Starting Motor - Delco 50-MT Caterpillar

Armature Short Circuit - Test

Illustration 1	g00716053
Armature short circuit check (3) Armature assembly (A) Growler tester

1. Place armature (3) on growler tester (A). The tester needs to be turned to the ON position.

2. Hold a hacksaw blade against the armature core. Slowly rotate the armature while the blade is against the core.

3. The blade should not vibrate or the blade should not be attracted to the armature core.

4. If the blade vibrates or the blade is attracted to the core, the armature has a short. The armature must be rebuilt or replaced.

Armature Ground - Test

Illustration 2	g00716055
Armature winding ground test (3) Armature assembly

1. Place the multimeter in the "20M Ω" range. Touch one meter lead on each commutator bar and the other lead on the armature core.

2. Each multimeter reading should be greater than 100,000 Ohms. A meter reading of "0.10" or a value that is greater is acceptable.

3. If the meter reading is lower than 100,000 Ohms, the armature is grounded. The armature must be rebuilt or replaced.

Armature Continuity - Test

Special equipment is needed to test the armature for an open. If the commutator is pitted or the bars are burned, the armature has an open. The armature must be replaced.

Armature Runout - Check

Illustration 3	g00716057
Armature runout check (3) Armature assembly (4) Commutator (5) Core (B) Dial indicator

1. Check the runout "TIR" of the commutator (4) on the armature assembly (3). Check the "TIR" of the core (5) on the armature assembly (3). The maximum "TIR" that is allowed is 0.13 mm (0.005 inch).

2. If the "TIR" is too great, the armature must be replaced.

Commutator Outside Diameter - Check

Illustration 4	g00716059
Commutator outside diameter check (4) Commutator (C) Caliper

1. Use the caliper (C) to check the outside diameter of commutator (5). The new diameters of the commutator is 58.8 ± 0.10 mm (2.3150 ± 0.0040 inch). The minimum diameters of the commutator is 56.7 mm (2.230 inch).

2. If the armature is worn, the armature must be replaced.
   Show/hide table

   Illustration 5	g00584885
   Depth Of Segment Mica (X) Depth of segment mica

3. Measure the depth of segment mica of the commutator . The minimum depth should be 0.64 mm (0.025 inch).
   Show/hide table

   NOTICE
   Keep all parts clean from contaminants. Contaminants may cause rapid wear and shortened component life.

4. If the depth is under the minimum, the segment mica can be undercut. If the mica is undercut, remove all shavings and mica particles.