Disesel engine truck part ISBE 4089258  piston ring 

The main functions of piston rings in reciprocating engines are:

1. Sealing the combustion chamber so that there is minimal loss of gases to the crank case.
2. Improving heat transfer from the piston to the cylinder wall.
3. Maintaining the proper quantity of the oil between the piston and the cylinder wall
4. Regulating engine oil consumption by scraping oil from the cylinder walls back to the sump