Posted for "Hamid A. Wasti" <hwasti@starband.net>:

           The following is a post from the Mooney list.  It is posted here
without permission for general knowledge.  While I do not agree with the
conclusion that oil analysis is useless, I do agree that if something looks
out of place, look into it proactively and not pull a Shannon.  The engine in
question is a Lycoming O-360.
 
 Hamid
 
 ####################
 
  The problem- A slightly rough left mag on the last flight and very fine
particles of aluminum (very small almost like dust also visible in sunlight
floating around in the oil) in every fold of the filter on the oil change due
after that last flight.. Not enough to qualify to tear down according to
Lycoming's service letters. Oil analysis AND microscope analysis said nothing
was wrong and aluminum content of oil was in "normal" parameters.    The
reason- Tore it down as it was more metal than I wanted to fly with
(especially at night over mountains here in the west) and when I removed the
rear case the left magneto drive gear and attaching parts fell off in my hand.
Seems the top bolt of the idler shaft hold down had either been stripped or
never tightened on previous assembly (or loosened up in the in the 1500 hrs of
engine time since overhaul) and it had wallowed out its hole along with the
idler shaft doing the same in its hole. The bottom bolt was still in its
threaded hole but it too had no threads on the bolt. The top bolt hole was
wallowed out to twice its diameter with no internal threads left.   I got
lucky and I caution anyone not to place too much faith in oil analysis. If it
seems like something is wrong it just might be.   64 M20 D/C