Parts Replacement & Testing: Armature

Check coil and commutator to shaft (or core) for short circuit, with 110 volt AC; 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" (0.1mm), do not use emery cloth, but turn on a lathe.