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Most of us have had that nightmare situation — you’re running late for work, you get in the car and turn the key. Nothing. Maybe a slight clicking or chugging noise. Unless you’re a qualified mechanic, you probably won’t be able to tell what’s causing the problem. 


There are a few main reasons your car won’t start: the battery, the ignition switch and the starter motor. A faulty starter motor is one of the most common breakdown causes in the UK, so it’s good to learn how a starter motor works. That way, when something goes wrong, you’ll know what it is and have a good excuse for being late to the office.

That’s why we’ve put this guide together, to help you understand precisely how a starter motor works. It explains all you need to know about starter motor parts and stopping them from breaking, and, importantly, what to do if your car won’t start. 

How a Starter Motor Works 

If you’ve never had an issue with your starter motor, you might not know just how important it is to get your car going. Ordinarily, when you turn the ignition key, the engine will turn over, crank and start. 

The starter motor is vital in this process. When you turn the key or press the start button in your car, it engages a solenoid switch on the starter motor. The starter motor will then mesh with a gear to rotate the engine crankshaft and get the car started. Without the starter motor, the engine doesn’t have enough energy to start. 

Most starter motors contain about eight parts. So there’s a lot of potential for any one of them to stop working and leave you banging your head on the steering wheel. Usually, a starter motor contains: 

  • Armature — This is a soft iron core wrapped in several conductor windings that create an electromagnet. It’s attached to the driveshaft for support.

  • Commutator — Made up of two plates, an axle and conductor brushes, this provides electricity to the armature. It’s found at the rear of the starter motor housing.

  • Brushes — Part of the commutator, the brushes conduct electricity at the back of the starter motor housing for the electromagnet.

  • Plunger — Connected to the vehicle battery and solenoid, the plunger moves forward to engage the pinion.

  • Pinion — Made up of a combination of gears and springs, the pinion engages the flywheel, spins the engine and starts the internal combustion.

  • Level Fork — Connected to the plunger, it helps to engage the pinion.

  • Armature Coils — Part of the armature, these are usually two or four field coils connected in a series to create a magnetic field.

  • Solenoid — This contains two coils of wire around a moveable core and works as a switch for the starter motor. The starter solenoid connects the starter motor to the car’s battery. 

How Does the Starter Solenoid Work?

The solenoid switch is a relatively simple part of the starter motor. It consists of a battery, a pull-in and hold-in coil and an iron plunger. When you start your car, the car’s battery sends voltage to the solenoid, which allows the pull-in coil to create a magnetic field.

This magnetic field draws the plunger into the core and completes the electric circuit. This causes the pinion to mesh with the engine flywheel and starts the engine. The hold-in coil uses a weaker magnetic field to keep the plunger in place. 

What Kills a Starter Motor? 

Starter motors, unfortunately, don’t last forever. As the starter motor gives the kick of kinetic energy to get your car revving, it goes through a lot of stress and deteriorates over time. The pressure varies depending on your car’s size and age, but it will eventually stop working. 

But there are some things that you can do to make sure that yours lasts as long as possible. These simple checks and general maintenance could get you hundreds, if not thousands, more miles out of your car. 

  • Make sure that all terminals, connectors and the solenoid are clean. If any of these are dirty, they can quickly corrode and wear away, which reduces the current available. This means that your starter motor will have to work harder and will wear out faster.

  • Check your flywheel thoroughly. As the flywheel is so integral to your car starting, it goes through a lot of stress. Over time, it can crack, wear away and lose its teeth, making the pinion gear less effective and wearing out your starter motor. 
  • Keep everything tight. Every part of your starter motor goes through a lot of pressure daily, so it’s a good idea to make sure the bolts and mounts are tight. If any of them are loose, they can cause a bad connection and wear out the starter motor. 

How Do You Diagnose a Starter Problem? 

The first thing you should do to diagnose if you have a problem with your starter motor is to check that something else isn’t causing the issue. There are more common causes of breakdowns, so checking these first will save you a lot of time and make you reasonably sure of the problem when you speak to a mechanic. You’ll need to check:

  • How much fuel you have in the tank
  • Whether you have any security lights on
  • If your battery has enough charge
  • If your battery cables are all attached correctly
  • Whether your anti-theft system hasn’t immobilised the starter motor.

If you check these issues and cannot determine the cause, your starter motor is likely the culprit. There are some warning signs to look out for before the starter motor will stop working, such as: 

  • Metal grinding noises — If the starter motor can’t engage the flywheel, it causes metal grinding. This can damage both the starter motor and the flywheel. 
  • Whining noise — This occurs when there isn’t enough engagement between the starter motor and the flywheel, known as freewheeling. Listen out for a whining noise when you start the engine. 
  • Overheating or smoking — If you’ve noticed a smell of smoke in or near the car, it could be a faulty starter motor. The motor may be drawing excess current, causing the smoke. This can be due to an issue with the ignition, a short circuit or running the starter for too long.

  • Oil starter motor — The starter motor’s position in the engine makes it quite susceptible to oil leaks. While leaks in your engine aren’t all that uncommon, if oil gets into your starter motor, it can quickly damage it. 

How to Fix or Replace a Starter Motor

If you notice that your starter motor has an issue, the best thing to do is to get it checked by a qualified mechanic. You can start the vehicle without the starter motor if you can, or call out your roadside assistance if the car doesn’t start. They’ll confirm the problem and either fix or replace the starter motor, depending on the damage. 

Unless you’re qualified, we don’t recommend trying to repair your own starter motor. If you do, get the right tools and equipment to complete the job safely and adequately. 

Need a new starter motor or the right tools for the job? Check out our online store for some brilliant deals on car parts and accessories.

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