4-9. GENERAL MAINTENANCE PROCEDURES- Continued
(4) Abrasive Wear. This damage is caused by fine particles carried in the lubricant or embedded in gear
tooth. This material may come from:
Bearing or gear tooth material.
Abrasives not removed during assembly.
Sand or scale from castings.
Impurities from oil or the environment.
(5) Scoring. Slight scoring, galling or other surface damage is seen as tears or scratches in the direction of
sliding. It starts in areas of highest stress and speed. This is usually at tip of teeth.
(6) Burning. Burning is seen as discoloration, and causes loss of hardness of the metal. Burning is caused by
any of the following:
Lack of Backlash
Too Little Lubrication
If discoloration can be wiped off, such marks can usually be traced to oil-burn stains which are not
(7) Rolling. This damage usually occurs only on plastic gears. Rolling is when material is pushed out of
shape but does not break off. It is usually caused by heavy, even loads and overheating.
h. Metal Parts. Visually inspect all castings and weldments for cracks. Parts that carry a great load should be
inspected by the magnetic particle method. Non-ferrous parts may be inspected by the fluorescent
Magnetic Particle Inspection. This type of inspection can only be carried out on metals that can be
magnetized. If in doubt check whether a magnet sticks to the surface. It should only be carried out it parts
are not easily replaceable (cost or special order), or parts have been reworked or reground, or parts are
subject to high stress. Magnetizing current depends on parts being magnetized. For solid section parts,
current shall be 1000 amps per diameter-inch. For variable diameter thickness, current shall be adjusted for
Parts shall be rejected if:
(1) Indications of non-metallic inclusions are present (foreign body-solid, liquid, or gaseous) and these are
longer than one inch, or indications are closer than 1/8 in. apart.
(2) Any evidence of cracks are seen.