On Jan 3, 10:10 am, wrote:
You may be exactly right. Somewhat irrelevant for me, since my 1978 Cessna
172N doesn't have an EGT gauge or cylinder head temp gauges. My POH says to
lean until the tach drops 25 to 50 RPM, which I've read is supposedly
somewhere slightly lean of peak. My partners say they lean until the tach
drops off, then twist the mixture knob back rich a couple of turns. I do the
25 RPM drop-off method, but I've always been worried I might be causing
damage to the engine, based on what I've read in some of the on-line
articles people on this group recommended. Or maybe my partners are damaging
the engine by doing it their way, if not just wasting some gas. I wish
there was a way to be absolutely sure.

Lycoming says you can lean your normally-aspirated engine
anyway you like if you're at or below 75% power without damaging it.
See your cruise charts. Detonation is seldom any risk at 75% or less.

Dan