The cylinder liner is inlaid in the cylinder barrel of the cylinder block, and the combustion chamber is composed of the piston and the cylinder head. In early water-cooled internal combustion engines, cylinder liners and water jacket walls were cast as a whole without cylinder liners. The inner wall of the cylinder directly guides the piston, while the outer wall of the cylinder is cooled by cooling water.
Cylinder liners are classified into dry and wet liners.


        The cylinder liner that does not touch the cooling water on the back is called the dry cylinder liner. The cylinder liner that contacts the cooling water on the back is the wet cylinder liner. Dry cylinder liner is thin in thickness, simple in structure and convenient in processing. The wet cylinder liner contacts the cooling water directly, so it is beneficial to the cooling of the engine and the miniaturization and lightweight of the engine.
        Dry cylinder liner does not contact with coolant directly, and its wall thickness is generally 1-3 mm. Both the outer surface of the cylinder liner and the inner surface of the cylinder liner seat holes need to be finely machined to ensure the necessary shape and position accuracy and to facilitate disassembly and assembly. Because the wear of the cylinder wall is not uniform along the height, usually the greatest wear always occurs near the top dead center of the piston, so some dry sleeves are not made as long as the cylinder, but only part of the length. The advantage of dry cylinder liner is that the rigidity of cylinder block is large and the distance between cylinders is small. It can ensure good water sealing without cavitation. The disadvantage is poor heat transfer, uneven temperature distribution, easy to occur local deformation; at the same time, more processing surface, high processing requirements, disassembly and assembly requirements are also high.
Wet Cylinder Liner


        The wet cylinder liner is in direct contact with the coolant, and its wall thickness is usually 5-9 mm. There are two prominent ring bands outside the cylinder liner to ensure radial positioning, which are called upper support positioning band and lower support sealing band respectively. Axial positioning of cylinder liner is based on the upper flange. In order to seal gas and coolant, some cylinder liner flanges are also equipped with copper gaskets. The diameter of the upper supporting positioning belt of the cylinder liner is slightly larger, and it fits tightly with the cylinder liner seat hole. The lower support seal belt is loosely matched with the seat hole. Usually there are 1 to 3 rubber sealing rings to seal the coolant. There are two common sealing structures: one is to open the groove of the sealing ring on the cylinder liner, and to put the elastic rubber sealing ring into the ring groove; the other is to place the ring groove of the sealing ring on the cylinder block. This structure weakens the cylinder liner very little, but the cylinder block is poor, so it is not as good as the first structure application. Extensive.
        When the cylinder liner is loaded into the seat hole, the top surface of the cylinder liner is usually slightly higher than the plane of the cylinder block from 0.05 mm to 0.15 mm. In this way, when tightening the cylinder head bolts, the cylinder head liner can be tightened to ensure the sealing of the cylinder and prevent the leakage of coolant and high-pressure gas in the cylinder.