Valve guide

Valve guides are cylindrical metal bushes, pressed or integrally cast into the <a href="/facts/Cylinder_head/K0RJ8mxT">cylinder head</a> of most types of <a href="/facts/Reciprocating_engine/ItLAxmW3">reciprocating engines</a>, to support the inlet valve and exhaust valve stems. So that they may make proper contact with its <a href="/facts/Valve_seat/xUS65zxs">valve seat</a>. Along with a corresponding valve spring, they are one component of an engine’s <a href="/facts/Valve_train/PMAR1vSR">valve train</a>. 
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. <a href="/facts/Bronze/YCYCVIKt">Bronze</a> is commonly used, as are various <a href="/facts/Iron/QK1JYy8E">iron</a> alloys; a balance between stiffness and wear on the valve is essential to achieve a useful service life. <a href="/facts/Powder_metallurgy/tv9uXamF">Powder metallurgy</a> materials are also commonly used in the manufacture of valve guides, which have the advantages of flexible material composition and the self-lubricating properties.
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.

Valve guide open-in-new

Valve guide