ORIGINAL: downunder
The main reason I've started this thread is to condense the 5 (so far!) pages of the original (BTW, I loved the part about "it's hard to hit a moving target"
).
I'm glad I was able to provide a bit of humor.
But to sum up, we've all heard that if a new, unrun ABC is run too rich from the getgo or even during the break in period for any length of time at all then there's a likelihood that this rich (as in 4 stroking rich) running could cause immediate and permanent damage. This damage can be anything from excessive wear on the piston through to breaking rods because of "compression-tension" cycling of the loads. However, I'd never seen anything by any manufacturer specifically warning against running in a 4 stroke, they all seem to say run it rich but there's never a proper definition of "rich". The closest I've seen was a point barely above the break from a 4 stroke into a 2 stroke mode. Now this is fine if you've run engines before and know what the 4 stroke sound is like but what does a newbie do? All he knows is that the engine is running and makes a noise. Now very few newbies will go out and buy a Jett, Nelson or Profi as their first engine so all this talk about damage is directed against sport type engines.
For reference, here's what K&B says about running an ABC engine too rich:
ABC engines are designed to run at operating temperatures, NOT COOLER temperatures. RUNNING THE ENGINE TOO RICH WILL RUIN THE FIT. If the operating temperature is not reached, the piston is prematurely worn from lack of clearance. You do not want to "break-in" an ABC engine at a very rich setting. Just a slightly rich setting for the first 30 to 45 minutes of running is adequate.
And about break-in and running:
A model engine makes sounds that will tell you how it's performing. You'll have to listen very carefully for them, recognize their message, and make adjustments to the fuel control needle valves accordingly. The mixture of fuel and air is controlled by the amount of fuel metered by the needle valve.
SLOPPY RICH MIXTURE running is characterized by a very slow, irregular, sputtering exhaust sound. The exhaust gas will be very smoky and contain many droplets of oil. NEVER RUN AN ABC ENGINE AT THIS SETTING. The cylinder is not able to heat properly and the fit will be ruined in a short time.
RICH MIXTURE running is characterized by a slower, sometimes irregular, sputtering exhaust sound. The exhaust gas will be smoky and probably contain small droplets of oil. NEVER RUN AN ABC ENGINE AT THIS SETTING. The cylinder is not able to heat properly and the fit will be ruined in a short time.
FOUR CYCLING or SLIGHTLY RICH running is a rich type setting, but it is fast enough to pull the airplane. This is the setting you normally look for before launching the airplane because the engine will run leaner when airborne.
PEAKED OR TWO CYCLE. As the main needle is closed (clockwise), it reduces the amount of fuel mixed with the air drawn into the engine. At a specific point, which varies with each engine, air temperature, altitude and relative humidity, the exhaust note will change quickly into a smooth, powerful note. If the needle is closed further, the note will stay smooth, but will weaken. The peak occurs just at the break point from a rich setting and further leaning will ruin the engine. A lean setting raises the engine heat above the safe point, reduces lubrication, and destroys glow plugs due to high combustion temperature. This is very harmful to the engine and your investment. Learn to tune the engine before flying. Remember, a little rich is always preferred for long motor life.
AIRBORNE BREAK-IN
1> BREAK-IN running should be done with the recommended propeller at a slightly rich setting. You want the engine to be at running operating temperatures. The needle valve should be set at a point just into this range from a four cycle setting. Fly the plane at maximum throttle for 2 minutes, then throttle back to half throttle for approximately 30 seconds. Repeat this sequence until approximately 20 minutes of accumulated running time has been obtained. Additionally, certain maneuvers, such as "CUBAN EIGHT'S", that allow the engine to load and unload are recommended. AVOID PROLONGED CLIMBING MANEUVERS AT MAXIMUM THROTTLE.
2> After the first 20 minutes change to normal size prop and fly an additional 15 minutes. Continue to run the engine at a slightly rich setting and fly your normal pattern.
3> After the above break-in period, run the engine at a normal peak needle valve setting. This should be a little on the rich side because engines run leaner in the air. 5% - 15% nitro may be used.
BENCH BREAK-IN
NOTE THAT THE ENGINE MUST BE FIRMLY MOUNTED ON A SOLID TEST STAND. DO NOT CLAMP ENGINE IN A VISE. Muffler may be used during bench break-in.
The initial bench break-in period is also approximately 15 minutes (15 minutes bench and 15 minutes airborne). During this time, use the recommended break-in propeller and run the engine at a slightly rich setting. It is best to run the engine for a full 10 minutes, then allow it to cool. Heating and cooling is not beneficial to an ABC engine as you what it to run at operating temperatures, not cooler temps.
1> Start the engine and run it at a rich full throttle for about 2 minutes, then let it fast idle (about 3500 rpm's) for 30 seconds. Repeat this sequence for about 10 minutes of running time.
2> Increase the full open throttle time to about 3 minutes followed by a 30 second idling period. Do this for an additional for 20 minutes.
3> Install the engine in your aircraft using an normal size prop.
The manuals for several other ABC engines I own also warn that running the engines too rich will cause damage, premature wear, etc. These engines include Webra and a Tower .75.
I'm in complete agreement with XJet, there are plenty of warnings against running ABC engines too rich, so "why take the risk?"