From: <RBLevy@aol.com>
Date: Mon, 29 Jun 1998 14:45:36 EDT
To: grumman-gang@xmission.com
Subject: Re: leaning 0-360

Lycoming put out a compendium of material on their engines some time
back.  For the standard engines we have in our Grummans, they tell you:

1.  Do not lean above 75% power.
2.  Above 3500 density altitude in cruise, lean to the first sign of
roughness, then enrich until smooth (usually about two clicks).
3.  Above 5000 feet density altitude it's OK to lean to peak RPM at full
throttle before takeoff.

In addition, if I'm climbing above 5000 feet DA, I'll lean to peak RPM.

If you have a 4-cylinder EGT system, go ahead and lean at any altitude
when you're in cruise mode, i.e., 75% power or less.  I lean until the
first cylinder peaks on our JPI EDM-700, then enrich until that cylinder
is slightly below peak EGT.  I also lean in the climb until I see all
four EGT's coming up, but keep a VERY careful watch on the CHT's. 
Without that cross-check, I don't lean in the climb below 5000 feet DA,
and I do not lean to peak -- just enough to see a rise in EGT and RPM,
and hear the engine smooth out. 

If you have a single-cylinder EGT, lean to peak and then enrich to
50-75F rich of peak, since the cylinder with the EGT may not be the
first to peak, and you want to be sure all four are not lean of peak. 

If you run 100LL in your airplane, follow the recommendations of
Lycoming's Service Bulletins L185A and L197A dated September 1988,
summarized below:

1.  After start, operate the engine between 1000 RPM and 1200 RPM until
normal operating temperatures (oil and CHT) are reached.  Below 1000
RPM, not enough heat is generated to prevent leading. 

2.  Use the following run-up procedure before shutdown: Run the engine
up to 1800 RPM.  Lean to peak RPM or just rich of the rough point,
whichever comes first.  Hold 1800 for 15-20 seconds for engines limited
to 100LL (e.g., high compression O-320's) or one minute for engines
cleared for 80 octane (e.g., standard O-320's).  Shutdown by reducing to
1200 RPM and then leaning to cutoff.  (This I have not been doing.)

Finally, lean on the ground at low power.  At 1200 RPM, pull the mixture
back until the engine begins to run rough, then back in until the RPM
peaks.  Leave it there for all ground ops except run-up.  Just make sure
that "Mixture - RICH" is part of your runway line-up checks for takeoff. 

Ron Levy Cheetah N9764U