Funny thing about that...


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Posted by Brian in Oregon on Wednesday, October 25, 2000 at 21:42:08:

In Reply to: Re: One more thing... posted by 79powerwagon on Wednesday, October 25, 2000 at 16:09:53:

I've put many miles on heads that did not have hardened seats. These were from the late 60's. Yet they survived on unleaded gas.

I believe the iron is better in later heads. However, it may be possible that also the surface is harder, and after cutting the valve seats to a certain point, they get softer.

I can't explain why some heads never have a problem with unleaded, and yet someone else with the same exact head does.

One of the problems with hardened inserts is the lack of effective heat transfer off the valve. Many racers shun hardened inserts, perferring to junk the head when wear reaches the point where a hardened seat would be needed. This is to keep exhaust valve temps down. Intake valves don't have the problem as much as the exhaust valves from heat or wear.

Now, whether this is a problem with engines that are not run on the edge (ie - raced) is controversial. For the most part, I don't think hardened seats effect valve temperatures critically on a normal street engine. On an engine that sees heavy tow use, high cylinder pressure loading and excessive heat, I think they might be undesirable.

There are probably two curves at work here, crossing at some point when the benefits of seat inserts are outweighed by the drawbacks.



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