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Metals
Identification (oil filter examination )
Metals Identification of aircraft oil filters using field methods
Aluminum
Sodium hydroxide dissolves aluminum. Fizzes! Sodium hydroxide doesn't
react with steel, bronze, or tin. A good source for sodium hydroxide is Drano or
Red Devil drain cleaner (the powder kind). I prefer Red Devil since it is 100%
sodium hydroxide. If you mix some Drano in water and then place a drop on
aluminum the drop will sit there awhile while it works its way through the oil
film on the aluminum. As soon as it contacts aluminum it will start to fizz.
Since sodium hydroxide doesn't react with steel, bronze, chrome or tin it is an
excellent check for aluminum.
I have even used it on engine bearing and then watch through a microscope. If
the little embedded particles start to fizz then they are aluminum particles
embedded into the bearing.
Bronze or copper
Nitric acid. Reacts to form green liquid.
Chrome
Chrome is hard, brittle, and a plated material. Pieces of chrome are small,
flat with broken edges. Chrome is usually seen as many small shiny particles.
Hydrochloric acid reacts with chrome usually making the liquid green. Nitric
acid has no effect on chrome other than passivating the surface.
Glass Bead
Small round "fish egg" spheres when viewed under a magnifying
glass.
Hard Carbon
Breaks apart when squashed. Can be squashed between finger nails.
Inconel
No reaction in nitric acid.
Lead
Dissolves in nitric acid. These are often from leaded fuel and condense into
small glass-like gobbles (metallic lead) in the exhaust system. Lead crystals will squish
between your finger nails.
Plastic bead
Abrasive bead used to strip paint from airplanes. Some engine parts such as
crankcases.
Several types with differing appearance. Can have a white frosted appearance.
Colored plastic is fractured with smooth bright surfaces. Will not scratch
glass.
Lead crystals from
leaded fuel
Glass like (may be mistaken for glass bead). Dissolves in water. Usually
found in exhaust port of cylinder on engines operating on leaded fuel.
Magnesium
25% Hydrochloric acid in water. Fizzes immediately on contact and forms a
black deposit. Zinc reacts in same manner. Aluminum also reacts with
concentrated hydrochloric acid by fizzing slightly and leaving a dark surface.
25% Nitric acid turns magnesium black.
Minerals
Small colored crystals with fractured surfaces. If found in engine, check the
induction system carefully in the crooks and crannies. If found in the induction
system then source of minerals was thru ingestion.
Monel
Nitric acid turns metal blue-green. Steel rod rubbed in solution will turn
copper colored. Monel is a alloy of copper and nickel.
Silica (sand)
Place between glass slides and rub together. Silica scratches the glass.
Silver
Nitric acid. Slowly reacts to form whitish silver nitrate fog in acid.
Steel
Copper sulfate dissolved in dilute sulfuric acid. Turns steel copper color.
Nitric acid in various concentrations etches steel. The higher the concentration
of nitric acid the darker the reaction etch. Nitrided steel surfaces react very
slowly.
Tin
Heat knife to red hot. Place against particle. Tin will melt.
Hydrochloric acid immediately causes tin particles to fizz. Pieces of tin
will float to the top of the bubble.
Nitric acid causes tin to turn slightly dark with some bubbles attached.
Hydrochloric acid turns tin into stannous chloride and hydrogen gas.
Will not be attracted to a magnet.
Wire
Measure diameter. Small diameter wire may be from hoses. Wire with one
fractured end and one rounded end is from wire wheel. Likely source is bits of
safety wire left on workbench that find their way into engines.
Aircraft Oil Filter Media Condition
One inspection item that is often overlooked when
inspecting the oil filter is inspecting the condition of the filter paper. As
the filter media ages or is exposed to excessively hot temperatures it gets dark
and brittle. Normal filter media should retain it's light yellow/tan color and
not break apart when bent.
Non-turbocharged: Tan/yellow colored, small amounts of
hard carbon. Filter paper should not be brittle. Dark filter media without
significant hard carbon means the filter has not been changed often enough. Dark
filter media with significant amounts of hard carbon indicate high oil
temperatures. Suspect compression blow-by, or poor engine baffle.
Turbocharged: Tan/yellow to dark colored with
more amounts of hard carbon. If filter media is brittle then filter should be
changed more often or oil temperatures should be reduced.
Aircraft
Oil Filter Morphology
Chunks
Dents and deformation indicate secondary damage has occurred when chunks wedged
and jammed between moving engine. Evidence of fatigue markings indicates chunk
originated from a primary failure point. Brittle fracture indicates impact
failure from some other failed part.
Melted
Melted aluminum globules indicate preignition or detonation damage. Source is
usually the piston.
Slivers
Small flat slivers are most likely tin or chrome. Probable tin source is
washers. Particularly on Continental engines the rocker arm thrust washer is
suspect; usually not cause for concern. Cut and gouged slivers indicate metal on
metal gouging. Source should be identified. Large amounts of bronze slivers in
continental engines is most likely from starter adapter gear. Continental engine
IO-520AE doesn't use a bronze starter adapter gear.
Platelets
Flat round steel slivers with possibly small cracks at the edges are from roller
fatigue. Most possible source is camshaft lobes and camshaft followers. Chrome
flaking off of chrome plated cylinders is another source for platelets. Bearing
Babbitt flaking off the bearings will create platelets.
Machine marks:
Machine marks gives clues to the possible source.
Carbon deposits:
Carbon or varnish deposits indicate the source was in a high temperature zone.
Metallic:
Very small metallic particles found in the oil are best seen in bright
sunlight. Take a oil sample out into the sunlight. Any small metallic particles
such as microscopic particles of brass will reflect sunlight. Indoors the same
particles may be invisible.
If this doesn't work--I'm going over the side. Parachute
Sense US NAVY 1944
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