The Lycoming geared engines have acquired a bad reputation over
the years – quite undeserved. These are very solid, reliable
engines, but only if operated correctly! If operated like the
engine on your Cessna, they have a tendency to be quite short-lived
and very expensive. Treated with tender care and flown by someone
who knows how to operate the engine, they reliably make TBO time
and time again. Tips to make TBO:
This information has been derived from MANY conversations
with MANY very knowledgeable people including freight operators,
air-taxi seaplane pilots in Alaska, Lycoming engineers,
and Aero Commander "old-timers" from Oklahoma City. It has
been verified by many Lycoming shops also.
In a nutshell, the secret to long life of your GO-series
Lycoming is to NEVER EVER let the air turn the prop! Although
the Lycoming planetary gearbox is pretty stout, things really
begin to bang and clatter if you don’t have a solid, positive
ALWAYS keep the manifold pressure up.
You’ll be able to hear the gearbox "whining" if you come down
final at too low a throttle setting.
Don’t push the prop levers forward upon arrival at an airport
I know this probably goes against everything you were ever told
by your instructors, but when running a GO-series engine, you’ll
be doing the gearbox a BIG favor by keeping the RPM back to 2700-
2800 until landing. If you need to go around, it’s perfectly safe
to advance the throttle fully before bringing the RPM up – unless
you’re running a supercharged engine. ie: GSO-480, etc
Keep your idle speed up.
Much below a 1500 RPM idle will "chatter" the gearbox causing
VERY rapid wear of the outer planetary "ring-gear". This is
a horribly expensive part to replace by the way. Last new one
I found was $3500!
Move the throttle levers VERY slowly!
Lycoming recommends a MINIMUM of 30 seconds from fast idle to
takeoff power. FOLLOW THIS RULE! When going the other way, go
even slower 🙂
If your GO-series engine has a Bendix pressure carb, follow the
operator’s book: maintain FULL power during climb. The Bendix
carb has an "auto-rich" compensation circuit that allows the engine
to run rich at full throttle setting. If you pull the throttle
back during initial climb, the carb goes "auto-lean" and you will
risk over-temping the engine. Again, follow the book!
This is the single biggest killer of any aircraft engine in my
honest opinion. Lycoming engines especially, suffer greatly from
non-use. Corrosion on the cam lobes, cylinder rust, and valve
damage occur rapidly on engines that don’t run frequently.
How to tell if you need an overhaul
there is a service bulletin that specifies an allowable
play measured on the prop. You are allowed 1/2" play at a location
4 feet from the center of the prop (radius). Just take a tape measure,
make a pencil mark at the point on the blade 4 feet out from the
center of the spinner. Place the tape measure on the ground with one
prop blade in the horizontal position and measure how much "slop" you
have in the gearbox.
Having been through several gearboxes, there is another issue that
I have noted. If you have a distinctive "stop" at each end of the
range of movement of the prop, then chances are that everything in
the gearbox is OK. If there is more than one "clank" or contact when
moving the blade around, the plate that holds the stationery gear
_may_ have partially sheared the attach bolts. Worn gears are not
going to self-destruct, but if that stationary gear shears the bolts,
then the whole gearbox may come completely unglued! Although I have
not witnessed this myself, I have heard that it can be pretty exciting.
A "CW turn-clunk, CCW turn-clunk" check is always part of my preflight.
So, there you have it. Follow the above steps, and you will have
a happy motor. I won’t guarantee TBO, but I can assure you that
your next overhaul will be much cheaper if you don’t have to replace
everything inside of that expensive