Follow up on metal on oil screen

[Ted Waltman]

Here are questions that George Coy (at Gesoco) posed after I send him an
email, followed by a response from a knowledgeable individual on the
Pitts Model 12 list:

Questions (and my answers) posed by George:
------------
A couple of questions:

1. Is the material magnetic? Almost all was aluminum. Magnet picked up
very little.

2. Is the chip detector connected in the airplane and is it showing
anything? Yes--connected; No--not showing any light/alarm

3. How many hours of operation does this accumulation represent? 15.8
hours

4. It is hard to tell the volume of metal from your from your pix. I
agree; did the best light & conditions allowed. Amount of metal was,
though, much more than I've seen at previous cleanings. I did take off
the screen after flying it 1.2 hours after changing the oil. Some (very
little) metal present. I plan to take it off after 5, then 10 hours to
compare again.

Please back flush the screen onto a rag and gather it together. Will do
at next interval.

5. Are you doing any oil analysis? No. I plan to do so to create a
baseline at next oil change (within perhaps 8 more hours, or 10 hours
total)

6. Any other issues with the engine? No. Runs great.

------------

Info from Pitts list:
------------

I don't have any operating experience with the Vedeneyev engines yet.
But i do have with some other radial engines and a whole lot of
operation and overhaul experience with aircraft engines in general.

The radial engines I am familiar with, Jacobs, small P & W, small
Wrights have a tendency to thrust the master rod axially, usually
forward. This is not to be confused with the thrust load applied to the
front thrust bearing but is a result of natural twisting that occurrs
because of the different torsional loads applied to the mainshafts of
the cranks.

The result of this is wear to one piston pin plug more than the other,
depending on which way the master rod gets displaced and a small amount
of aluminum in the screen would be acceptable, the amouont decreasing in
time. A spectographic oil analysis is not likely to show this because
the pieces are too large ( even though they are small to the eye ), but
the aluminum content in the oil sample would be elevated slightly.

After a period of " bedding in " the visible particles should decrease,
almost down to nothing. Then as the engine approaches its service life,
the particle count would increase.

At some point, usually around 75 Hrs time in service or 75 hours after
major overhaul, the engine should become stable as far as particles in
the oil are concerned. I am going to make a judgement call here and say
that if the particles are no more than 1/4 a thimble. and are not
increasing, everything is most likely operating safely. This assumes
nothing is magnetic.

Any " flakes " or small pieces of non-ferrous material showing up in a
screen or in a paint filter as when changing the oil, would be cause for
investigation as there are very few points in an engine where aluminum
would be abraided but the most likely is a piston pin plug. That is why
some mechanics suggest close observation and they are reasonably
comfortable with a resample after another short operational period on
clean oil and clean screens. The screens do not keep these events from
happening, they only trap some of the stuff so that routine maintenance
will allow discovery of an impending failure. Also residual " trash "
from a previous failure is likely to show up for a while no matter how
thoroughly the oil system, particularly the cooler is cleaned.

Any " new " magnetic particles showing up after the initial 75 hrs or so
is reason to call off all bets. these require immediate attention and
no further airborn operation should,. in my opinion, be done until the
cause is positively identifed and corrected.

Most experienced engine people can look at the contamination with a high
powered jewelers loop, a microscope, and with the aid of a magnet, can
identify ball bearing material which becomes oil borne when a bearing
race is spalling and / brinnelling.

Most bearing races, even foreign ones will be made from 52100 steel or a
similar composition. If subjected to a metals lab for identification it
will be high in chrome.
Iron from piston rings, tappets, that sort of part will have a different
crystal structure which is visibly different from high alloy steel,
sometimes even to the un-aided eye.

Hope this helps.

Monty Barrett

Pitts 12 / 142





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