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The cranking motor is bolted to the flywheel housing. See Figure 20536 . ‪

Cranking Motor Mounting


To prevent excessive overrun and damage to the drive and armature windings, the switch should be opened immediately when the engine starts. A cranking period should not exceed 15 seconds without stopping to allow the motor to cool for at least 15 seconds. ‪

When the cranking circuit is closed, a drive pinion on the armature shaft engages with the teeth on the engine flywheel ring gear to crank the engine. When the engine starts, it is necessary to disengage the drive pinion to prevent the armature from overspeeding and damaging the cranking motor. To accomplish this, the cranking motor is equipped with an over-running clutch within the drive pinion. The cranking motor drive pinion and the engine flywheel ring gear must be matched to provide positive engagement and to avoid clashing of the gear teeth. ‪

Note: Some engines may be equipped with air starters. Contact starter manufacturer for operating characteristics and rebuilding procedures.

The 42 MT cranking motor typically used on the engine has a nose housing that can be rotated to obtain a number of different solenoid positions with respect to the mounting flange. The commutator end cap can be removed to inspect the brushes, in most cases, without removing the cranking motor from the vehicle. ‪

Note: The 50 MT cranking motor is used on heat exchanger-cooled pleasure craft marine engines.

The cranking motor armature is supported by three sintered bronze bearings located, one each, in the nose and intermediate housings, with one in the commutator end cap. See Figure 20537 . ‪

1. O-ring ‪

10. Shift Mechanism (Totally Enclosed) ‪

2. End Cap (Removal for Inspection) ‪

11. Two-piece Housing ‪

3. Bronze Bearing ‪

12. O-ring ‪

4. Connector Strap ‪

13. Shaft ‪

5. Gasket ‪

14. Heavy-duty Drive Overrunning Clutch ‪

6. Low Friction Bushing ‪

15. Shaft ‪

7. Seamless, One-piece Solenoid Case ‪

16. O-ring ‪

8. O-ring ‪

17. Shaft Seal ‪

9. Sealing Boot ‪

18. One-piece Brush ‪

Typical Cranking Motor Cross-section

Sintered bronze bearings used in the current cranking motors have a dull finish, compared to the former machined, cast bronze bearings, which had a shiny finish. ‪

The cranking circuit may contain a key start switch or push switch (or both), a relay, magnetic switches, solenoids, oil pressure switch, fuel pressure switch, and other protective devices. For the complete cranking circuit, refer to the vehicle manufacturer's wiring diagram. ‪

For basic cranking circuit, see Figure 20538 . ‪

Basic Cranking Circuit

A solenoid, mounted on the cranking motor housing, operates the over-running clutch drive by linkage and a shift lever. When the start switch is closed, the magnetic switch contacts close, and the solenoid windings are connected to the battery. 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 the cranking takes place. ‪

Repair of Cranking Motor

Refer to the OEM guidelines for cranking motor repair procedures. ‪

Removal of Cranking Motor

Precleaning is not necessary. ‪

Remove the cranking motor as follows: ‪


To avoid injury from electrical shock, follow OEM furnished operating instructions prior to usage.

  1. Remove the ground strap or negative cable(s) from the battery(s).
  2. Tag each lead to ensure correct connections when the cranking motor is reinstalled.
  3. Disconnect the cranking motor cables and solenoid wiring.
  4. Support the motor, and remove the three bolts which secure it to the flywheel housing.
  5. Pull the motor out to remove it from the flywheel housing.

If the nose housing requires relocation, perform the following steps: ‪


The solenoid should not be located below the centerline of the cranking motor. Dust, oil, moisture and foreign material can collect and cause solenoid failure. ‪

  1. Remove the six socket-head screws (one short and five long) and six neoprene plugs from the unused holes if a twelve-hole mounting flange is used.
  2. Turn the nose housing to the required position.
  3. Install the six socket-head screws, with the short screw in the shallow hole nearest the solenoid and six neoprene plugs, if a twelve hole mounting flange is used.
  4. Torque the screws to 18-23 Nm (13-17 lbft).

Installation of Cranking Motor

Install the cranking motor as follows: ‪


To avoid injury from electrical shock, follow OEM furnished operating instructions prior to usage.

  1. Support the cranking motor, and install the three bolts that secure it to the flywheel housing.
  2. Connect the cranking motor cables and the solenoid wiring.
  3. Install the ground strap or negative cable(s) to the battery(s).
  4. If an aluminum flywheel housing is used, torque the cranking motor attaching bolts to 187-209 Nm (138-154 lbft). If a cast iron flywheel housing is used, torque the cranking motor attaching bolts to 245-306 Nm (181-226 lbft).
  5. If equipped with a 42 MT or 50 MT starting motor, install wiring terminal leads to the cranking motor and the solenoid switch.
  6. Torque the smaller connections to 1.8-3.4 Nm (16-30 lb in.). Torque the larger connections to 27-34 Nm (20-25 lbft).

    Note: Keep all of the electrical connections clean and tight.

  7. Refer to section for verification of proper cranking motor installation.