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Hi all,
While working on our Mooney M10 (1970), the mechanic found a oil leak in
one
of the cylinder (Continental C90 Series). The lower plug was filled with
oil
and oil was slowly dripping from the cylinder. The oil leak has been there
for
the last 2 years at least but was judged non-significant at that time.
Iridium
plugs were installed to compensate for that problem. Now, the leak seems
to be
a bit more significant and I was told by the mechanic that the rings might
have rotated and some gaps aligned. He expressed his concern that this
might
lead to detonations and fire.
Now, the engine had top overhaul in 1998, after 783 hours. Today, the
engine
has about 960 hours. Regular chemical analysis of oil is excellent. The
compression numbers are good however the mechanic has observed that
they do slowly increase (from 75psi to 78psi) over the last 2 years while
they
would normally decrease because of wear (NOTE: I do not understand what
those
values correspond to. It seems to be a test in which pressure is set on
one
side of the cylinder and a different pressure is measured in some other
place?). Oil consumption seems to be roughly stable over the last year and
with comparable values to what is observed in other Ercoupe. The mechanic
however claim we are seeing a slight increase. Finally, the mechanic
observed
some drops of 150rpm during magneto checks which the previous owner and my
current co-owner do not observe. I was told that it might be because the
mag
checks were done after the engine ran long enough to splash or burn off
the
oil on the bottom plug.
I'm completely ignorant in the field but I believe the above is a factual
report of the situation and I would be interested in hearing from the
mechanics or any other knowledgeable person on the list on the matter of:
(1) the need or not for repair
(2) the actual risks of detonations and fire.
One more question: if a mechanic really believes that there are risks of
detonations and fire in an engine, can he sign off the airplane at annual
inspection? or is he legally or ethically bound to ground the airplane?
Thank you for your help,
Luc Berthouze
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