The International Cessna 170 Association

What are your techniques for leaning the C-145/O-300? I generally climb full rich and once level and at cruise speed, slowly pull the mixture and watch RPM. Once RPM peaks and begins to drop, I push the mixture back in until it peaks and just begins to drop off.

What about on the ground? Do any of you lean on the ground prior to takeoff? Always? Or only at higher airports?

I fly in FL and the fields I operate in/out of are rarely above 150' and usually less than 50' field elevation. Recently, my airplane sat for about 6 months while I was away for work and prior to getting my annual done last year, I ran the engine for about 30 minutes. Once warmed up, I varied the RPM periodically and performed a couple of mag checks. I also played with the mixture using the same technique as I use at cruise and noticed improved performance - smoother & crisper.

Despite this, I still takeoff and climb full rich, but curious if others do any leaning on the ground prior to takeoff?

I use pretty much the same process as Aryana. Has served me well. I don't have the EGT/CHT (yet), so it is nice to know this method works as well as/better than going by EGT alone.

I lean like Arash as well except that I only have a tach and my ears to guage peak power.

The problem is that 100LL has roughly 4 times the lead as 80/87 avgas which is no longer generally availible. (The O-300 was designed to use 80/87 fuel with a mimimun 80 octane way back when.) The additional lead in 100LL will rather quickly foul your plugs if you run a rich mixture on the ground for prolonged periods, leading to rougher operation and more frequent spark plug cleaning.

The solution to minimize the problem is to be vigilant about leaning on the ground, leaning in climb and cruise as appropriate, and perhaps use a lead scavaging product like TCP. (I don't bother any more with the TCP.)

How lean is too lean? If the engine dies when you advance the throttle to taxi, its too lean.

Don't worry about detonation on the ground from being too lean with 100LL. At low power settings for taxi operations, its not going to happen. At high power settings in flight, its still not likely to happen when using 100LL because of its higher octane rating but don't temp fate.

Just don't forget to go to full rich on take off or you might have the engine die when its inconvenient. Lean in climb per the owners manual.

High density operations are an exception and will require leaning carefully to max noise before take off with subsequent adjustments as you climb.

Leaning if using unleaded auto gas is beyond the scope of this note and should be addressed separately if you are interested.

Both the Owner's Manual (Section III) and the Continental Operator's Handbook, Operating Instructions, Para 5, say to set cruising RPM (recommended 2450) and adjust mixture by leaning to obtain maximum RPM with fixed throttle, then return toward Rich until RPM drops just perceptibly.
This provides a "Rich-Lean" condition.

I do not have EGT indicator.

I only lean for takeoff at high density altitudes, otherwise operate TO and Climb full Rich, leaning for climb above 5K altitude.
Once cruising, I use the recommended procedure in an earlier version of the Operator's Manual. I set RPM and lean until RPM just begins to drop-off, then return mixture to the Max RPM plus-one-click Rich (I have a ratcheting mixture control and this technique is Rich-Lean but does not indicate a loss of RPM), and leave it at that setting throughout descent until entering the terminal area, where once levelling off, re-lean as at cruise. (Obviously, if cruising altitude or power is altered, I completely re-accomplish the leaning procedure.)
On final approach, before power reduction I apply carb heat for sufficient time to assure myself no carb ice has accumulated, then carb heat off for the remainder of the final approach and landing. I leave mixture at the "terminal-area" re-leaned condition all through landing and taxy-in, but am cognizant of needing to en-RICH in the event of go-around.

I do not lean for taxy-out but see no harm in doing so as long as mixture is re-set for takeoff.

After landing, I ALWAYS allow the engine to idle (800-1000 RPM) for TWO MINUTES to stabilize temperatures before cutting the mixture. It is my opinion that the techniques I use reduce fouling and avoid sticking valves.

(Avoid idling below 600 RPM to ensure upper cylinder and piston lubrication from crankshaft "oil sling". This can be even more likely when an engine is cold. 800 RPM is recommended after start.)

We have a sophisticated and complex leaning method.

Partner Leroy pulls the mixture control out the distance from the tip of his index finger to the top knuckle of the same finger. It's the way he's done it every flight for the last 49 years. And his engine ran fairly trouble free since it's last overhaul he did 48 years and 1830 hours ago.

We compared my index finger to his and find it the same length from tip to top knuckle and so I do exactly the same.

I do exactly as Arayana does except I go for lean of peak due to too much lead in the system .

Leroy and I must have gone to same school. He, Bruce and I use same method. I have owned 15d for 33 years and method has not failed me yet.

TIMEOUT. We have 3 people who agree exactly how to do a procedure. This is a first. And it must be therefor the best practice. As I doubt anyone could find another technique followed exactly by 3 or dare I say, 4 people.

For those who want to jump on the best practice bandwagon but think they need something just a bit more exact to feel comfortable with it. It is acceptable to substitute a quarters width for an old fashion finger section.
So long as it was minted in 1993.

Ever since the Alamo.... Texans give "No Quarter".

Note: Jim, LeRoy and Bruce posted their club on April Fools Day. Join them at your own risk.

Auto-Lean is STC'ed for the C-170. Only $900.

I have a O-300/A that is equipped with a 6 cylinder engine monitor. I have owned this airplane for 9 years and have flown over 1000 hours behind this engine. I have tried multiple leaning techniques and have found they all produce the same results.

1. Pull 1 knuckle's worth mixture in cruise puts be within 10% of best mixture 90% of the time.

2. Lean feature using engine monitor.

3. Select one magneto. Lean till rough, both magnetos back on.

4. Lean until rough then enrichen to smoothness.

5. Lean to max RPM when needed for performance or to takeoff above 4K' DA.

The engine monitor is nice to be able to see specifics, but really doesn't help with the exception of partial leaning in a climb, where it allows one to monitor CHT's.

Jughead