of modern technology, it is still constructed using the same general parts and configurations.The piston rings are among the most important internal engine parts.

Types

There are only two types of piston rings: compression and oil. A typical combustion engine will either have two or three compression rings. These rings are always the top rings of the piston. The oil ring is located under the compression rings, and only one oil ring is used. These rings are most commonly made from iron, but are also available in steel or chromium plate.

Function

Properly working piston rings offer efficiency and protection for an engine. The compression rings provide a tight pressure seal to ensure maximum energy and power efficiency from the engine, while oil provided by the oil ring lubricates and protects one of the most vital components of the combustion engine: the piston.

Shape

Piston rings follow the generally circular shape of the piston it fits. Beyond this circular shape, the profile can be a number of various shapes to fit any number of requirements. Rectangular is the most common and basic profile used, but the outside edge can also be rounded, slanted or have a combination of edges.

Size

Piston rings are made to fit every diameter piston used in every combustion engine from those used in small lawnmower engines to those used in large truck and marine engines. These diameters can range anywhere from a fraction of an inch to over a foot.

Longevity

Piston rings are made from iron or steel and are built to last. Under proper engine maintenance (mainly oil changes), these rings can last as long as 150,000 miles or more. Engine power modifications can alter the temperature and pressure of the combustion chamber, thus creating a more extreme environment that can wear rings down rapidly.

References

• Engine Builder's Handbook; Tom Monroe; 1996
• Engines: An Introduction; John L. Lumley; 1999