Parts Replacement & Testing: Commutator
Clean commutator with a cloth moistened in gasoline and if this is not effective, carefully polish with a strip of fine glass paper while rotating armature. To correct a badly worn commutator, disassemble starter as previously described and remove armature from end bracket. Mount armature in a lathe and rotate at high speed, taking a light cut on commutator with a very sharp tool. Do not remove more metal than is absolutely necessary.
NOTE:
Insulators, between commutator segments, must not be undercut.