37-MT, 41-MT, and 42-MT Series Starting Motors Component Description

Illustration 1 g00718697

(1) Rear Housing

(2) Solenoid

(3) Plunger

(4) Shift Lever Housing

(5) Shift Lever

(6) Drive Housing

(7) Pinion Drive

(8) Brushes

(9) Brush Holder

(10) Pole shoes

(11) Field Winding (Coil)

(12) Armature

(13) Starting Motor Housing

The major components of the starting motor are the following items:

•Starting motor housing (13)

•Field winding (coil) (11)

•Pole shoes (10)

•Armature (12)

•Brushes (8)

•Brush holder (9)

•Pinion drive (7)

•Shift lever (5)

•Plunger (3)

•Solenoid (2)

•Housings (1), (4), and (6)

Illustration 2 g00718701

Field Winding and Starting Motor Housing

(10) Pole Shoes

(11) Field Winding (Coil)

(13) Starting Motor Housing

The starting motor housing (13) supports the field winding (coil) (11), the pole shoes (10), the brush holder (9), and the brushes (8). These parts are removable. The field winding (11) and the pole shoes (10) provide the magnetic field for the armature. The field winding also contains a shunt coil on 37-MT starting motors. The armature rotational speed is limited by the shunt coil during engagement. This prevents damage to the pinion drive.

Illustration 3 g00718702


(12) Armature

Armature (12) consists of a laminated iron core which is assembled on the armature shaft. The armature also has a commutator on one end. The commutator is made of copper segments (bars) insulated from each other and insulated from the armature shaft. The armature windings are wound in the slots of the core. The armature windings are also connected to the commutator segments.

The armature is positioned in the field winding and the pole shoes. The armature is supported by the brushings in the drive housing (6), the shift lever housing (4), and the rear housing (1) .

The armature and the field winding are connected in series. The same current flows through each component. This generates high torque primarily when the motor is first started.

Illustration 4 g00718703

Brush Holder

(9) Brush Holder

(14) Brush Springs

The brush holder (9) is mounted over the commutator to the starting motor housing. Four brushes are held against the commutator. Brush springs (14) keep pressure on the brushes so the brushes stay in contact with the commutator. Two brush holders are connected to the field winding positive (+) leads. The two negative brush holders are not insulated from the brush holder assembly onthe 37-MT and 41-MT starting motors. The two negative brush holders are connected to the negative terminal on the 42-MT starting motors.

Illustration 5 g00718704


(8) Brush

The brushes (8) are made of carbon. The brushes (8) conduct electricity. The brushes transmit current from the field winding to the commutator. There are four brushes. Two brushes are positive and two brushes are negative.

Illustration 6 g00718705

37-MT Pinion Drive

(7) Pinion Drive

(15) Pinion Gear

Illustration 7 g00718708

41-MT and 42-MT Pinion Drive

(7) Pinion Drive

(15) Pinion Gear

As the engine starts to run, the speed eventually exceeds the starting motor speed. The overrunning clutch portion of the pinion drive (7) protects the starting motor from this overspeed condition. The mechanical connection between the engine flywheel and the starting motor is disengaged.

The pinion drive (7) has a pinion gear (15) that engages the flywheel ring gear. The pinion gear will stop in case of butt engagement on the 37-MT starting motors. The pinion drive spring is compressed by the shift lever until the solenoid contacts meet the solenoid terminals as a result. The starting motor is now turned on. The starting motor turns the pinion until the pinion meshes with the ring gear. The pinion gear will stop in case of butt engagement on the 41-MT and 42-MT starting motors. The clutch assembly continues to rotate. This rotation will allow the pinion gear to rotate and the pinion gear will engage onto the flywheel ring gear.

Illustration 8 g00718709


(2) Solenoid

(3) Plunger

(5) Shift Lever

(16) Windings

(17) Solenoid Contacts

(18) Return Spring

Solenoid assembly (2) contains the following components: windings (16), plunger (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 (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 pinion drive protects the armature from excessive speed until the key start switch is released. After the switch is released, the return spring (18) moves shift lever (5) to the right which will disengage the pinion.

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