To the lister asking about fuel additives:
I have never used any lead substitute additives. Came to the conclusion that it
is not a significant near term issue. Whenever I have an engine that gets
pulled for a rebuild, I have hardened seats installed.
SAE reported on a major study years ago on the effect of unleaded gas on valve
seats. Study used two types of fleet vehicles - taxis and tow trucks. The
assumption being that these vehicles were at the extreems of the spectrum of
street use. Namely high idle time and high load respectively. Study concluded
that the lack of lead in the gasolene did have an effect on valve seat recession
on engines operating under a SEVERE load, but that this was not a major concern.
The service life between valve seat replacement (valve job) might be reduced by
up to (approx.) 20% over the same engine using leaded fuel or having hardened
valve seats.
So far, I have never had to do a valve job because of valve seat recession.
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