How To Understand the Main Parts of a Starter Motor ??

By Magari Poa on 25/09/2025

Ever wondered what really happens when you turn the key or push the start button in your car? Behind that simple action lies a crucial component — the starter motor. Without it, your engine wouldn't fire up.

In this guide, we'll break down the main parts of a starter motor and explain what each one does in simple terms.

1. Starter Motor

This is the heart of the system. It's an electric motor designed to turn your engine's crankshaft just enough to get it running. Once the engine catches, the starter disengages.

2. Bendix Gear (Starter Pinion)

The Bendix gear is a small but mighty part. It temporarily connects with the engine's flywheel when starting. Think of it as the handshake between your starter motor and the engine.

3. Solenoid

The solenoid is both a switch and a pusher.

It pushes the Bendix gear forward to engage with the flywheel.
It also sends electrical current to the starter motor to begin cranking.

If you ever hear a "click" but no start, the solenoid could be the culprit.

4. Terminals

The starter motor has two important terminals:

Battery Terminal (+): Direct connection from the battery for power.
Control Terminal (S): Activated when you turn the ignition key or push the start button.

5. Fork (Shift Lever)

The shift lever (or fork) is what physically moves the Bendix gear into position to mesh with the flywheel when you start the car.

6. Field Coils (Stator)

Field coils generate the magnetic field inside the motor, which allows the armature (rotor) to spin.

7. Armature (Rotor)

The armature is the rotating part. Once energized, it spins rapidly, cranking the engine until it fires.

8. Brushes (Carbons)

Brushes act as the conduits of electricity. They transfer electrical current to the spinning armature, ensuring smooth operation.

9. Commutator

The commutator works with the brushes to control the direction of current flow, keeping the motor spinning efficiently.

10. Front & Rear Housing

These are the outer casings that hold everything together, protect the internal components, and support the rotating shaft.

11. Overrunning Clutch (Bendix Clutch)

This clutch prevents the starter from being damaged. Once the engine starts running on its own, the clutch disengages the starter motor.

Pro Tip: Spotting Starter Motor Trouble

A failing starter can cause:

Slow cranking
Clicking sounds without engine turning
Grinding noises (if the Bendix gear misaligns)

If you experience these, check the solenoid, brushes, or Bendix gear first.

Now you know what's happening under the hood every time you start your car! Understanding your starter motor helps you diagnose issues early and avoid costly breakdowns.