I recently received a letter asking about engine break-in following overhaul. This is a subject that should be of interest to everyone, even though you may never actually have the opportunity to break-in an engine during your flying years.
It makes no difference whether it is a factory new, factory rebuilt, factory overhaul, or an engine overhauled in the field, the most important rule regarding engine break-in is don’t baby it! These same break-in procedures also apply if a cylinder replacement takes place during the life of the engine.
Every factory engine comes with information as to how an engine should be broken in following installation. Most field overhaul facilities also provide similar information, which may be more specific for their overhaul and should be followed to assure proper break-in occurs.
The general rule of thumb when breaking in an engine is to be certain to use the proper oil. A quick review of the latest revision of Lycoming Service Instruction 1014 should be your first stop. Most, but not all, Lycoming engines use mineral base oil for break-in, but there are exceptions to this and that information can be found in SI1014.
When I say “don’t baby it,” what that means is that using lower power settings for break-in is not recommended. Using full power for takeoff and climb is not harmful to the newly installed engine and serves the engine well for a proper break-in. However, all engine temperatures should be monitored closely to ensure overheating does not occur.
To get good ring seating, we must keep the power up during takeoff, climb and cruise in order to expand the piston rings and force them against the cylinder walls, which causes the ring to seat. I usually recommend the aircraft be cruised at 65% to 75% to accomplish good break-in. If the engine were mine, I’d use 75% power for cruise. You must also keep in mind that break-in should occur at altitudes typically under 5,000 feet where 75% power can be attained on normally aspirated engines. Density altitudes in excess of this will not allow the engine to develop sufficient cruise power for a good break-in.
From my experience, if an engine is operated properly, the break-in will usually take place within the first 25 hours or sooner. The key that will let you know break-in has occurred is when the oil consumption stabilizes. Once the oil consumption stabilizes, you may then switch to an AD (ashless dispersant) oil of your choice.
Once again, I cannot emphasize enough that you must read the engine manufacturer’s or overhauler’s recommended procedures for proper engine break-in. Failure to do this may cause improper break-in and cause high oil consumption and costly repairs to correct this situation.
Paul McBride, an expert on engines, retired after almost 40 years with Lycoming. Send your questions to: AskPaul@GeneralAviationNews.com.