The best quote yet from Jim Doebler – "These engines will whisper before they scream." In other words, listen carefully to what your engine is telling you – problems caught early are much easier to fix.
An engine came back for overhaul at 2,000 hours, and the technician called in the field reps to observe the great care with which the owner had maintained it. He took such great care that he had even applied factory paint to the safety wire securing the suction screen... (those suction screens are supposed to be removed and cleaned at every oil change).
Given accurate instrumentation that doesn’t drift over the life of an engine (not an easy thing to ensure), cruise oil pressure shouldn’t change more than 1 psi over the TBO life of the engine. If it does, something has gone wrong.
All new Lycoming employees – from engineers to secretaries – are sent to the Service Class to ensure that they have a background in what the company does.
For those with the old cylindrical oil screens instead of a replaceable filter, the screen itself has a soldered seam that is designed to rupture if the screen itself becomes clogged, thereby providing a relief capability to keep oil flowing through the engine. Dirty oil is better than no oil.
And finally, the particulate “rule of thumb” – if you clean the filter and screen and produce enough metal to cover an area larger than your thumbnail – you have a problem. Less than that, you can button things up and run it some more. Doebler was not specific as to whose thumbnail however.