Piston rings

The piston ring is essentially a seal with a spring-like property.Similar rings are also used in other Piston
and cylinder mechanisms,such as compressors or hydraulic devices.The piston ring of an internal combustion engine must be designed with sufficient heat resistance to withstand exposure to high temperature gas.

The piston ring must have the following
functions :

Sealing of combustion gas - Airtight with low
tension - Light weight - Preventing fluttering -
Corrosion resistance

The upper rings are compression rings which
are forced outward against the Cylinder wall
and downward onto the groove face.

The lower rings scrape the surplus oil from the
cylinder wall and return it to the crankcase.

The crankcase must be ventilated to remove
gases which blow by the piston rings, to prevent
pressure buildup.

The ring belt usually has three or more rings . Two cycles engine do not required oil rings and therefore may have only two rings .ring lands are located between the ring groove .

The top land ,or first land is located above the first ring . the second land is heavy because it supports the first ring and bears the majority of the pressure and thermal loading of the belt .the second and third lands
are lightly loaded . because of expansion of the piston top at operating temperture , the ring lands are usually relieved or cut smaller in diameter than the rest of the piston .

So we can say that The main functions of piston rings are :

(1) To form a pressure seal, preventing blow-by of the gases, including combustion products at high
     temperatures.

(2) Control of the flow of oil in enough quantity to the skirt and to the rings themselves, while preventing
     excessive amounts from entering the combustion chamber.

(3) The transfer of heat from the piston to the cylinder walls.