The sleeve or cylinder liner is a high-temperature-resistant alloy work, which is inserted into the engine block, and in smaller engines it can be part of the block, i.e. cast together with the engine block.
Its role is to accept the heat generated by combustion and transfer it to the environment through the coolant, and also to accept the forces that develop during combustion and the movement of the piston.
Liners of two-stroke and four-stroke engines differ in design, in the case of two-stroke engines, they have channels for changing the medium at its lower part, while the liners of four-stroke engines do not.
