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What Is a Piston Ring Compressor?

By Lori Kilchermann
Updated May 17, 2024
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A piston ring compressor is a tool used to compress the piston rings onto a piston in order to fit the piston inside of the cylinder walls. Typically manufactured of a spring steel or a machined aluminum ring, the piston ring compressor is usually oiled well to allow the piston and rings to slide through it with ease. There are two basic styles of compressor: the adjustable type that can be made to fit many different-sized pistons, and the non-adjustable type that is made to fit one specific application and sized piston.

Piston rings are the component in a piston driven engine or motor that actually contact the walls of the cylinder. The piston rings are also responsible for creating the compression required of a piston engine to run. Made of spring-like steel material, the piston rings must be squeezed tight in order to fit inside the cylinder walls. By using a piston ring compressor, a mechanic is able to compress the oversize piston rings so that the piston will slip inside of the cylinder wall. As the piston exits the compressor, the piston rings expand out of the piston ring grooves and presses firmly against the cylinder walls of the engine.

As the piston rings are placed onto the piston, the gaps in the end of the piston rings are mismatched so as to not align perfectly with each other. This creates increased cylinder compression resulting in increased horsepower for the cylinder. The cylinder wall is lubricated, as are the piston and rings, to allow the unit to slide freely inside of the cylinder when installed. The piston ring compressor is placed around the piston and tightened, if applicable. The piston, connecting rod and piston rings are then placed into the cylinder until the compressor makes contact with the top of the cylinder block.

With the piston poised at the top of the cylinder and the ring compressor tool flush with the cylinder block, the piston is tapped into the cylinder with the wooden handle of a hammer or a similarly soft, yet sturdy, object. The piston should slide smoothly out of the compressor and into the cylinder. If a problem should occur, the piston is removed, checked and reinserted if it is in good condition. Occasionally, a ring will slip past the piston ring compressor and catch on the top edge of the cylinder. This can cause damage to the piston ring and in many cases forces the replacement of the ring to make sure the engine will operate without damage.

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