Types of Piston Rings and What They Do: Compression Rings vs. Oil Rings

What is a piston ring?

A piston ring is a metal ring that sits in a groove around the piston. It is the part responsible for sealing inside the engine: it keeps the combustion chamber gas-tight, controls how much oil stays on the cylinder wall, and carries heat from the piston crown to the cylinder to cool it. These small rings have a direct effect on an engine's power, oil consumption and lifespan.

The three types of piston ring

Most engines use three rings per piston, from top to bottom:

• Top compression ring — takes the full heat and pressure of combustion and seals the burning gases so power is not lost.
• Second compression / scraper ring — backs up the seal and scrapes excess oil off the cylinder wall.
• Oil control ring — meters the oil on the cylinder wall so lubrication is enough but the engine does not burn oil.

The three core jobs

1. Sealing — keeps high-pressure combustion gas above the piston, maintaining compression and power.
2. Oil control — leaves the right oil film on the cylinder wall and keeps oil out of the combustion chamber.
3. Heat transfer — moves heat from the piston crown to the cylinder wall to prevent overheating.

Common materials and coatings

Piston rings are typically made from cast iron, steel or ductile iron, and their faces are often chrome-plated or nitrided to improve wear and corrosion resistance.

C.T.I. (泰茂實業) has specialized in piston rings since 1973. Our compression rings, oil rings, valves and engine overhaul kits are exported to 110 countries and cover a wide range of makes and engine models. For selection help, OEM cross-references or a quote, search our online catalog or contact us.