Starter Motor

The starter motor is a powerful electric motor, with a small gear (pinion) attached to the end. When activated, the gear is meshed with a larger gear (ring), which is attached to the engine. The starter motor then spins the engine over so that the piston can draw in a fuel/ air mixture, which is then ignited to start the engine. When the engine starts to spin faster than the starter, a device called an overrunning clutch (bendix drive) automatically disengages the starter gear from the engine gear.

Starter Motor Planetary Type

 The starting system converts electrical energy from the batteries into mechanical energy to turn the engine over. A malfunction within the starting system will make it difficult to get the engine running.

In order to properly service the starting system, you need to understand how it operates. The starting system has five main components: the ignition switch or start button, a neutral safety switch (an option on some vehicles), the starter solenoid, the starter motor, and the batteries.

When the key is turned in the ignition switch to the start position, or the start button is pushed, electricity flows from the batteries to the starter solenoid.

Some vehicles are equipped with a neutral safety switch. If the vehicle is in gear when the key is turned, the neutral safety switch blocks the signal to the batteries, so the engine doesn't start cranking. Otherwise, the vehicle could jump forward or backward when the key is turned.

The starter solenoid is an electromagnetic switch mounted on the starter motor. When coils inside the solenoid are energized by electricity, they create a magnetic field which attracts and pulls a plunger. Attached to one end of this plunger is a shift lever. The lever is connected to the drive pinion and clutch assembly of the starter motor.

Operation of Starting System

Ignition Switch in "START" Position

Ignition Switch Start Position

When the ignition switch has been turned to the START position, Terminal 50 passes electrical current from the battery to the hold-in and pull-in coils. From the pull-in coil, the current then flows to the field coils and armature coils via Terminal C.
At this point, the voltage drop across the pull-in coil keeps the amount of electrical current flowing through the motor components (field coils and armature) small, so the motor rotates at a lower speed. At the same time, magnetic fields generated by the hold-in and pull-in coils pull the plunger toward the right against the return spring. This movement causes the pinion gear to move toward the left, via the drive lever, and mesh with the ring gear. The low starter motor speed at this stage means that the gears mesh smoothly.
The screw splines help the pinion and ring gears to mesh smoothly.

PINION AND RING GEARS ENGAGED

Pinion and Ring Gears Mesh

 When the magnetic switch and the screw splines have pushed the pinion gear to the position where it meshes completely with the ring gear, the contact plate attached to the end of the plunger turns the main switch on by short circuiting the connection between Terminals 30 and C. The resulting connection causes a heavier current to pass through the starter motor, which causes the motor to rotate with a greater torque. The screw splines help the pinion gear mesh more securely with the ring gear. At the same time, the voltage levels at both ends of the pull-in coil. The plunger is therefore held in position only by the magnetic force exerted by the hold-in coil.

IGNITION SWITCH "ON" POSITION

Ignition Switch On Position

Turning the ignition switch back to ON position from START cuts off the voltage being applied to Terminal 50. The main switch remains closed, however, so some current flows from Terminal C to the hold-in coil in the same direction as when the ignition switch is in the START position, it generates a magnetic force which pulls the plunger. In the pull-in coil, on the other hand, current flows in the opposites direction, generating a magnetic force which tries to return the plunger to its original position.
The magnetic fields set up by these two coils cancel each other out, so the plunger is pulled backward by the return spring. Therefore, the heavy current which has been supplied to the motor is cut off and the plunger disengages the pinion gear from the ring gear at about the same time.