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Valve Jobs Done Right. A close-up of a Honda CB750 SOHC valve seat. Though the upper 30 degree and the lower 60 degree shapes have been rough cut using Neway cutters, the 45 degree cut in the middle, the one that counts because it is the actual sealing surface, has the benefit of a stoned surface, the best possible with hand tools. Ah, valve jobs.
Valves and seats will usually have the same angle to mate properly. That angle is usually 45 degrees, but 30 degrees can be found in many modern applications. The mating angle is often accompanied by top and bottom angle cuts that are 15 degrees deflection each side of the mating angle.