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Re: Error Noted in Technical Manual?

Category: Technical
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Date: 10 Feb 2005
Time: 01:25:28


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.

Last changed: November 19, 2008