WRENCH A- 6V4074 - Caterpillar

Table 1
Tools Needed    
6V-7070     Digital Multimeter    
225-8266     Ammeter Tool Gp    
1U-6602     Photo-Tachometer    The following procedure is used in order to perform the no-load test after the starting motor has been repaired. The 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. To check the starting motor components, refer to the Testing and Adjusting section.
Illustration 1 g02718921
No load test diagram (24V)
Illustration 1 shows a 24 V system with two 12 V batteries that are connected in series to a starting motor. Connect one 12 V battery for a 12 V system. Connect the positive side of the battery cable to the "BAT" terminal of the starting motor solenoid. Connect the negative side of the battery cable to the negative terminal of the starting motor.
As shown, connect an open switch between the "S" terminal and the "BAT" terminal of the solenoid.
Connect the multimeter red lead to the "Mtr" terminal on the solenoid. Connect the multimeter black lead to the negative terminal of the starting motor.
Use a phototach or a rpm indicator in order to measure the speed of the armature.
Close the switch. The measurements in Table 2 should be observed:
Table 2
No Load Test     37-MT
12 V     37-MT
24 V     41-MT
12 V     41-MT
24 V     42-MT
12 V     42-MT
24 V    
Minimum Voltage     11 V     23 V     11 V     23 V     11 V     23 V    
Minimum Speed     5501 rpm     3215 rpm     5501 rpm     7200 rpm     5100 rpm     5960 rpm    
Maximum Speed     8535 rpm     4041 rpm     8535 rpm     9700 rpm     8700 rpm     9326 rpm    
Minimum Current Draw     100 Amp     68 Amp     100 Amp     68 Amp     100 Amp     68 Amp    
Maximum Current Draw     155 Amp     100 Amp     155 Amp     100 Amp     155 Amp     100 Amp    
If the voltage is below the minimum, the batteries are low and the batteries need charged.Note: If the voltage is higher, the speed will be proportionally higher. No Load Test Results
The following information provides some results of a no-load test and the possible problems.
A rated current draw at a no-load speed indicates a normal starting motor.
A low free speed and a high current draw indicate:
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. A shorted armature can be checked on a growler tester after disassembly.
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