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Remote Name: 192.168.2.1
Date: 10 Feb 2005
Keith, you have successfully argued both ways, but I am not sure that we are any closer to a good answer that will serve to guide us for future engine builds. One point I would make is that it is normal practice (to my knowledge) to grind a differential angle between valve and seat. That is to say, the exhaust valve seat in the head will be 45° (included angle of 90°) and the seat angle on the valve will have an included value of say 43° so that you get a narrow but positive seal around the periphery. As the valve wears in, the seat migrates to a wider and wider band, but it is still a positive seal. I don't think that lapping valves in is a widely condoned practice nowadays, at least certainly not heavy lapping to create a wide seat band. Yes, I know that a narrow seat makes it harder for the valve to shed the heat, but a lot is conducted away through the stem/guide interface. Perhaps the answer is to use the Jowett information as a guide, and take advice from your auto machine shop. They will be familiar with both traditional and modern practice.