Understanding the basic principles of how your car works can be really helpful. Without a starter motor, your car quite simply would not start so it’s good to be aware of the simple mechanisms involved.
What does a starter motor do?
Located near the transmission in a car, a starter motor is responsible for starting a vehicle. It is placed near the transmission as it needs to extend a starter gear into a flywheel (a toothed gear attached to the back of the engine).
What are the key parts of a starter engine?
The main parts are the starter itself and the starter solenoid. A solenoid (an arrangement where a switch turns on an electromagnet to complete a circuit) is required as the switch must be turned on and off as quickly as possible to prevent sparking.
The solenoid is usually on the starter although it can sometimes be on the fender wall. There will be a red power wire attached to the starter solenoid. This power wire (protected by the starter relay) runs between the battery and the starter solenoid. The power wire carries the heavy electric current from the battery to the starter – this high current requires a large switch to handle it.
What’s involved in a starter motor?
To get a motor to start, it has to be turned at speed – allowing the cylinders to take in fuel and air, which they will then compress. The starter motor plays this role – it rotates the engine in order to start the combustion process.
The electric starter motor has a shaft with a small gear wheel (sometimes called a pinion). There is also a flex plate or flywheel bolted to the rear of the crank shaft. The gear wheel engages with a larger gear ring around the rim of the engine flywheel. It’s important to remember that a starter is not engaged all of the time.
The other key component to a starter motor is a device called a Bendix gear. This engages its pinion with the gear ring on the flywheel – but only while the starter is turning the engine. When the engine picks up speed, the Bendix gear will disengage – either by the inertia system or the pre-engaged system.
So what engages a starter motor in the first place?
The starter switch is generally worked by the ignition key. It engages when the key is turned to a start position, thus completing a circuit. Generally, an ignition switch has a return spring which ensures that once the key is released, it will spring back and turn the starter switch off.
Does the starter motor stay engaged?
No, and in fact it’s important that the starter motor only turns enough in order to start the engine. It uses a large amount of electricity therefore can quickly run down the battery of a car if left engaged. Equally, the bendix will be activated if the ignition key is turned when the car is already running which will then push the starter gear into the flywheel, which will already be turning. This can cause the moving gears to mesh and can break the teeth of the starter gear, as well as causing an unpleasant crunching noise.
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