Component Testing: Armature

Test armature for shorted coils with a growler. Check for grounded coils with a 110 volt test lamp. Place one test lead on armature core or shaft, and other test lead on commutator. Lamp should not light. If lamp lights, armature is grounded and should be replaced.
Inspect commutator. If commutator is rough, worn or has protruding insulation, turn down commutator in a lathe. Do not turn to less than 1.650". Sand commutator lightly with commutator paper and clean out slots carefully.
CAUTION: Some starters have molded type commutator and insulation must not be undercut on these models (may cause serious damage to commutator).