TM 1-1500-204-23-1
(8)
When there are no heavy metal particles in
engine, give engine a two hour flight test.
NOTE
When
engine
operated
properly
during flight test, examine oil system
for metal particles. If no metal is
found, continue engine in service,
but examine oil screens for presence
of metal after 10 hours of operation.
If no indication of internal failure is
found after 20 hours of operations,
engine requires no further special
examination.
d.
Metal Particles in Oil. Generally, metal particles
on engine oil screens or on magnetic sump plugs
indicate partial internal failure of the engine. However,
due to the construction of aircraft oil systems, it is
possible that metal particles may have collected in
sludge in the oil system at the time of previous engine
failure, consequently, this must be taken into account
when metal particles are found in engine oil screens or
on magnetic sump plugs. Frequently, carbon breaks
loose from the interior of the engine in large pieces
which
have
the
outward
appearance
of
metal.
However, carbon can be distinguished from metal by
placing the foreign material on a flat metal object and
hitting with a hammer. If material is carbon, it will
disintegrate when struck with a hammer, whereas metal
will either remain intact or change shape, depending
upon its malleability.
CAUTION
An oil soaked rag can very easily
cause
spontaneous
combustion
unless placed in a tightly closed
container, such as a quart or pint can
with a press-fit lid.
NOTE
Before
removing
an
engine
for
suspected
internal
failure,
as
Indicated by foreign matter on the oil
screens or oil sump plugs, collect all
obtainable
metal
particles
for
analysis and samples. To save fine
metal particles, it may be necessary
to strain the oil through a cloth. The
cloth and metal particles can be
placed in a clean metal container and
sent with engine for overhaul.
e.
Identification of Metal Particles. Metal particles
found in an engine may be of five kinds steel, tin,
aluminum, silver, and copper (or bronze). A visual
inspection as to color and hardness will occasionally be
sufficient to determine the kind of metal present. When
visual inspection does not positively identify the metal,
the kind of metal present may be determined by a few
simple tests performed with a permanent magnet,
electric soldering iron, or approximately 2 ounces of
hydrochloric acid and nitric acid as explained in the
following paragraphs.
WARNING
Exercise care in handling acid injury
or death to personnel may otherwise
result.
NOTE
The information in this paragraph is
not intended to be a substitute for,
nor release from the requirement for
compliance
with
the
Army
Oil
Analysis Program (AOAP) program
directed in accordance with TB 55-
6650-300-15.
(1)
Steel particle identification. Steel
particles can be Isolated by means of a permanent
magnet.
(2)
Tin particle Identification. Tin particles
can be identified by their low melting point. A soldering
iron should be cleaned, heated to approximately 260 °C
(500F), and thinned with 50-50 solder (50 percent lead
to 50 percent tin) Wipe off excess solder. A tin particle
dropped on heated Iron will melt and fuse with the
solder. Take care to avoid excessive overheating of
iron during this test.
(3)
Aluminum
particle
identification.
Aluminum particles may be identified by their respective
reaction with hydrochloric acid. When a particle of
aluminum is dropped into hydrochloric acid it will fizz
with a rapid emission of bubbles. The particle will
gradually disintegrate and form a black residue
(aluminum chloride).
(4)
Silver and copper particle identification.
Silver and copper (or bronze) may be identified by their
respective reactions in nitric acid. When a silver
particle is dropped into nitric acid, it will react rather
slowly, producing a whitish fog in the acid. When a
particle of copper (or bronze) is dropped into nitric acid it
will react rapidly, producing a bright green cloud in the
acid. There is no need in this instance to separate
copper from bronze.
7-25
