Case 550H Crawler Dozer Repair Manual

Manuals: Service Manual

General

Engines

Fuel System

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Manual Extract Understanding No Load Test Results

1. If the current draw and the armature shaft speed are within the ranges under Specifications, the starter is good.

2. Low armature shaft speed and high current draw are indications of too much friction. Possible causes of too much friction are: A. Tight, dirty, or worn bearings.

B. A bent armature shaft.

C. Loose pole shoes (pole shoes make contact with the armature).

D. A short circuit in the armature coil.

Disassemble the starter. Use an armature tester to test the armature. Use the instructions included with the armature tester.

E. Damaged field coil. Do the test on Page 4006-12.

3. If the armature does not rotate and the current draw is high, possible causes are: A. Field terminal making contact with the field frame. Inspect the insulators for the field terminal.

B. Damaged field coil. Do the tests on Page 4006-13.

C. Damaged bearings.

4. If the armature does not rotate and the current draw is zero, possible causes are: A. An open field circuit. Disassemble the starter and inspect the field coil connections.

B. An open armature coil. Disassemble the starter and check for burned commutator bars.

Use an armature tester to test the armature.

Use the instructions included with the armature tester.

C. Brushes not making good contact with the commutator bars. Check for high insulation between the commutator bars, broken brush springs, or worn brushes.

5. Low armature shaft speed and low current draw are indications of:

A. Dirt or corrosion on connections.

B. Damaged wiring.

C. Dirty commutator bars.

D. All causes in Step 4.

6. High armature shaft speed and high current draw are indications of a short circuit in the field coil. It is difficult to find a short circuit in a field coil.

Install a new field coil. Do the No Load Test again to check for improvement in the operation of the starter.