Parts Replacement & Testing: Armature

Check coil and commutator to shaft (or core) for short circuit, with 110 volt ac control lamp. Control lamp should not illuminate (slight illumination is possible due to dampness). Check coil to commutator for short circuit with a 6 volt DC control lamp, touching every coil on armature and its corresponding bar, brightness of lamp should not change. Check coils on armature for short circuit between windings using a growler.

Check out of round of commutator to core, it should not exceed 0.00197" (0.5 mm). Commutator should have a smooth greyish-blue surface with no grooves or burned spots otherwise, it must be turned. Minimum commutator diameter is 1.32" (33.5 mm). After turning commutator, undercut insulation to a depth of 0.0197 - 0.0236" (0.5 - 0.8 mm), decrease diameter by 0.0039" (0.1 mm). Do not use emery cloth, turn on a lathe only.