The task of the piston is to ensure the closure of the piston on one side and to transfer pressure to the piston rod. The piston thus transfers heat to the cylinder walls.
Pistons can be made from aluminum alloys, and also from cast iron. As a rule, pistons are made by casting half of which is processed to special dimensions. Finishing of the piston top depends on the engine’s operating principle. Based on the data, it can be concluded that cast iron pistons are used for higher power engines and aluminum alloy pistons for lower power engines.
The piston is connected to the crankshaft through the connecting rod. Directly in front of the crown of the piston, along its circumference, there are channels in which the piston rings are located. The piston is mechanically and thermally heavily loaded, because during expansion it transmits pressure and heat. In the case of two-stroke engines, in addition to sealing the cylinder with the piston and piston rings, the working mixture, i.e. the burnt gases, is also separated at the same time.
The function of the piston rings is very important for the operation of the engine.
There are two types of piston rings:
• compressions
• smearing
Compression rings are located closer to the top of the piston and their task is to ensure a seal between the piston and the cylinder, so that the gases do not get from the combustion chamber into the engine housing.
Lubricating piston rings should provide lubrication between the piston and the cylinder. Most often, they have slits around the circumference through which the oil returns to the engine housing through the opening on the piston.
Piston rings are made of special cast iron. The material from which they are made should have properties that should not allow rapid wear of the piston rings. It should also ensure the elasticity of the piston rings for a better fit on the cylinder walls, and thus a better seal between the piston and the cylinder. The piston rings must have adequate clearance in the channels, both axially and radially.
