Starting Motor Inspection: Armature

Check commutator for dirt or burn. Correct commutator with sandpaper or lathe if necessary.

Fig 1: Checking Commutator For Dirt Or Burn
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Check commutator for uneven wear with armature (1) supported on V-blocks (2) by using dial gauge (4). If dial gauge (4) deflection exceeds the limit, repair commutator or replace armature.
Commutator out of round

Standard: 0.05 mm (0.002 in.) or less

Limit: 0.4 mm (0.02 in.)

Fig 2: Checking Commutator For Uneven Wear With Armature On V-Blocks By Using Dial Gauge
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Check commutator for wear and measure diameter of commutator. If diameter of commutator is lower than the limit, replace armature.
Commutator outside diameter

Standard: 29.4 mm (1.16 in.)

Limit: 28.8 mm (1.13 in.)

Fig 3: Checking Commutator For Wear And Measure Diameter Of Commutator
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Check commutator (1) for insulator (2) depth. Correct insulator depth if it is lower than the limit.
Commutator insulator depth "a"

Standard: 0.5 mm (0.020 in)

Limit: 0.2 mm (0.008 in.)

Fig 4: Checking Commutator Insulator Depth
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Check insulation between commutator and armature core. If there is continuity, replace armature.

Fig 5: Checking Insulation Between Commutator And Armature Core
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Check for continuity between segments. If there is no continuity at any test point, replace armature

Fig 6: Checking Continuity Between Segments
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