Watching old movies, and mean really old movies, I’d see a man take a crank from the inside of the car, insert it into the front of the car, and turn the crank. The driver was turning a “watch spring.” Once the watch spring was wound up, he’d get inside the car and release the watch spring. As the watch spring unwound it would turn the engine.
Around 1913 Henry Leland and Charles Kettering developed the electric starter. An obvious improvement over the hand cranking method to start a car.
Electric starters have three parts. An electric motor, a starter gear, and an item referred to as a “Bendix.” Also a flywheel is bolted to the back of your engine. The flywheel has teeth similar to the teeth you see on the back of a bicycle wheel.
Bicycles use a chain to turn the rear wheels. Cars use starter gear which meshes with a flywheel similarly to the way a bicycle chain meshes with the teeth on the rear bicycle wheel.
When you turn your key to the “start” position, 12 volts are sent from the ignition switch to the bendix. This causes the bendix to extend the starter gear so it meshes with the flywheel. At the same time, the bendix starts the flow of electricity from the battery to starter motor. When this happens your engine cranks.
A starter does not cause a car to start; it just causes the engine to “Turn over.”
When you release the key, it bendix causes the starter gear to retract back inside the starter, and stops the flow of electricity from the battery to the starter motor.
A starter needs replacing if the bendix is bad, the starter gear is bad, or the starter motor does not work.
If electricity does not flow from the ignition switch to the bendix, the starter will not turn. This can happened if the ignition switch is bad, or the alarm system on your car has not been ‘turned off.’ Also, a small amount of corrosion at either end of the wire from the battery to the starter motor can prevent the starter motor from turning by reducing the amount of power which flows through this wire.
A discharged battery or a bad battery cannot provide enough power to “turn-over” an engine.
Understanding all this, if your car’s starter does not crank your engine, it does not mean your starter is bad. It means you need to bring your car to a qualified mechanic to have it properly diagnosed.