Valve Guide

The function of the valve guide is to guide the movement of the valve to ensure that the valve performs reciprocating linear movement, so that the valve and the valve seat ring can fit correctly, and the heat of the valve stem is transferred to the cylinder head.
The operating temperature of the valve guide is also relatively high, about 200°C. When the valve rod moves in the duct, it is lubricated only by the oil splashed out of the valve mechanism, so it is easy to wear. Therefore, nodular cast iron or powder metallurgy materials with self-sliding properties are often used to make separate parts, which are pressed into the valve guide seat hole on the cylinder head with a certain interference to prevent falling off. In order to prevent the valve guide from loosening, some engines use snap rings to fix and position the guide.
The lower part of the valve guide extends into the intake and exhaust ducts. In order to prevent resistance to the air flow, the outer circle of the extension end is made into a conical shape. There is a gap of 0.05～0.12mm between the valve guide and the valve stem, so that the valve stem can move freely in the guide.