SPRING 9N5077 - 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 completely check a starting motor, the complete procedure should be followed. The complete procedure is shown in the Initial Troubleshooting Procedure. To check the starting motor components, see Testing and Adjusting.
Illustration 1 g00719284
No load test diagram
As shown, connect a fully charged battery at system voltage to the starting motor. Connect the + battery cable to the battery terminal on the solenoid. Connect the negative battery cable to the starting motor negative terminal.
As shown, connect an open switch between the "S" terminal and the "Bat" terminal of the solenoid.
Connect the multimeter red lead to the solenoid Mtr terminal. Connect the black lead to the starting motor negative housing.
Use a Photo-Tachometer in order to measure the speed of the armature.
Close the switch. At 10.5 Volts, the minimum speed must be 7800 rpm. The maximum current draw is 170 amp.
If the voltage is below 10.5 Volts, the batteries are low and the batteries need to be 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.
Achieving the rated current draw at a no load speed condition indicates a normal starting motor.
A low free speed and a high current draw indicates:
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.
A shorted armature could cause a high current draw. Disassemble the starting motor. Check the armature on a growler tester.
A grounded armature or a grounded field winding could cause a high current draw. Check for grounds after disassembly.
Failure to operate with a high current draw indicates:
A direct ground in the terminal or field windings.
The bearings cease to operate properly. This can be seen by turning the armature by hand.
Failure to operate with no current draw indicates:
An open field circuit will cause a failure. The system can be checked for an open field circuit with a multimeter after disassembly.
An open armature will cause a failure. Inspect the commutator for badly burned bars.
Broken brush springs, worn brushes or high insulation between the commutator bars could prevent good contact between the brushes and the commutator.
A low no load speed and a low current draw indicates:
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.
A high free speed and a high current draw indicates:
A shorted field circuit will cause a failure. Check the field winding for shorts after disassembly.