50-50 solder (50-percent tin and 50-percent lead).
plugs indicating (A) engine bearing failure and (B)
A tin particle dropped on the soldering iron will
normal buildup of fuzz.
melt and fuse with the solder.
NOTE: Fuzz consists of fine, hairlike
3. Aluminum (Al). Aluminum particles can
be determined by their reaction with hydrochloric
particles resulting from normal wear. Fuzz
accumulation may be more noticeable on
acid. When a particle of aluminum is dropped into
new engines during the first. 100 hours of
the hydrochloric (muriatic) acid, it will fizz, and
operation. Always refer to your specific
the particle will gradually disintegrate. Aluminum
aircraft and engine MIM for contamina-
particles will also dissolve rapidly and form a
white cloud in a strong caustic solution (sodium
tion and serviceability limits. Rejection
criteria for one engine may be only an oil
or potassium hydroxide). Silver and copper
flush and oil component replacement on
(bronze) do not noticeably react with hydrochloric
another type engine.
acid.
4. Silver (Ag) and copper (Cu). Silver and
METAL PARTICLE IDENTIFICATION
copper (bronze because of its high copper
contents) may be differentiated by their respective
reactions in nitric acid. When a silver particle is
Metal particles found on the oil strainer
screens and mag plugs indicate a possible failed
dropped into nitric acid, it will react with the acid,
slowly producing a whitish fog in the acid. When
part or impending engine failure. The presence
a particle of copper (bronze) is dropped into the
of metal particles on the oil screen or on the mag
nitric acid, it will react rapidly with the acid. This
plug does not mean that the engine must be
replaced. The type (steel, bronze), shape (flakes,
reaction produces a bright, bluish-green cloud in
chunks), and quantity determine the source and
the acid.
5. Chromium (Cr). These particles may be
dictate whether or not an engine is serviceable.
The metals usually found are steel, tin, aluminum,
determined by their reaction to hydrochloric acid.
When a chromium particle is dropped into
silver, copper (bronze), chromium, nickel, and tin
concentrated hydrochloric acid, the acid will
cadmium combinations. With some experience
you can make a visual inspection as to color and
develop a greenish cloud.
hardness, and it will help you to identify the metal
6. Cadmium (Cd). Cadmium particles will
dissolve rapidly when dropped into a 5-percent
particles. The particles of metal found in an engine
may be a granular, flake, or chunk.
solution of chromic acid.
When a visual inspection does not positively
7. Tin cadmium. These particles will dissolve
rapidly when dropped into a 5-percent solution
identify the metal, the kind of metal may be
of chromic acid. The tin content will cause a
determined by a few simple tests. These tests are
clouding of the solution.
performed with a permanent magnet and an
electric soldering iron. You also need about
2 ounces each of concentrated hydrochloric
Make sure the metal particles found in the oil
(muriatic) acid, concentrated nitric acid, chromic
are of an acceptable quantity for the engine to
acid, and sodium or potassium hydroxide.
remain in service. Always refer to the applicable
maintenance instruction manual for the limits of
metal particles for each particular engine.
CAUTION
NAVY OIL ANALYSIS PROGRAM
(NOAP)
Always use the appropriate protective
clothing and equipment, and use extreme
The Navy Oil Analysis Program (NOAP)
care when handling acids.
provides a diagnostic technique to monitor and
diagnose equipment or oil condition. This is done
The following test procedures help determine
without the removal or extensive disassembly of
different types of metal particles:
the equipment. It is mandatory for all activities
1. Iron (Fe) and nickel (Ni). Use a permanent
operating aeronautical equipment to participate
in this program. Type commanders or the
magnet to isolate these metal particles.
cognizant field activity (CFA) are the only ones
2. Tin (Sn). Tin particles can be distinguished
to relieve you from this requirement. The CFA
by their low melting point. Use a clean soldering
provides information on the sampling points,
iron, heated to 500F (250C) and tinned with a
5-21
