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2023 / 01 / 07

Three Types Of Piston Rings


There are three piston rings placed on an engine piston.
  1. Compression ring
  2. Middle ring
  3. Oil scraper ring 

Compression ring:

Compression ring is the top ring in the piston attached to its outside diameter. The main function of the compression ring is to seal the gap between the piston and the cylinder walls.

Sealing this gap with the outer diameter of piston and the cylinder walls ensure that the air fuel mixture in combustion engine does not move down to the crankcase and cause low compression and power.

Moreover, this sealing also makes sure that the engine oil in the crankcase, used for lubrication, does not move up into the combustion chamber and gets burnt.

The air fuel mixture in the combustion chamber is not allowed to trickle down into the crank case and the engine oil is not allowed to move up into the combustion chamber.
As for the advantages of compression ring sealing the gap between the piston and the cylinder walls include – maintaining high compression in the combustion chamber, high power and acceleration in the vehicle, and no unnecessary burning of engine oil.

Middle ring:

middle ring helps in sealing the combustion chamber from the crank case as well as guiding the engine oil back down to the crank case.

While it may look like the middle ring is just there as a back up for both the compression ring (the top one) and the oil scraper ring (the bottom one), we cannot stress its importance more since it performs the function both these end rings.

If the compression ring is failing or not performing, then the middle ring acts as the primary seal between the combustion chamber and the crank case. Thus, not allowing the air fuel mixture to enter the crank case and maintain engine performance.

Additionally, if the oil scraper ring is not working, the middle ring will again perform to guide the engine oil down back into the crank case through the oil holes present below the oil scraper ring. This helps in keeping the crank case component and the piston lubricated and cooled down sufficiently.

Oil Scraper ring:

The main function of the oil scraper ring is to guide the engine oil scraping along the piston outer surface back into the crank case.

Firstly, what the engine oil does is it moves up along the piston outer diameter as a result of piston’s up and down movements.

The oil scraper ring barricades further upward movement of the oil and forces it to move downward, and forces the engine oil to move downward, so it does not necessarily mean along the piston surface.

There are oil holes on the piston right below the oil scraper ring. These holes allow the engine oil which are forced to move downward to enter into the crank case through these holes.