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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.
Installed height is determined by how much the spring is compressed to arrive at proper seat pressure. Open pressure is the pressure exerted on the valve when it is in the open position, while seat pressure, the most critical, is the amount of pressure exerted on the valve while it is on the seat.