The functions of the engine cylinder head are: 1. Close the upper part of the cylinder to form a combustion chamber; 2. It is the support of camshaft, rocker shaft and intake and exhaust pipe; 3. The air is sucked into the cylinder, and the combustible mixture is ignited by the spark plug to drive the piston to do work, so that the exhaust gas is discharged from the exhaust pipe. There are two common types of engine cylinder head: 1. Side valve engine cylinder head, cast with water jacket, water inlet hole, water outlet hole, spark plug hole, bolt hole and combustion chamber; 2. In addition to the cooling water jacket, the cylinder head of overhead valve engine also has valve device, inlet and exhaust channels. Common faults are that the valve clearance is too large or too small, resulting in abnormal valve noise or failure of camshaft position sensor on cylinder head.