Starter Motor Parts, Types, & Functions

Starter motors are essential starting system components to start your baby ride. Without it, your vehicle will not start. It is controlled electronically to start the internal combustion engine. Since the engine cannot make the first rotation cycle, the starter motor spins the flywheel, which spins the engine crankshaft to start the engine.

Once the engine starts, the starter motor lets the engine crankshaft and the flywheel do their thing – to keep the engine running. The following sections will discuss starter motor parts, types, and functions. But first, what is the function of a starter motor, anyway?

starter motor parts diagram

What is Starter Motor?

The starter motor is an electronic device that rotates the engine crankshaft when you turn the ignition key. Once the internal combustion engine starts, the starter motor disconnects from the engine and lets the combustion cycle drive the engine. The starter motor is located at the engine and transmission meeting point and connected to the flywheel teeth.

As an electronic device, the starter motor has a direct current (DC) motor and a solenoid. The solenoids receive electric flow from a 12-volt battery to rotate the flywheel. This means you must have a charged battery to power the device. Most times, when you turn the ignition key and the engine cranks without starting, the starter motor or the car battery is the culprit.

The primary function of the starter motor is to rotate the engine until it starts. Aside from this single function, the component is useless. However, this singular function is critical to every internal combustion engine because the car will not start without it.

Like other car system components, the starter motor can fail and give one or more lousy starter motor signs to notify the driver to contact a mechanic to check and rectify the fault.

However, since the system consists of several parts, a malfunction may mean one or more of these parts are bad. We’ll explain starter motor parts and functions to help you figure out when they fail. But before that, let’s see the types of starter motors.

starter motor parts suppliers

Types of Starter motors

There are different types of starter motors. Let’s see how they work.

Direct drive starter motor

Direct drive is the most common and oldest type of starter motor. It has different construction designs and applications, but a solenoid is a mechanical unit. However, it works like the other types.

The solenoid receives an electric flow when you turn the ignition key or press the power button on cars with keyless features. The electric flow pushes the plunger to shift the lever that moves the pinion gear. In turn, the pinion gear meshes the flywheel teeth. Therefore, as you crank the engine, the starter receives power and spins along with the flywheel, enabling the engine to start.

Planetary gear

This type of starter motor has greatly replaced the direct drive starter motor. This type has a permanent magnet to send electric flow between the armature and pinion shaft. As a result, the armature rotates with more torque and speed.

The planetary gear has a significant amount of gear reduction and reduces the need for high electric current. This type of gear has three stationary plenary gears inside the ring gear and a sun gear at the end of the armature.

Permanent magnet gear reduction

This type has less weight, generates less heat, and has an easy construction design. A permanent magnet gear reduction starter has no field coils, but it has four to six magnet field assemblies and three terminals on the solenoid. The brushes and commutators transmit electric flow to the armature directly since it has no field coils.

Permanent magnet direct drive

The permanent magnet direct drive motor functions like the direct drive starter motor. The only difference is that the field coil in a direct drive is replaced with a permanent magnet.

Off-set gear reduction

The off-set gear reduction spins with high speed under low electric flow. They are primarily seen in four-wheel drive because they enhance cranking torque. They also have light and compact designs, making them easy to assemble.

Inertial starter motors

This type of starter motor is an electric motor with all the functions of the other types. It starts the engine fast and strong. However, the inertial starter motor has a lesser torque capacity with the best cranking speed.

What does the starter Motor look like?

The starter motor is a twin cylindrical motor that rotates the engine crankshaft to start the car. One of the cylindrical units is bigger than the other one. The smaller one is the starter solenoid, while the bigger unit is the starter motor.

The smaller unit, the solenoid, has two to three electrical terminals. One of the terminals is connected to the bigger motor, while the others connect to the car’s electrical system and battery.

Starter motor parts and their Functions

We explained earlier that the starter motor determines whether your car will start or not since it initiates the engine crankshaft rotation. A single-unit component cannot do this on its own. So, the starter motor consists of several parts. Here is a starter motor part list with brief descriptions.


The armature is an internal starter motor component. It is an electromagnet unit that supports bearings and is mounted on the drive shaft. It is made of a laminated iron core and consists of windings and commutators. You cannot see this component unless you disassemble the starter motor.


A commutator is a part of the rear end of the housing that the brushes drive on to conduct electric flow. It consists of two plates that are attached to the armature. These plates transmit electric flow to the electromagnetic coils.


The brushes travel across the commutator areas at the rear end of the housing. It contacts the commutators and conducts electric flow.


The solenoid is the smaller cylindrical tube attached to the starter motor (the bigger unit). The solenoid has two terminals, and its function is to push the pinion drive gear and transmit current to the main motor.

Solenoid plunger

The solenoid plunger is at the end of the pull in a coil. It acts as a connecting rod that connects the movement of the pull in a coil to the drive lever.

Solenoid cap

This is the solenoid lid circuit installed on the front of the starter. This part is not just a cover; it helps transmit electricity from the car battery to the starter actuator.

Field coils

Field coils are internal starter motor system components. They are a series of magnetic coils that generate magnetism around the coil rotors. It works with the electromagnetic induction principle. It is worth noting that field coils are not the same as permanent magnets. So, you’ll not see this component in permanent magnet starter motors.

Drive lever

The drive lever is an internal component inside the solenoid. It has a folk-shaped design that moves the pinion gear. The drive lever brings up the pinion gear when the plunger pushes the other end in the opposite direction.

Drive pinion clutch

This internal clutch mechanism component connects and disconnects the starter from the engine flywheel. It disconnects the starter motor from the flywheel because the starter is not needed once the engine starts running.

Starter housing

This is simply the protective cover that houses other parts. This part is made with metal material, consisting of the cylindrical housing and the stamped end of the pinion gear that connects with the flywheel teeth.

Final Words

We have explained starter motor parts and how they work. We’ve also seen different types of engine starter motors. The primary function of the starter is to rotate and start the engine. Unfortunately, this component can fail over time, preventing the engine from starting.

But before this happens, it’ll give some bad starter motor symptoms to notify you to check the system. If the component fails and you choose to replace it, you can search for “starter motor parts near me” to buy it from a nearby starter motor parts supplier around your hood. You can also order it online or have your local mechanic rectify the issue.


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