RA1.2, R1.4, R2.0, R2.2, R2.5, R2.7, R3.0, R4.5 and R5.5 Series Reduction Starting Motors Caterpillar

The following procedure is used in order to perform a no load test after the starting motor has been repaired. The no load test should also be performed when the starting motor is removed from the machine. In order to check a starting motor completely, the complete procedure should be followed. The complete procedure is shown in the Initial Troubleshooting Procedure. To check the starting motor components, see Starting Motor Component Tests.

Illustration 1	g00584747
No Load Test Diagram (24 V Shown).

1. The above illustration shows two batteries (12 V) that are connected to a starting motor. Use one battery for a 12 V system. Connect the positive battery cable to the Battery terminal of the starting motor solenoid. Connect the negative battery cable to the starting motor negative terminal.

2. As shown, connect an open switch between the S terminal and the BAT terminal of the solenoid.

3. Connect the multimeter red lead to the solenoid motor terminal. Connect the black lead to the starting motor negative terminal.

4. Use an rpm indicator or photo tachometer in order to measure the speed of the armature.

5. Close the switch. The specifications section provides the table for the maximum current draw. The specification section also provides the table for minimum voltages.

6. If the voltage is below the minimum, the batteries are low and the batteries needs charged. If the voltage is higher, the speed will be proportionally higher.

Possible No Load Test Results

The following information provides some no load test results that could be seen and corresponding possible problems.

1. Achieving the rated current draw at a no load speed condition indicates a normal starting motor.

2. A low free speed and a high current draw indicate:

   1. An increase in friction could be caused by tight bearings, dirty bearings, or worn bearings. A bent armature or loose field pole shoes that would allow the armature to drag are possible causes of increased friction.

   2. A shorted armature could cause a high current draw. A shorted armature can be further checked on a growler after disassembly.

   3. A grounded armature or a grounded field winding could cause a high current draw. Check for grounds after disassembly.

3. Failure to operate with a high current draw indicates:

   1. A direct ground in the terminal or field windings.

   2. The bearings cease to operate properly. This can be seen by turning the armature by hand.

4. Failure to operate with no current draw indicates:

   1. An open field circuit will cause a failure. The system can be checked for an open field circuit with a multimeter after disassembly.

   2. An open armature will cause a failure. Inspect the commutator for badly burned bars.

   3. Broken brush springs, worn brushes, or high insulation between the commutator bars could prevent good contact between the brushes and the commutator.

5. A low no load speed and a low current draw indicate:

   1. An internal resistance that is high is possibly caused by poor connections, leads that are faulty, a commutator that is dirty, and/or causes that are listed in 4.

6. A high free speed and a high current draw indicate:

   1. A shorted field circuit will cause a failure. Check the field winding for shorts after disassembly.