Wear-Metal Sources.

NAVAIR 17-15-50.4

TM 38-301-4

T.O. 33-1-37-4

CGTO 33-1-37-4

b. Transmissions are difficult to evaluate and may be relatively easily contaminated with dirt, sand, and

water. Transmissions may reveal high increases in debris (both metals and nonmetals) without detrimental wear

of the oil-wetted working components. Therefore, the evaluator should be familiar with the transmissions being

evaluated and also with any factors that might cause extreme or sudden increases in transmission oil

c. The specific metals that may normally be found in diesel engines and transmissions of nonaeronautical

equipment used by the military services are discussed below:

(1) Iron (Fe). Iron is one of the most common wear-metals found in oil samples. Iron may be

generated from the wear of cylinder walls, shafts, gears, rolling element bearings, splines, and numerous other

engine or transmission parts. Iron may also be the result of machining chips or debris left in the equipment oil

system during manufacture or overhaul. Iron may also be present as a result of rust in some equipment.

(2) Silver (Ag). Silver is used as plating on some oil seals and bushings and may also be found in

small amounts in some sleeve bushings.

(3) Aluminum (Al). Aluminum may be found in the oil systems of engines and transmissions because

of the wear of pistons, washers, shims, some oil pumps, torque convectors, housings or cases, etc. It may also

be the result of machining chips or debris left in the equipment oil system during manufacture or overhaul.

(4) Chromium (Cr). Chromium in the oil system may result from the wear of numerous oil-wetted

parts that are alloyed or plated with chromium. The most common occurrence will probably result from wear of

chromium plated piston rings.

(5) Copper (Cu). Copper is found in connecting rod and main bearings, many bushings, thrust

washers and piston pin bearings.; Also, many transmission and brake plates contain sintered bronze, which is

very high in copper content.

(6) Silicon (Si). Although not a metallic element, silicon is commonly present in many oil systems and

may be detected by spectrometric testing. The main source of silicon in engines (silica) is from external sources

through the air induction system, which may admit significant amounts of dirt or sand if not maintained properly.

Silicon may also be introduced in the form of dirt or sand during maintenance if proper maintenance practices are

not observed. Aluminum and cast iron parts used in both engines and transmissions have significant amount of

silicon. Some seals and gaskets, as well as antifoaming agents in oils, also contain silicon and/or silicone.

(7) Tin (Sn). Tin is used to plate some engine pistons and may also be present in connecting rod and

main bearings, many bushings, thrust washers and piston pin bearings.

(8) Nickel (Ni). Nickel is used for plating and as an alloying element in many oil-wetted components.

Some cast irons and stainless steels contain significant amounts of nickel.

(9) Lead (Pb). Lead is used for plating and may be found in significant amounts in connecting rod

and main bearings, bushings, thrust washers and piston pin bearings. Lead may also be found in transmission

clutch and brake friction plates.

(10) Molybdenum (Mo). Molybdenum is used as an alloying element in many oil-wetted engine and

transmission components. Molybdenum is also used as a coating on the top, second, and third compression rings

in the Continental AVDS 1790 engines and on the top ring of the Caterpillar 3208 engines.

(11) Magnesium (Mg). Magnesium is used as an alloying element in some oil-wetted components but

is not employed extensively for nonaeronautical vehicles where weight is a less significant factor.

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