Commutator Test

If commutator surface is dirty or burnt, it can be cleaned with No. 400 grit sandpaper or on a lathe.
Place the commutator on V-blocks and use a dial indicator to measure runout (out-of-round). See Fig 1. If commutator runout is more than specification, turn commutator on a lathe and proceed to step 3. For specification, see STARTER SPECIFICATIONS .
Measure commutator diameter. See Fig 2. If commutator diameter is less than minimum specification, see STARTER SPECIFICATIONS , replace armature.
Ensure undercut depth between commutator segments are clean, free of debris, and that edges are smooth, and within specification, see Fig 3. If undercut depth is less than minimum, use a hacksaw blade to correct it. See STARTER SPECIFICATIONS .

Fig 1: Measuring Commutator Runout

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Fig 2: Measuring Commutator Diameter

Fig 3: Measuring Undercut Depth