The function of the piston is to form the combustion chamber together with the cylinder head, the cylinder wall, etc., and bear the gas pressure in the cylinder. The force is transmitted to the connecting rod through the piston pin to drive the crankshaft to rotate.

Piston head:

The piston is a component of the combustion chamber, and its shape depends on the form of the combustion chamber. Common piston head shapes include flat-top, concave-top, and convex-top.

Piston ring grooves:

The piston rings are installed in the piston ring grooves. Gasoline engines generally have 2 to 3 ring grooves. The top 1 to 2 grooves are used to install gas rings to achieve the sealing of the cylinder; the bottom one is used to install the oil ring. Many radial oil return holes are drilled on the bottom surface of the oil ring groove. When the piston moves downward, the oil ring scrapes off the excess engine oil on the cylinder wall and flows back to the oil pan through the oil return holes. If the temperature is too high, the first ring is prone to carbon deposits and overheating and jamming.