Cylinder: The cavity in which the piston is placed on the cylinder of an internal combustion engine. It is the orbit of the piston movement, in which the gas burns and expands, through the cylinder wall, it can also dissipate part of the explosion waste heat transmitted by the gas, so that the engine maintains the normal operating temperature. The type of cylinder has integral type and single casting type. Single casting type is divided into dry type and wet type. When the cylinder and the cylinder block are cast as a whole, it is called an integral cylinder; when the cylinder and the cylinder block are cast separately, the single-cast cylinder barrel is called the cylinder liner. The cylinder liner that directly contacts the cooling water is called a wet cylinder liner; the cylinder liner that does not directly contact the cooling water is called a dry cylinder liner. In order to maintain the tightness of the contact between the cylinder and the piston and reduce the friction loss of the piston moving in it, the inner wall of the cylinder should have a higher machining accuracy and precise shape and size.