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5 ways your starter motor can fail, and what to do about it

5 ways your starter motor can fail, and what to do about it

The starter motor was late to the game in terms of automotive additions. We'd had the car for over twenty years before Cadillac came along and fitted an electric starter to its 1912 model. Prior to this, we started our cars by manually cranking them to life via a handle protruding from the engine.

We liked this new technology, and by the 1920s, pretty much every car was fitted with one from new. And why wouldn’t it be a popular addition? Hand-cranking a car was hard, and, if you didn’t get your arm out of the way fast enough, the crank handle would happily break it for you. Ouch!

The starter motor works in modern cars the same way it did back then, by engaging ring gear mounted to the flywheel. By turning this quickly, the engine can start. It’s simple physics, but of course, it’s still a lot of work. That little motor working through your flywheel has to earn its keep, and when it’s about ready to give up, one of the following four things will happen.

01 Engages but the engine doesn’t turn

Assuming your battery is healthy and fully-charged, if you turn the key only to be greeted by the clunk of the starter engaging but the motor doesn’t turn, it can mean a number of things. The simplest cause of this sort of fault is a loose or corroded electrical connection.

If there is a fault with the internal windings of the starter motor, bad brushes, or other electrical faults, the starter motor may lack the torque to crank the engine. There could also be mechanical issues, like bad bearings inside the starter, or teeth no longer meshing in the starter or ring gear. If you turn the key and hear only a thunk or click…

What should you do?

  • You’ll need to inspect the electrical connections between the starter, battery, earth, and if it is mounted remotely, solenoid. If those are all clean and tight, and none of the cables look to be corroded internally…
  • Remove the starter and test it for proper function off of the engine. A starter that is bad mechanically will make ugly noises when spun up and not attached to anything. If it spins freely when not under load, and all the connections were good on the car, chances are the windings or brushes are bad.

02 Starter turns but doesn’t turn the motor

A starter motor’s pinion gear is not constantly engaging the ring gear on the flywheel. Instead, the starter pushes the smaller gear out to engage with the flywheel with a part called the Bendix, which is not much more than a big electromagnet. It's this that pushed the pinion gear out to engage with the flywheel. If you turn the key and hear just a whirring or grinding…

What should you do?

  • You’ll need to inspect the starter to check several things. The first is whether or not the starter is bolted tightly to the motor or transmission. Bolts can come loose, and it doesn't take much movement to interfere with the gears meshing correctly.
  • Another potential issue could be that the teeth on the starter or the ring gear may be damaged. Often an indicator of this is if the problem only happens occasionally, meaning there are good and bad spots on the gear, and sometimes it doesn’t mesh.
  • Lastly, the Bendix part of the starter can go bad, causing it to not push the smaller gear out with enough force to make it engage fully.

Solution: The starter motor spins, so it still works somewhat. This is typically a mechanical issue. A starter motor specialist should be able to rebuild the unit and replace the worn parts or tired Bendix. If, however, the ring gear on the flywheel is damaged, it’s going to be a gearbox-off job to fix it.

5 ways your starter motor can fail, and what to do about it

03 Starter Motor Stays On

If the starter stays on, and you’ll know because the almighty racket going on, shut the car down straight away if possible – this can sometimes be caused by a stuck solenoid, and the only solution is disconnecting the battery.

This is a severe problem, and if you try and drive the car, you're only going to make things worse. Driving it is going to severely damage the electrical and mechanical elements of the starter system.

What should you do?

  • Shut it down. You’re going to need to remove the starter motor and replace or rebuild it. No matter if it is mechanically jammed, or electrically shorted, the only solution if taking it apart and replacing parts

Solution: As above, take the old one out and inspect it. Replace or seek specialist help. Your Haynes manual will guide you through the removal and refitting process.

04 Nothing happens at all, maybe a slight clicking

Commonly, if you turn the key and get nothing at all, or just a small click, the cause if a dead battery more often than a bad starter. But, if the battery is known good, or even with a jump start it doesn’t crank, it could be a starter problem. If nothing at all happens when you turn the key…

What should you do?

  • Use a test light or multimeter and test for power from the ignition switch to the solenoid and starter when you turn the key. Some cars also have fuses or relays that should be tested as well to find the break in the chain of command from switch to starter.
  • All cars have a safety interlock, whether to make sure the clutch is disengaged, or the shifter is in park or neutral. Check that this switch is sending power through it as well.
  • Tap on the starter with a spanner or small hammer as someone turns the key. Oddly enough, this old standby still can work when there is a minor issue jamming things up in the Bendix or solenoid.

Solution: Clean the connections or replace any switches or relays that are bad. If a rap from a hammer solves things, it is time to rebuild or replace the starter.

05 Sporadic Starting

Does your car start fine some of the time, but fail other times? Assuming again that you know your battery is in good health, this can only really be one thing, and that’s the starter motor or solenoid.

The solenoid either sends full current to the starter, or it doesn’t, and something as minor as expansion due to engine heat can make it temporarily fail – some models are notorious for this. Sporadic issues can also be caused by one bad internal winding internally, or a bad spot on the starter's commutator. Intermittent problems seldom get better and often get worse…

What should you do?

  • Check all the external connections for loose wires and plugs, including fuses and external relays.
  • Removing the starter solenoid relay is actually quite simple. However, consult with your Haynes manual first, as you'll need to disconnect the battery in order to remove it without giving yourself a shock. Some are simple, like big fuses. Others bolt-on and are more complicated to remove.

Solution: You can’t fix a faulty relay, so it's merely a case of buying a new one and fitting it. In some applications, this will be as easy as changing a fuse, in others, you may need to get the spanners out. But even so, it's usually a quick job. Your Haynes manual will have all the details for you.

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