David Megginson wrote in message ...
(John Galban) writes:

I've seen exhaust valves from engines that were run at high power
settings while leaned to just below peak. They were not pretty (and
would not hold compression).

Was it heat damage? I'd imagine that they'd be even worse if they
were leaned to just above peak.


Yes, it was heat damage. The plane in routinely ran leaned at about
85% power for about 150 hrs. Two of the 4 exhaust valves were
toasted.

On a well instrumented engine you could probably get away with
leaning at higher power settings. I think the reason Lyc. puts the
limit at 75% is that the average spam can does not have enough
instrumentation to keep all cylinders in the green during all types of
operation.

John Galban=====N4BQ (PA28-180)