The engine is composed of two parts of the cylinder block and cylinder head, which are connected to each other by bolts. If the quality of the cylinder block and cylinder head is good, the cylinder data should have satisfactory strength, good castability and machinability, and the price should be low, so the commonly used cylinder data are cast iron and alloy cast iron. Cast iron has many congenital shortcomings, such as large weight, poor heat dissipation, high friction coefficient and so on. So cylinder block and cylinder head manufacturers are looking for more suitable data, such as aluminum with a lower density than iron. Now the cylinder block of aluminum alloy is more and more widely used. because the weight of aluminum alloy cylinder is light and the thermal conductivity is good, the capacity of coolant can be reduced. After the car is started, the cylinder block quickly reaches the high working temperature, and the expansion is exactly the same as that of the aluminum flower plug, and the gap becomes very small after heating, which can reduce the strong noise and oil consumption caused by the impact. In the same situation, aluminum also has disadvantages, it is easier to react with the water produced during combustion, and the corrosion resistance is not as good as that of cast iron cylinder. There are three structural types of cylinder block and cylinder head water-cooled automobile engine: no cylinder liner, dry cylinder liner and wet cylinder liner.
