When you turn the key in your car’s ignition, the engine turns over and then cranks. However, getting it to crank is actually much more involved than you might think. It requires a flow of air into the engine, which can only be achieved by creating suction (the engine does this when it turns over). If your engine isn’t turning, there’s no air. No air means that fuel can’t combust. The starter motor is responsible for turning the engine over during ignition and allowing everything else to happen.
How your starter works
Your starter is really an electric motor. It engages when you turn the ignition to “run” and turns the engine over allowing it to suck in air. On the engine, a flexplate or flywheel, with a ring gear around the edge, is attached to the end of the crankshaft. On the starter, there’s a gear designed to fit into the grooves of the ring gear (the starter gear is called a pinion gear).
When you turn the ignition switch, the starter motor is energized, and the electromagnet inside the body engages. This pushes out a rod to which the pinion gear is attached. The gear meets the flywheel, and the starter turns. This spins the engine over, sucking in air (as well as fuel). At the same time, electricity is sent through the spark plug wires to the plugs, igniting the fuel in the combustion chamber.
As the engine turns over, the starter disengages, and the electromagnet stops. The rod retracts into the starter once more, taking the pinion gear out of contact with the flywheel and preventing damage. If the pinion gear remained in contact with the flywheel, it’s possible that the engine would spin the starter too fast, causing damage to it.
This article originally appeared on YourMechanic.com as How Does a Starter Motor Work? and was authored by Valerie Johnston.