Starter Motor: Parts, Working, Types & Symptoms & Solution [PDF]

In this article, we shall be covering the Starter Motor. It’s working along with a diagram. Discuss its Parts, Types, and Uses. We have also Shared a PDF at the end.

What is Starter Motor

The starter motor, a high-torque device essential for initiating combustion cycles in internal combustion engine vehicles, is a core component of the starting system. Alongside the ignition switch, starter relay, safety switches, flywheel ring gear, and battery, it forms interconnected circuits for engine activation.

Composed mostly of metal parts, the starter motor assembly includes an electric motor, a drive mechanism, and a solenoid serving as a switch and actuator. Often mounted to the engine or transmission, its strategic positioning ensures seamless engagement with the flywheel’s ring gear.

Various engagement methods are employed for this purpose. The necessity of a starter in vehicles lies in its capability to provide the external force required to turn over and start the engine, facilitating the combustion process.

Functions of Starter Motor

Initiating your car engine relies on a crucial component—the starter motor—for two primary reasons. Firstly, the engine cannot independently initiate combustion at zero rpm, necessitating an external force. The starter motor provides this external force factor. It is commonly found in vehicle starter systems.

The starter motor serves a dual purpose. Its initial role involves converting electric energy from the battery into mechanical energy. Simultaneously, it engages with the flywheel, facilitating the necessary cranking motion to set the engine in motion. Without the starter motor’s intervention, commencing the engine becomes a difficult task.

Despite its size, the starter motor operates efficiently, utilizing a small gear featuring a significant gear reduction ratio. This ratio typically falls within the range of 15:1 to 20:1 in various automotive applications. This mechanical precision ensures a smooth and controlled initiation of the engine.

What is Starter Motor
Starter Motor Functions

Parts of Starter Motor

The Parts of the Starter Motor are as follows


  • Electromagnetic guide on driveshaft.
  • Contains a laminated soft iron core with wound conductors.


  • Located at the shaft’s back for brush-conducted electricity.
  • Comprises two plates connecting the electromagnet’s coil.


  • Two wire coils around a core.
  • Functions as a switch for electrical connection.


  • Transfer current from static to dynamic conductor.
  • Conduct electricity by rubbing against the commutator.


  • Initiates pinion engagement for the motor start.

Lever Fork

  • Linked to the plunger, engages pinion when pushed forward.


  • The device with gears and springs.
  • Extends to flywheel teeth post-engine start.

Field Coils

  • Two or more coils in series.
  • Secured by screws, powered by battery to create electromagnet for armature rotation.

Working of Starter Motor

The starter motor consists of essential components: the motor, a solenoid, and a pinion, often with a gear reduction mechanism. Its operation involves an armature within a magnetic field, initiated by current flow through the ignition circuit.

Upon activating the ignition, the starter relay powers the solenoid, directing current to the motor. The solenoid engages a lever, meshing the pinion gear with the flywheel or flexplate, initiating engine turnover.

Starter Motor Working
Starter Motor Parts

After releasing the ignition, the relay cuts power, and the solenoid disengages, retracting the pinion. Manufacturers employ methods like inertia or solenoids with one-way clutches for smooth engagement.

In certain motors, inertia guides the pinion along a splined shaft, using the flywheel’s speed for disengagement. Modern starters use gradual speed increases and one-way clutches to prevent damage during engagement.

Types of Starter Motor

Starter motors vary in design, each tailored to specific needs. The classification revolves around the type of magnet, engagement method, and torque multiplication. Here’s a brief overview:

Types of Starter Motors

Direct Drive Starter Motor (DD)

  • Traditional and widespread, operated by a solenoid.
  • Upon ignition activation, the solenoid engages the pinion gear, meshing with the engine flywheel to start combustion.

Planetary Gear (PLGR)

  • Replaces direct-drive types, utilizing a permanent magnet for power transfer.
  • Achieves significant gear reduction, reducing the demand for high current during operation.

Permanent Magnet Gear Reduction (PMGR)

  • Lighter and simpler than field coil starters, with four to six magnet field assemblies.
  • Features a 12V solenoid with three terminals, providing heavy-duty performance with lower current requirements.

Permanent Magnet Direct Drive (PMDD)

  • Resembles direct-drive starters but replaces the field coil with permanent magnets.

Off-Set Gear Reduction (OSGR)

  • Operates at high speeds with low currents, commonly used in four-wheel-drive vehicles.
  • Simple assembly, lighter, and more compact, offering enhanced cranking torque.

Inertial Starter

  • Versatile electric starter performing all starter functions.
  • Ensures quick and powerful engine starts, particularly effective for breaking speed.
  • Minimal weight-to-torque ratio, making it an optimal choice for robust performance.

Types of Starters

Permanent Magnet Starter

  • Relies on permanent magnets for armature rotation.
  • The compact design has no internal coils and often includes a gear reduction mechanism for torque.

Field Coil Starter

  • Utilizes electromagnets, resulting in a larger size.
  • Powerful but may strain and drain the battery quickly, lacking a gear reduction drive.

Inertia Starter

  • Traditional design uses the principle of inertia.
  • Simple construction with a splined shaft and pinion, but known for violent engagement and quick wear.

Pre-engaged Starter

  • Modern design with a solenoid-driven pinion.
  • Ensures smoother engagement and disengagement, with less wear on the pinion gear.

Gear Reduction Starter

  • Features a gear setup to increase torque.
  • Powerful and compact design, minimizing battery drain, suitable for demanding applications.
Types of starter
Car Starter Types

Symptoms of a Failing Starter Motor

Engine Won’t Start

  • Turning the key with no response signals potential starter motor failure.
  • Possible causes include a burned-out solenoid, a fused motor, or a dead battery.

The Starter Cranks, But the Engine is Unpowered

  • The starter turns, but the engine fails to start, indicating potential mechanical issues.
  • Possible problems with the flywheel’s gears require prompt starter replacement.

Grinding Noises

  • Defective or worn starter gears can create grinding sounds.
  • Address this promptly to prevent damage to the flywheel, leading to costly repairs.

Smell or Smoke While Starting

  • Overheating due to continuous power supply may result in a burning smell or smoke.
  • Potential causes include ignition switch issues or a blown fuse.

Lights Dim When Starting

  • Dimming interior or dashboard lights indicate starter motor failure.
  • Excessive power drawn from a short circuit in the internal wiring necessitates replacement.

Whirring Noise

  • A whirring sound during cranking suggests improper engagement of the starter pinion gear.
  • This prevents the engine from starting and requires attention.
Symptoms of Bad Starter Motor
Starter Motor Remedies

Solutions for Starter Motor Issues

Examine Battery and Cables

  • Check the battery and cables for damage or weakness.
  • Address cable issues or replace a weak or dead battery.

Tap the Starter

  • Gently tap the starter motor’s body with a light spinner.
  • Handle with care to avoid damaging the component.

Transmission Adjustment

  • In an automatic gearbox, shift from park to neutral if the starter won’t turn on.
  • If the car starts in neutral, there may be a technical issue preventing starting in the park.

Price of Starter Motor

The price of a car engine starter varies by type, application, and manufacturer. Choosing between OEM and aftermarket components is crucial, with aftermarket starters generally more budget-friendly.

Starter Motor price
Price of Starter Motor

Aftermarket starter prices range from $100 to $200, while OEM models can reach up to $500. Larger engines or luxury vehicles may incur higher costs due to the need for a heavy-duty starter.

When purchasing, ensure the starter aligns with your car’s specifications. Online shopping is simplified by providing details like make, model, and manufacturing year. Consider brand reputation for an informed decision.


In conclusion, the starter motor is a critical element in a vehicle’s starting system, initiating combustion cycles and converting electric energy for engine activation. Understanding its types, functions, and troubleshooting methods is essential. Whether opting for aftermarket or OEM replacements, aligning with the vehicle’s specifications ensures optimal performance and reliable starts.

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