Every time you turn the key or press the start button, your starter motor helps bring the engine to life. Although it operates for only a few seconds, it’s one of the most important components in your vehicle’s starting system.
But how does a starter motor actually work?
In this guide, we’ll explain how a starter motor starts your engine, break down its key components, explore the different starter motor types, and answer common questions about starter operation and failure.
This Article Contains
- How Does a Starter Work?
- What Happens When You Start the Engine?
- What Are the Components of a Starter Motor?
- Types of Starter Motors
- 8 FAQs on Starter Motor
Let’s dive in.
How Does a Starter Work?
The starter motor uses a small pinion gear to rotate the engine’s flywheel, allowing the engine to begin the combustion process.
When you turn the ignition key or press the start button, the battery sends power to the starter solenoid. The solenoid engages the starter gear with the flywheel and supplies power to the starter motor, which cranks the engine.
Once the engine starts, the starter gear automatically disengages to prevent damage.
Let’s take a closer look at what happens during the starting sequence.
What Happens When You Start the Engine?
Starting your vehicle takes just a few seconds, but several components work together behind the scenes to crank the engine. Here’s what happens:
- The ignition switch or start button activates the starter solenoid: When you turn the key or press the start button, the battery sends a small electrical current through the starter control circuit, energizing the starter solenoid.
- The starter pinion gear engages the flywheel: The energized solenoid pulls a plunger that moves a lever fork, pushing the starter pinion gear outward until it meshes with the flywheel ring gear.
- The starter motor receives battery power: At the same time, the solenoid closes the starter circuit, allowing high current from the battery to flow to the starter motor.
- The starter motor cranks the engine:The starter motor spins the pinion gear, which rotates the flywheel. This cranks the engine, allowing the pistons to move and the air-fuel mixture to ignite, beginning the combustion process.
- The starter disengages once the engine starts: After the engine starts, releasing the key or start button deactivates the solenoid. Return springs retract the pinion gear from the flywheel, while an overrunning clutch prevents the spinning flywheel from driving the starter motor backward, protecting it from damage.
Next, let’s break down the starter motor into pieces.
What Are the Components of a Starter Motor?
Here’s a look at the basic components of a starter motor.
1. Field Coils
The starter motor housing holds 2-4 field coils, which surround the armature. The field coil array produces a strong, stationary electromagnetic field as current from the battery passes through.
2. Armature
The armature is an electromagnet fixed onto the starter drive shaft (also called the armature shaft). It’s made of a laminated soft iron core wrapped with numerous conductor windings.
The armature shares an axle with the commutator, which provides the current to generate an electromagnetic field. The reaction between the armature and the field coil magnetic fields is what rotates the armature.
3. Commutator And Brushes
The commutator is located at the rear of the starter motor housing. It’s made of two plates attached to the axle of the armature shaft. Carbon brushes connect to each plate, providing an electrical connection for the armature windings.
4. Solenoid
The starter solenoid functions as a powerful electric relay.
A typical starter solenoid has a small connector for the starter control circuit wire (connected to the ignition key) and two larger terminals: an input terminal for the positive battery cable and an output for the cable that powers the starter motor itself.
The solenoid usually has two coils of wire wrapped around a movable plunger.
The coils do this:
- A strong closing coil draws in the plunger
- A weaker coil holds the plunger in position — when this happens, current is removed from the strong coil, saving some power
When activated through the control circuit, the solenoid also extends the pinion gear to mesh with the flywheel ring gear, closing the starter circuit to send battery voltage to the starting motor.
6. Plunger
The plunger works with the solenoid to connect battery power to the starting motor and pull in the lever fork.
7. Lever Fork
The lever fork is attached to one end of the plunger. When the plunger moves into the solenoid core, the lever fork pushes out the pinion gear to mesh with the flywheel ring gear.
8. Pinion Gear (Drive Gear, Starter Gear)
The pinion gear turns the engine flywheel ring gear. It’s also called a drive gear or starter gear and is part of what’s sometimes known as a starter Bendix drive.
It’s attached to the armature drive shaft, often through an overrunning sprag clutch. The sprag clutch allows the pinion gear to transmit drive in only one direction.
So, if the pinion stays engaged with the flywheel (which can happen if the ignition key isn’t released when the engine starts), the pinion will spin independently of the drive shaft. This prevents backdrive and damage to the starter motor.
It’s important to note that the starter motor has evolved over time, and we now have various types of starters.
Let’s take a look.
Types Of Starter Motors
Here’s an overview of some common types of electric starter motors:
1. DD – Direct Drive
The DD is the most common type of starter motor and is usually solenoid-operated. The drive gear (pinion gear) on the DD is attached directly to the armature, thus “direct drive.”
2. PLGR — Planetary Gear
The PLGR starter motor uses a planetary gear assembly located between the armature and the pinion gear. The planetary gear assembly allows a gear reduction which increases torque at a significantly reduced starter motor speed, and in this way, cutting current demands.
3. PMGR — Permanent Magnet Gear Reduction
The PMGR starter motor was designed to lessen the weight, ease construction and reduce heat generation. Instead of using the heavier field coil assembly, the PMGR employs permanent magnets.
4. PMDD — Permanent Magnet Direct Drive
As its name suggests, the PMDD is a direct drive starter motor that uses permanent magnets in place of field coils.
5. OSGR — Off-Set Gear Reduction
The OSGR starter motor was designed to work with high speed and low current. Its internal gear sets are offset, meaning the drive gear and starter motor rotate on different axes.
Now that we’re familiar with how a starter motor works, let’s go through some FAQs.
8 Starter Motor FAQs
Here are answers to some starter motor questions you may have in mind:
The starter motor is a device used to turn over or “crank” an internal-combustion engine. It typically consists of a starter solenoid and a powerful motor starter.
The electric starter motor is commonly found in petrol or small diesel engines, but it isn’t the only kind.
Other types include the:
– Inertia starter: This is a variant of the electric motor starter used on aircraft with large radial piston engines
– Hydraulic starter: This offers a sparkless, reliable method of engine starting for applications like remote generators or lifeboat propulsion engines
– Manual starter: This consists of an on/off switch and an overload relay, and is typically used for smaller motors like small pumps and power saws
The internal combustion engine runs on a feedback loop, relying on inertia from its cycles to run on its own. An engine needs air, fuel and a spark to run unassisted, but something has to start the cycles — which is where the starter motor comes in.
Once the starter motor has initiated engine function, rotational energy from the engine feeds off a drive belt that powers different components like the alternator or power steering pump.
In most vehicles, the starter motor is bolted to the engine or transmission. An easy way to find it is to follow the thick cable from the positive battery terminal.
The starter motor’s electrical components are typically designed to operate for 30 seconds at the most, before overheating. Most manuals instruct for a pause of at least 10s after each 10-15s of engine cranking if an engine doesn’t immediately turn over.
And if it still won’t crank, it might be time to call in your mechanic.
A faulty starter can stem from several issues. Here are some causes that can manifest as a starter problem:
– Burned, worn-out, or dirty solenoid contacts stop the starter circuit from closing
– Worn-out carbon brushes fail to deliver current to the starter motor
– The pinion gear doesn’t mesh correctly with the engine flywheel
– Insulation on the armature winding starts to break down, reducing the starter’s ability to generate torque
– The starter neutral safety switch fails or is out of adjustment
– The ignition switch fails, so the solenoid isn’t activated
Here are the typical symptoms you’ll encounter if you have a bad starter motor:
– Clicking noise: Your car battery is fully charged, but there’s only a clicking noise when the ignition key is turned. This is the sound of the starter solenoid engaging, but the starter motor doesn’t power up.
– Grinding noise: The starter motor runs but fails to turn over the engine, and there’s a painful grinding noise. This could be the sound of the starter pinion gear failing to mesh correctly with the engine flywheel ring gear.
The starter motor uses power from the battery to crank the engine when you turn the key or press the start button. Once the engine starts, the starter motor switches off.
The alternator takes over after the engine is running. It generates electricity to recharge the battery and power electrical systems such as the headlights, radio, and climate control.
In short, the starter motor starts the engine, while the alternator keeps the battery charged and supplies power while you drive.
The starter system plays a vital role in your vehicle’s engine function. If your car won’t start, you do have the option of troubleshooting it yourself.
However, a starter problem can often mimic that of a bad battery or bad alternator — and are sometimes interconnected. To ensure all your starting issues are resolved, it’s best to let a professional see to it.
And you’re in luck, as AutoNation Mobile Service is readily available to help you out. We are a convenient mobile auto maintenance and repair solution.
Here are some benefits:
– Vehicle maintenance and repairs can be made right in your driveway
– Expert technicians perform auto inspection and servicing
– Competitive and upfront pricing
– Online booking is convenient and easy
– All vehicle repairs and maintenance are completed with high-quality tools and replacement components
– A 12-month | 12,000-mile warranty for all repairs
For an accurate cost estimate for a starter motor replacement, just fill this online form.
Keep Your Vehicle Starting Reliably
The starter motor is a neat little device that forever eliminated the need to hand crank a car engine. It’s also a component that rarely fails, despite the amount of power it harnesses each time it starts your car.
However, if you do run into a starter problem, don’t worry.
Just contact AutoNation Mobile Service.
Our expert mechanics will be in your driveway in no time to help you get that starter issue fixed up!