My mechanic, checking on an oil leak, told me that my IO-360 has sagged a bit on the Lord mounts, letting the alternator rub on the right angle Airequip fitting that connects the oil line to the oil cooler. He’s ordered a new fitting and says he can correct the rubbing and oil leak. Everything was new 4 years and 300 hours ago when I installed a Lycoming factory overhauled engine. What’s happening?
All new rubber mounts take a “set” under load. So it’s not at all uncommon that several months after an engine is hung with new mounts that it needs to be re-shimmed. Washers are put between the engine crankcase and the rubber mount to shift the engine to line up with the cowl opening. Manufacturing tolerances for mounts and cowls are such that it’s not uncommon to need a shim or two just to center up the engine.
I prefer to deal with this pro-actively by shimming the engine (as evidenced by the location of the spinner with respect to the nose bowl opening) to be slightly high when first installed. By that I don’t mean that it’s obviously out of alignment, but rather, I put the tolerance of the shims on the high side, and this leaves the newly installed engine 3/16″-5/16″ higher than the centerline of the nose bowl hole.
Then a year or so later when I see the plane at annual, I might find that it’s sagged to be 1/4″ low. I’d investigate carefully how there was so much sag that the alternator pulley could contact the oil cooler line. There ought to have been way more clearance than the 1/2-3/4″ that the engine might have sagged.