The valve cone angle is the angle of the valve sealing surface, which is generally 45°, and some are 30° (CA1091 automobile 6102 engine). The valve of 30 is considered to have the same lift, the valve taper is small, the valve passing end face is large, and the intake air is large. The resistance is small, but due to the thin valve head edge with small taper, low rigidity, poor sealing and thermal conductivity, it is generally used for intake valves. The thickness of the valve edge is generally 1~3mm to prevent damage to the valve seat during work or being burned out by high temperature. In order to reduce the intake resistance and improve the cylinder intake efficiency, the intake valve of most engines is larger than the exhaust valve. The used intake and exhaust valves are also different colors. The valve stem has a cylindrical shape, reciprocating continuously in the valve guide, and its surface must be heat treated and polished. The shape of the end of the valve stem depends on the fixing form of the valve spring. The commonly used structure is two halves of the locking piece to fix the spring seat, the end of the valve stem has a ring groove to install the locking piece, and some are fixed with a lock pin. There is a hole for installing the lock pin.