Valve Guides
Valve guides play a critical role in the function of today's internal combustion engines. They are responsible for the proper function and alignment of engine valves which are required for introducing air for combustion or eliminating the post-combustion exhaust gases from the cylinder.
In order for a valve guide to function properly, it requires a level of surface texture and porosity to maintain a balance of proper lubrication (contained by porosity) and a bearing surface to maintain contact with the valve rod. All these factors must be considered when under high frictional stress which generates large amounts of heat.