Piston rings are required to create a tight but flexible alignment of the piston with the cylinder. Heat is removed from the piston to the cylinder, gases from the above-piston cavity are prevented from entering the engine crankcase, as well as the flow of lubricants into the combustion chamber.

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Since these parts are used in harsh conditions, they are made from high-strength alloy cast iron. The upper compression rings are additionally coated with porous chrome or molybdenum anti-wear insert from the outside. This is necessary due to the maximum thermal stress, which manifests itself as a result of the influence of working gases and friction against the cylinder walls with insufficient lubrication in the upper half of the piston.

The FAI AutoParts brand Piston Ring Kit usage

The mechanism can have two or three compression rings, which are located in the upper piston grooves. Thanks to a special cut or a lock with a slight backlash, they can spring and expand when exposed to high temperatures.

Depending on the design features of the engine, one, rarely two oil scraper rings are installed in order to regulate the amount of lubricant on the cylinder walls. But they do not completely remove the oil, as this can lead to oil starvation and piston sticking in the cylinder.