Internal combustion engines cannot start themselves; they require input from an external source of energy in order to get going. This starting process may be electrical, hydraulic, or pneumatic, depending on your preference.

In most vehicles, this function is carried out by electric motors, which are more commonly referred to as starters or starter motors. Because of its strong starting torque, the DC series motor is an excellent choice for use as a starter motor. This is because it is necessary to overcome significant levels of friction and compression resistance during the starting process.

Your electric starter motor engages when you turn the ignition to “run.” The starter turns the engine over allowing it to suck in air. 

On the engine, there is a flex plate or flywheel, with a ring gear around the edge, that 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 or Bendix drive).

When you turn the ignition switch, the starter motor is energized, and the electromagnet inside the starter motor body engages. This pushes out a rod to which the pinion gear is attached. The gear meets the flywheel, and the starter turns. This in turn 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!

Symptoms Of A Faulty Starter

A faulty starter motor can exhibit several symptoms, but the four main ones to look out for are:

• No Cranking Sound: When you turn the key or press the ignition button, the starter motor should engage with a distinct cranking sound. If you hear no noise at all when trying to start your vehicle, it could indicate a faulty starter motor.
  

• Clicking Sound: If you hear a rapid clicking sound when you attempt to start your vehicle, it might be a sign of a faulty starter motor. This noise often occurs when the starter motor isn't receiving enough electrical current to turn the engine over.

• Slow Cranking: If the engine cranks very slowly when you try to start it, it could be due to a weak or failing starter motor. Slow cranking can be a result of various issues, including a weak battery or a worn-out starter motor.

• Intermittent Starting: Sometimes, a faulty starter motor may work intermittently. Your vehicle might start fine on one occasion and then refuse to start on another. This inconsistency can be frustrating and is often a sign that the starter motor is failing.
  

Causes Of A Faulty Starter Motor

The main causes of the symptoms associated with a faulty starter motor include:

• Worn Brushes: Inside the starter motor, there are brushes that make electrical contact with the armature (a rotating coil). Over time, these brushes can wear down, leading to poor electrical connectivity and reduced motor performance. This can result in slow cranking, clicking sounds, or intermittent starting.

• Faulty Solenoid: The starter solenoid is responsible for engaging the starter motor with the flywheel or flexplate. If the solenoid fails, it may not transmit enough electrical current to the starter motor, leading to clicking sounds or a complete lack of cranking.

• Worn Armature: The armature is a critical component of the starter motor that rotates and engages with the engine's flywheel. Over time, the armature can wear down or develop faults, causing the starter motor to struggle or fail to engage properly.

• Corrosion or Poor Electrical Connections: Corrosion or poor electrical connections at the battery terminals, starter motor terminals, or ground connections can inhibit the flow of electrical current to the starter motor. This can result in slow cranking or a failure to start.

• Weak Battery: A weak or discharged battery may not provide sufficient electrical power to the starter motor. This can lead to slow cranking or a clicking sound when attempting to start the vehicle.

• Ignition Switch Issues: Problems with the ignition switch, such as worn contacts or electrical faults, can prevent the starter motor from receiving the necessary signal to engage. This can result in a lack of cranking.

• Starter Motor Wear and Tear: Like any mechanical component, starter motors can simply wear out over time. The internal components may become worn, leading to decreased performance and eventual failure.

Testing The Starter Motor

Overloads are the main reason for electrical problems with the starter. This may show up as ground and winding short circuits in the field and armature winding, but it may also appear in the control element coils (solenoid switch) on occasion. 

High loads are placed on carbon brushes and collectors, which makes them more prone to problems than the alternator. Clamping carbon brushes in the starter, for instance, results in the production of considerable arcs because of the high currents, whereas clamping carbon brushes in the alternator does not cause voltage to arise and thereby relieve the alternator. Frequently, these arcs damage or destroy the collector. For troubleshooting, a multimeter and a clip-on ammeter are necessary. However, acoustic perception can also be used to find fault sites (like the pinion).