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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.
A 60 degree bottom cut sets the width of the 45Â°seat. The 45Â° exhaust seat is deliberately kept inboard of the outer edge of the valve â otherwise hot exhaust gas will eventually erode the edge of the valve. The diagram below shows the three angles: 30Â°, 45Â° and 60Â°: 3 angle valve job.