the armature shaft and slide on the drive head assembly (18) over the key. Install the drive spring (23) over the drive
head. Place the driving shaft assembly (22) in its position inside the drive spring, and mated with the drive head. Use new
locking clips (19), and install the head spring screw (20) in the drive head and the shaft spring screw (21) in the driving
shaft assembly. Insert the armature into the drive housing (28) until the shaft mates with the drive-end bushing (27).
Install the oil wick (26) and pipe plug (25). Fasten the center bearing to the drive housing with the screws (10) and
lockwashers (11). Place the commutator-end spacer washer (1) on the shaft next to the commutator. Place the field frame
followed by the commutator-end frame (36) into position. Lift the brushes as the commutator is brought into position.
Fasten the assembly with the through-bolts (39) and lockwashers (38). Install the commutator-end plug (37). Fasten the
field coil leads to the brush holders. Install the cover band (29).
f. Testing.
(1) No-load test. Connect the starting motor in series with a freshly charged 24-volt battery and an ammeter
with a 0-50 ampere range. At no-load the starting motor should draw 30 amperes and run at 6,000 rpm.
Read the motor speed with a tachometer. If the speed or current drain is not as specified, check the
brushes, commutator, field coils, and bearings as in d above.
(2) Torque test. Torque testing equipment is required for conducting a stall torque test on the starting motor.
With the motor connected in series with a freshly charged 24-volt battery, an ammeter with a 0-300 ampere
range, and a voltmeter connected across the motor terminals, run the stall torque test. When the motor
stalls, the current should be 200 amperes, the voltage 6.6 volts, with a torque of 21 ft-lbs. If the motor fails
this test, check the brushes, commutator, field coils, and bearings as in d above.
g. Installation. Refer to paragraph 93b.
199. Magnetic Switch
a. Description. The 24-volt magnetic switch is used with the starting switch in the starting circuit to close the circuit
between the batteries and starting motor. It consists essentially of a coil, plunger, contact disk, a terminal cap assembly
and return spring. When the coil is engaged through the starting switch, the plunger moves the contact disk to make
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