A piston ring is a split ring that fits into a groove on the outer diameter of a piston in a reciprocating engine such as an internal combustion engine or steam engine.

1. Sealing the combustion chamber so that there is no transfer of gases from the combustion chamber to the crank. 

2. Supporting heat transfer from the piston to the cylinder wall.

Procedure for replacement of rings:

Replacing piston rings requires removing the pistons. To this effect, the cylinder head must be removed from the engine block, followed by the sump. After unscrewing the connecting rod ends, the pistons and the connecting rods can be removed from the top through the cylinder openings.

When fitting new rings, have the pistons inspected and ensure that each piston ring is properly locked. Fitting the pistons equipped with new rings in the cylinders requires using a special tool called the piston ring compressor. When screwing the connecting rod to the crankshaft you should have the pans located there inspected.