In order for a valve guide to function optimally, it must be dimensionally correct. More significantly however, it must be manufactured from the correct material.
Correctness in dimensions allows the valve stem the optimal clearance in the valve guide bore. The outer diameter of the valve guide must be finely ground to a very specific dimension, to ensure the correct fit into the cylinder head, which in turn, compresses the bore to give the required bore to valve stem clearance.
The finish and fit of the outer dimension ensures maximum heat dissipation from the valve stem through the valve guide wall and then into the water cooled cylinder head. This chain of events protects the valve and prevents premature wear on the seating area, thereby retaining compression and ensuring the efficient burning of fuel.
Most valve guides are made from a highly alloyed cast iron that has a phosphorous content, which creates microscopic porosity in the microstructure. This minuscule porosity, which escapes the human eye, actually holds oil and thereby self-lubricates the valve stem in what is a very aggressive operating environment. Our in-house foundry produces the raw materials required to OE specifications for both heavy diesel and petrol applications.
Certain engines such as Porsche, Mercedes Benz, Audi, BMW and VW use a sophisticated copper zinc alloy in the manufacture of their valve guides. Microfinish also has access to this specific material, which complies with OE manufacturing specifications for valve guides.