PAN-OIL FRONT 9M8897 - Caterpillar

Illustration 1 g03653705
Typical 24 V Starting Circuit (1) Test Point (2) Test Point (3) Test Point (4) Test Point (5) Test Point (X) Hold-in Coil (W) Pull-in CoilThe following troubleshooting procedures are intended to help the technician find the cause of the starting motor problem. The procedures are not intended to cover all possible problems and conditions. A common 24 V circuit is shown. If the troubleshooting procedures do not determine the cause of the malfunction, use Testing and Adjusting, "No Load - Test".All starting systems are made up of four elements:
Start switch
Start relay
Starting motor solenoid
Starting motorStart switches are relatively low current devices. These switches are rated for 5 to 20 A. Because the coil of a start relay draws about 1 A, the start switch can easily turn on the start relay. The coil of a start relay is between test points (1) and (2) on Illustration 1.The switch contacts of a typical start relay are rated for 100 to 300 A. Because a starter solenoid requires 5 to 50 A, the start relay can easily switch this load.The starting motor solenoid is a high current switch that is rated at about 1000 A. The starting motor solenoid engages the pinion with the flywheel and turns on the starting motor. The starting motor solenoid has two coils:
Pull-in coil (W)
Hold-in coil (X) The pull-in coil (W) draws about 40 A. The hold-in coil (X) requires about 5 A. When the start relay closes, both coils receive power. Battery voltage is applied to the high end of both coils at test point (3) which is the start terminal (S). The low end of the hold-in coil is permanently grounded to the ground post of the starting motor. Grounding for the low end of the pull-in coil (test point (4) ) is momentary. Grounding takes place through the DC resistance of the starting motor. When the magnetic force builds up in both coils, the pinion moves toward the flywheel ring gear. During this period, the pull-in coil is out of the circuit. Cranking continues until the start switch is released.These switches and relays permit a 5 Amp dash-mounted switch to turn on a 500 to 1000 A motor that is used to crank an engine.The M105R starter motor has a special function-soft engagement. When the M105 starter is energized, the pinion moves forward under operation of the solenoid and lever. If the pinion does not engage directly into ring-gear, the tooth to tooth phenomenon occurs. The solenoid contacts cannot close, causing the current from the battery terminal to pass through the "Pull-in Coil" and "Hold-in Coil" of the solenoid. Because the current branch passes through the "Pull-in Coil", a current of approximately 200 A to 300 A is induced into the motor. The current flows as follows: Starter B+ to the contacts, to the pull-in coil, to the motor part, to the earth. The starter makes a soft engaged torque of approximately 15 Nm, causing the pinion to rotate slowly and