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Re: valve seats 99t Posted by Gary Stottler [Email] ![]() ![]() In Reply to: valve seats 99t, NLviking, Tue, 6 Nov 2012 23:32:45 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Yes, they are "hardened" in the terms we normally think of (that is, they are compatible with unleaded fuels), however....
Valve seat wear was a big problem in 1978 and I think 1978-80 engines also. There was a revised Exhaust valve introduced (maybe 1981?) with a thicker "throat" (since the originals tended to stretch and in severe cases the head of the valve would break off) and a different profile to reduce the risk of burning. Also, the profile for cutting the seat was modified from a 3-angle cut to a 2-angle cut to provide a wider sealing surface with better heat transfer. Bottom line: any engine you have the head off of, you should definitely make sure it has the later seat cut and, if possible, the later valves. Contact me off line and I can send you a scan of the info. Also, I would always change the valve guides as well - there tended to be a lot of exhaust valve guide wear along with the seat wear. In my opinion, the seat wear, the guide wear, and the valve stem stretching were all a result of poor heat transfer to the seat in the early engines.
Hope that helps!
Best,
Gary
posted by 198.208.25...
_______________________________________ Gary Stottler
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