DRESSTA TD-25M EXTRA, Service Manual

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ELECTRICAL
SECTION 8
Page 43
DRESSTA TD-25M EXTRA
CRANKING MOTOR 42 MT
The solenoid windings are energized and the resulting plunger and shift lever movement causes
the pinion to engage the engine flywheel ring gear and the solenoid main contacts to close, and
cranking takes place. When the engine starts, pinion overrun protects the armature from excessive
speed until the switch is opened, at which time the return spring causes the pinion to disengage.
To prevent excessive overrun and damage to the drive and armature windings, the switch must be
opened immediately when the engine starts.
A cranking period for all types of motors should never exceed 30 seconds without stopping to allow
the motor to cool.
24. TROUBLESHOOTING THE CRANKING CIRCUIT
If the cranking system is not performing properly, make the following check to help determine
which part of the circuit is at fault.
a. Battery
To determine the condition of the battery, follow the testing procedure outlined in this Section,
BATTERY. Insure that the battery is fully charged.
The wiring, switches, and cranking motor
cannot be checked if the battery is defective or discharged.
b. Wiring
Inspect the wiring for damage. Inspect all connections to the cranking motor, solenoid, magnetic
switch, any other control switch, and battery, including all ground connections. Clean and tighten
all connections as required.
The cranking system cannot operate properly with excessive resistance in the circuit.
c. Magnetic Switch, Solenoid and Control Switches
Inspect all switches to determine their condition. From the Electrical Dozer System determine
which circuits should be energized with the starting switches closed. Use a voltmeter to detect any
open circuits.
d. Motor
If the battery, wiring and switches are in satisfactory condition, and the engine is known to be
functioning properly, remove the motor and follow the test procedures outlined below.
A cranking motor is designed for intermittent duty only, and should never be operated for more
than 30 seconds at a time. After 30 seconds, the cranking must be stopped for at least two minutes
to allow the motor to cool.
With the cranking motor removed from the engine, the armature should be checked for freedom of
rotation by prying the pinion with a screwdriver. Tight bearings, a bent armature shaft, or a loose
pole shoe screw will cause the armature does not turn freely. If the armature does not turn freely
the motor should be disassembled immediately. However, if the armature does rotate freely, the
motor should be given a no-load test before disassembly.