llustration 1 g00709948
Starting motor components
(1) Rear frame assembly
(2) Solenoid assembly
(3) Plunger assembly
(4) Shift lever housing
(5) Shift lever assembly
(6) Pinion drive housing
(7) Pinion drive assembly
(8) Brushes
(9) Brush plate assembly
(10) Pole shoes
(11) Field winding assembly
(12) Armature assembly
(13) Starting motor housing
The major components of the 50-MT series starting motor are the following items:
•Starting motor housing (13)
•Field winding assembly (11)
•Pole shoes (10)
•Armature assembly (12)
•Brushes (8)
•Brush plate assembly (9)
•Pinion drive assembly (7)
•Shift lever assembly (5)
•Plunger assembly (3)
•Solenoid assembly (2)
•Rear frame assembly (1)
Illustration 2 g00710078
Starting motor housing
(10) Pole shoes
(11) Field winding assembly
(13) Starting motor housing
The starter motor housing (13) supports the following items: field winding assembly (11), pole shoes (10), brush plate assembly (9) and brushes (8) .
The field winding (11) and the pole shoes (10) provides the magnetic field for the armature assembly (12).
Illustration 3 g00710311
Armature assembly
(12) Armature assembly
The armature assembly (12) consists of a laminated iron core which is assembled on the armature shaft. The commutator is at one end of the armature. The commutator is constructed of copper bars. The bars are insulated from each other and the armature shaft. The armature windings are wound in the slots of the core. The windings are then connected to the commutator segments.
The armature assembly (12) is positioned in the field winding assembly (11) and the pole shoes (10). The armature assembly is supported by bearings which are located in the following components: pinion drive housing, shift lever housing and rear frame assembly.
The armature assembly and the field winding are connected in series. The current flow generates high torque especially when the motor is first started
Illustration 4 g00710338
Brush holder assembly
(9) Brush plate assembly
(14) Brush springs
The brush holder assembly (9) is mounted over the commutator to the case of the starting motor housing. Six brushes are held against the commutator. Brush springs (14) keep pressure on the brushes so the brushes stay in contact with the commutator. The brushes transmit current from the field winding to the commutator. Three of the brushes are positive polarity and these brushes are connected to the field winding. The other three brushes are negative polarity and these brushes are connected to the negative terminal of the starting motor.
Illustration 5 g00710518
Brushes
(8) Brush
Brushes (8) are constructed of carbon. The carbon is used to conduct electricity. The brushes transmit current from the field winding to the commutator. There are six brushes. Three of the brushes are positive and three of the brushes are negative.
Illustration 6 g00710702
Pinion drive assembly
(7) Pinion drive assembly
(15) Pinion gear
The pinion drive assembly (7) has a pinion gear (15) that will engage onto the flywheel ring gear of the engine. In a case of a butt engagement, the pinion gear will stop but the clutch assembly will continue to rotate. This rotation will allow the pinion gear to rotate and the pinion gear will engage onto the flywheel ring gear.
As the engine starts to run, the engine speed will eventually exceed the starting motor speed. The overrunning clutch portion of the pinion drive assembly (7) protects the starting motor from this overspeed condition. This process is done by disengaging the mechanical connection between the engine flywheel and the starting motor.
Illustration 7 g00710725
Solenoid assembly
(2) Solenoid assembly
(3) Plunger assembly
(5 ) Shift lever assembly
(16) Windings
(17) Solenoid contacts
(18) Return spring
The solenoid assembly (2) contains the following components: windings (16), plunger assembly (3) and solenoid contacts (17). When the key start switch is closed, the pull-in winding and the hold-in winding are energized. The energized windings (16) will pull the plunger assembly (3) to the left. The plunger movement pulls the shift lever assembly (5) which will allow the pinion to engage. When the solenoid contacts (17) close, full battery current is sent to the motor and the engine begins to crank. When the engine starts, the overrunning clutch protects the armature from excessive speed until the key start switch is released. After the switch is released, the return spring (18) pushes on the plunger assembly which will disengage the pinion.