Starter Motor: What is it & How does it Work?

The starter motor is one of the most important parts of the internal combustion engine. It helps to start the engine. This part of your car initially turns the crankshaft and starts the engine. This article mainly explains the starter motor working, types, and replacement cost.

What is Starter Motor?

A starter motor is a mechanical device used to turn the crankshaft of the IC engine so as to start the initial operation of the engine under its power. The starter is also known as a starter motor, cracking motor, or self-starter. These are electrically, pneumatically, or hydraulically operated motors.

Starter Motor Diagram

The main function of the starter motor is to initially turn the engine crankshaft and start the engine. When the engine starts to run, the starter disconnects from the engine; after that engine depends on the power produced by the air-fuel mixture combustion process.  

The electric starter contains a powerful solenoid and a Direct Current (DC) motor. The solenoid is directly connected to the battery of the car. It gets heart current power from the engine body while the positive current comes directly from the battery.

The vehicle must have a 12-volt battery to start the motor. In simple words, your vehicle battery must have adequate power to run the motor. In some cases, the starter clicks, but it doesn’t start; the problem is with the battery or the starter motor itself.

The main function of the starters is to initially turn the engine crankshaft one or two times required to start the engine.

Working of Starter

The working of the starter is very simple and easy to understand. It contains four field windings installed inside the housing. The armature is linked to the field coils via carbon. The starter motor gets power from the vehicle battery.

Working of starter

As you press the ignition key, the battery activates and transfers power to the solenoid.

The solenoid further transfers power to the starter motor. When the starter motor gets power, it pushes the pinion gears forward to mesh with the engine flywheel. The flywheel is connected to the crankshaft of the engine.

As the motor turns, the flywheel also turns, which further turns the crankshaft of the engine. When the crankshaft turns, the engine starts, and the combustion process of the air-fuel mixture starts. As the combustion process starts, the motor stops, and the engine further gets power through the combustion of the air-fuel mixture.

Parts of Starter

The starter motor has the following parts:

  • Commutator
  • Armature
  • Brushes
  • Lever Fork
  • Piston or Plunger
  • Solenoid
  • Field Coils
  • Pinion

1) Commutator

It is an electrical switch that periodically reverses the current between the external circuit and the motor. The commutator consists of two plates attached to an armature shaft. These plates ensure proper connection for the coils of the electromagnet.

2) Armature

The armature is one of the parts of the starter. It is installed on the bearing or driveshaft for a guide. The armature consists of a laminated soft iron core. Multiple conductor windings or loops use to cover this core.

3) Brushes

The brush is the part that runs in the commutator section on the back of the case. It shines the commutator to conduct electricity.

4) Lever Fork

It connects to the plunger. It moves forward along with the plunger to engage the pinion.

5) Piston or Plunger

It is installed at the end of the pinion. As it moves forward, it engages the pinion.

Read More: Piston Working and Types

6) Solenoid

The solenoid or electromagnet has two coils wound around an iron core. It acts as a switch to start and stop the electricity flow between the car battery and the starter motor.

7) Field Coils

The field coils are installed inside the casing of the starter motor. The motor has two or more coils connected in series.

As the coils get electricity from the battery, they convert it into an electromagnet and rotate the armature. When the armature rotates, the magnetic field is produced around the armature.

8) Pinion

It contains springs and gears. As the motor starts, the pinion immediately engages and starts the engine.

Types of Starter Motor

The starter motors have the following types:

  • Planetary Gear Reduction (PLGR)
  • Direct Drive (DD) Starter Motor 
  • Permanent Magnet Gear Reduction (PMGR)
  • Inertial Starter
  • Off-Set Gear Reduction (OSGR)
  • Permanent Magnet Direct Drive (PMDD)

1) Planetary Gear Reduction (PLGR) Starter

The existence of this type of starter has largely replaced direct-drive starters. It contains a permanent magnet that transfers power between the armature and the pinion shaft. The armature of this gear rotates faster.

Planetary Gear Reduction

The planetary gear starter motor contains three plenary carrier gears and one sun gear. The sun gear installs at the armature end while the plenary gears install within the ring gear and held stationary.

2) Direct Drive (DD) Starter Motor

It is one of the most famous and oldest types of starters in the market. The working of the direct drive is simple as other types. It is a solenoid-operated device. There are multiple designs of direct drive starters available in the market.  

Direct Drive Starter Motor

The solenoid is directly connected to the vehicle battery. As you press the ignition switch, the solenoid receives power from the vehicle battery.

As the solenoid gets power, it pushes the plunger and moves the lever that guides the pinion. This pinion then engages with the flywheel of the engine. So, when the starter turns, the flywheel also spins, which starts the combustion process in the engine combustion chamber.  

3) Permanent Magnet Gear Reduction (PMGR)

These types of starters have low heat build-up, are lightweight, easy to install and construct. The permanent magnet gear reduction PMGR has 4 to 6 magnet field packs.

Permanent Magnet Gear Reduction

The 12V solenoid of the starter has three terminals and heavy-duty construction to reduce the current requirement. This type doesn’t contain a field coil. Therefore, the brush and commutator transmit power directly to the armature.

4) Inertial Starter

They are electric types that have the ability to gain the characteristics of all other starter motors. They work efficiently on startup and also protect the motor parts.

Inertial Starter

They start the engine powerfully and very quickly. They are best suitable for high speeds. The weight linked to the torque capacity of the starter motor is very low.

5) Off-Set Gear Reduction (OSGR)

These types of starter motors operate at low currents and high speeds. Off-set gear reduction starters have a lightweight, easy assembly, and compact design. They are most commonly used on 4WD vehicles because they increase starting torque.

Off-Set Gear Reduction

6) Permanent Magnet Direct Drive (PMDD)

It is similar in some respects to direct drive. The difference between the PMDD and the direct drive is that the PMDD uses a permanent magnet instead of the field coils.

Permanent Magnet Direct Drive starter

Sings of Bad Starter Motor

When your starter motor goes bad, it produces one or more of the below-given signs:

  • Engine Won’t Start
  • Whirring or Clicking Noise
  • Overheating and Smoking 
  • Dashboard lights up, but the engine won’t start
  • Hard to Start the Engine

1) Engine Won’t Start

As the starter motor goes bad, your vehicle engine won’t start. The engine won’t start due to many other reasons such as a bad ignition key, damaged solenoid, engine’s internal problems, or failed battery.

2) Whirring or Clicking Noise

The clicking or whirring noise is one of the major symptoms of a bad starter motor. When the starter goes bad, you may hear a clicking noise as you turn the ignition key.

As the parts of the starter are worn or don’t work efficiently, you may hear a clicking or whirring similar noise one you notice when the driver accidentally presses the ignition key after starting the engine.

When you hear the whirring, grinding, or clicking noise, you must stop the vehicle and inspect the problem. If your starter has been damaged, you should replace it as soon as possible.

3) Overheating and Smoking 

Engine overheating is one of the common signs of a damaged or faulty starter motor.

The engine overheating leads to an unpleasant smell of smoke inside and around the car. Such a situation indicates that too much current is flowing through the motor. This overheating issue occurs due to short circuits, ignition switch problems, or other mechanical issues if the starter runs for a long time and the car won’t start.

4) Dashboard lights up, but the engine won’t start

If your vehicle battery is supplying power properly, but the engine is not starting, it means that your vehicle has a bad or damaged starter. Especially if you recently charged your battery.

5) Hard to Start the Engine

If you try to start the vehicle engine and it doesn’t start right away, and then you try again, and it starts, there are high chances that your vehicle starter is faulty. There may be a problem with the starter relay.

If your vehicle starter relay is bad, it will not properly send power to the starter motor. If the relay is faulty, the motor may produce a clicking noise when turning the ignition key.

Starter Motor Replacement Cost

The replacement cost of a starter motor varies according to your vehicle model, labor cost, and type of brand. The average replacement cost of the starter motor is from $200 to $1200. In this cost, the labor cost is anywhere between $140 and $1,000.

FAQ Section

What are the causes of a bad starter?

The starter motor goes bad due to multiple reasons. The following are the most common causes of a bad starter.

  • Battery corrosion
  • Oil leakage
  • Engine overheating
  • Damaged or faulty parts of the starter motor
  • Insufficient power supply by the battery
  • Loose wiring to and from the starter
  • Damaged solenoid
  • Bad fuse or relay
  • Corroded connections at the starter end

How do troubleshoot starter problems?

  1. First of all, look under the hood.
  2. Use a hard object and lightly tap the starter for just a few minutes
  3. Now adjust the transmission
  4. Check the fuel gauge

What is the lifespan of a starter motor?

The lifespan of a starter motor depends on the vehicle model and how you maintain it. However, you can expect to get about 100,000 miles out of the factory starter.

What are the types of the starter motors?

  • Planetary Gear Reduction (PLGR)
  • Direct Drive Starter Motor
  • Permanent Magnet Gear Reduction (PMGR)
  • Inertial Starter
  • Off-Set Gear Reduction (OSGR)
  • Permanent Magnet Direct Drive (PMDD)
Read More

Leave a Comment