Everything you need to know about Starter Motors
Few things are as easy as starting the modern car. Turn the key or press the “Start” button and you're on your way. Until, one morning the engine doesn't turn over.
Suspicion usually falls first on the battery, but there's another part of the car that could be at fault: the starter motor. Starter motor problems are often mistaken for battery problems. It's not unusual for owners to spend time and money fixing a battery problem, only to find out the fault lay with the starter. That's why it pays to understand the basics.
How it works
A starter motor consists of a small gearwheel, termed the pinion, mounted on the end of a shaft. That shaft is at the center of an electric motor. Turning the ignition key lets current from the battery flow through the motor windings which makes the the shaft spin.
At the same time, the pinion is pushed forward on the shaft so it can engage with teeth on the flywheel. In most starters that push is provided by an electric device known as a solenoid. This too is activated by turning the ignition key. (In older starters the pinion is keyed to a spiral groove in the shaft which throws the gearwheel forward as it turns.)
The flywheel, a large metal disc mounted on the end of the crankshaft, has two jobs. One is to smooth out vibration and help the engine maintain its speed when the gas pedal is released. The other is to be the large gearwheel that the starter turns.
Turning the ignition key engages the pinion with teeth around the edge of the flywheel and starts the engine rotating. This causes one of the pistons to move up and compress the fuel-air mixture, where a spark makes it burn rapidly, pushing the piston back down. From this point the engine will keep running; the starter is no longer needed, and the driver releases the key. The solenoid then pulls the pinion back away from the flywheel and current stops flowing from the starter motor. It's work is done.
Recognizing starter problems.
Starter motors are very reliable, but like everything, they wear out. It's usual to get 60,000 miles or more from a starter, depending on how many starts it endures, but eventually it will need replacing. Sometimes a starter will let you know when it's going bad by making grinding or crunching noises. More often though, it appears all is well until one morning it refuses to turn.
Diagnosis begins by verifying that the battery is good. See if the headlights will come on. If they seem bright, that says there's some juice in the battery. If not, start by getting the battery recharged (or jump starting the vehicle.)
If you're confident the battery is in good shape, listen for a clicking as the ignition key is turned. That's the sound of the solenoid working: if you don't hear it there may be a problem with the electrical connections at the battery. Check that the terminals are tight. Then, if there are no obvious electrical issues, it's time to look at the starter.
Some auto parts stores have equipment to test a starter. The problem is, that means removing it from the vehicle first. It's not especially difficult for a competent amateur mechanic, but starter motors are heavy and generally have to be reached from underneath. You may well decide this is best handled by a professional.
Modern starter motors rarely go wrong. What may appear to be a starter problem is more often a battery or electrical fault. Check those out first before blaming the starter!
