A follow-up to our recent experience with "engine infant mortality." The folks at Penn Yan Aero have worked exceptionally hard for us to turn around an engine replacement in three weeks time. The engine on one of our C172s began developing metal just a few hundred hours into its life, which was attributed to manufacturing defects, and all this was done under warranty. The plane should be back on the flight line in a few days, so now might be a good time to think about proper engine break-in—the process of getting the piston rings to properly form to the cylinder walls.
Mahlon Russell of Teledyne has a very nice piece on the "hows and whys" of engine break-ins. A very good read in its entirety. To summarize:
- Keep ground running to a minimum
- Take off at full power and reduce to climb power at the first available safe altitude
- Keep the climb angle flat and the climb airspeed higher to promote cooling
- At cruise altitude use 65% to 75% power. (Higher, and the BMEP—brake mean effective pressure—gets too high, and the likelihood of glazing increases.)
- Run the engine richer then normal.
- Remember that heat is the greatest enemy of engine break-in. Try to maintain all engine temperatures in the green, well away from the top of the green arc or red line.
- Step climb the aircraft if necessary
- Operating with the cowl flaps open or in trail position during cruise flight
- Be generous with the fuel allocation for the engine. We should not run the engine above 75% power in cruise flight because the B.M.E.P is too great and the likelihood of glazing increases.
And this should go on for the first 100 hours. All this also means no touch-and-goes, no repeated take-offs and landings, and no maneuvers like stalls or steep turns.