Some thoughts you might consider when deciding the maximum operating period for your Lycoming or Continental engine. You can follow Lycoming's or Continental's recommendations, or do your own risk assessment.
Age related deterioration might be more important on little-flown engines than engine hours.
For high-usage operators - hours are important as hours add wear and fatigue to engine parts.
For low-usage operators - time is important as corrosion and seal and hose deterioration, take their toll on engine parts. There is an inverse relationship between component age and component reliability. 1.
Powertrain - the engine's "lower end" or everything inside the crankcase.
In-service engine inspections are generally external and superficial. Engine powertrain components are not inspected. These include but are not limited to:
Engine Bearings (deterioration not detected through oil analysis)
Counterweight bushings (deterioration not detected through oil analysis)
Camshaft lobe (deterioration only detected at very late stage)
The function of powertrain components is largely hidden from view. Reliability is achieved by a combination of hard time maintenance actions such as replacement, measurement, and overhaul at specified intervals. Powertrain reliability is not based on the principle of "run to failure". 1. in cauda venenum or "watch out for the part you can't see"
1. Aircraft Reciprocating-Engine Failure, An Analysis of Failure in Complex Engineered System. Australian Transport Safety Bureau, page 26.
Should an aircraft engine be operated past recommended TBO?
