(Les Sullivan) wrote:
I have a 1972 Cessna 172 with a Lycoming 0-320-E2D engine and it runs
beautifully. It is on UK private category.
The engine is "original" and total time is about 2800 hours.
The engine had a thorough top overhaul quite a few years ago, maybe
around 1500 hours (new pistons etc) and has no problems with
compression, oil consumption, vibration or indeed anything at all. It
is well looked after.
Now the but.....
At its last annual (Christmas) some metal particles were found in the
oil filter.

I agree with your conclusion, which is that the engine has no life left
in it. If I understand properly, the engine left the factory 32 years
and 2800 hours ago and has never been overhauled except to change
cylinders? You're way beyond TBO by both calendar and hour limits.

I don't know how the regs work in the UK, but I assume they're the same
as here, in as much as TBO is not regulatory for private operations.
Still, the metal doesn't know what country it's registered in. I'm not
terribly concerned about running an engine past TBO, but if you're got
2800 hours in 32 years, that's averaging less than 100 hours a year,
which raises a warning flag in my mind about internal rust and
corrision. Now that you're producing metal chips, I think your best bet
is to be happy that you got your money's worth and more out of the
original engine.

a) Factory Zero timed engine
b) Factory overhauled engine
c) Have my own engine worked on

What are your views about which way to go with this?

My pesonal opinion is that a Factory zero time engine is the way to go.
It is also the most expensive of the alternatives you listed. I cannot
offer any cohesive argument to back up my suggestion, it's just my
personal opinion. I'm sure other people will give you other (equally
valid) opinions.

It is awfully tempting to keep the plane running and cut open the new
oil filter at, say, 20hours and see if there are any more particles.
As I said, compressions, oil pressure, power etc. are all good.

For what it's worth, when my club had an engine that started producing
metal in the oil filter, we did exactly that (although I think we did it
at 10 hours). We got more metal. We were told (by Mattituck) that
given the type of metal and the shape of the particles, source had to be
wrist pins rubbing on the cylinder walls. Encouraged by the thought
that we might get out of this with just a top overhaul, we had all 4
cylinders pulled. There was no visible damage to any of the wrist pins
or cylinder walls. We had the oil pump pulled, and again there was no
visible damage there.

In our case, we had a bit of a dilema, because the engine was much newer
(about 1300 SMOH) so there was a lot of value left in it and we were
very much interested in avoiding having to overhaul or replace it if
possible. With 32 years and 2800 hours on yours, you should have no
such thoughts. What we ended up doing was wasting a lot of money and
time doing diagnostic work that ended up for naught. It's a crapshoot.
Ultimately, we replaced the engine.

Maybe my greatest fear is that if I keep it flying, there may be
damage caused to the crankshaft or something which causes a big price
increase at overhaul due to the part being rejected.

My fear would be that you're chewing up some critical bearing and you'll
have a catastrophic engine failure in flight. A reputable engine shop
should be able to look at the metal chips and give you a good guess
where they're coming from. But, again, with the age of your engine, any
further diagnostic work is really somewhat of an academic exercise.