Valve guide

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Valve guide" – news · newspapers · books · scholar · JSTOR (March 2007) (Learn how and when to remove this message)

Valve guides are cylindrical metal bushes, pressed or integrally cast into the cylinder head of most types of reciprocating engines, to support the poppet valves so that they may make proper contact with its valve seat. Along with a corresponding valve spring, they are one component of an engine’s valve train.

Guides also serve to conduct heat from the combustion process out from the exhaust valve and into the cylinder head where it may be taken up by the cooling system. Bronze is commonly used, as are various iron alloys; a balance between stiffness and wear on the valve is essential to achieve a useful service life.

The clearance between the inner diameter of the valve guide and the outer diameter of the poppet valve stem is critical for the proper performance of an engine. If there is too little clearance, the valve may stick as oil contaminants and thermal expansion become factors. If there is too much clearance, the valve may not seat properly and excessive oil consumption can occur.