11 Parts Of Car Starter Motor And Function

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Starter motor components – engine starting system is a system that have a function to crank the engine for the first time. The working principle of starter motor is to rotate the engine crankshaft via flywheel using electric motor circuit. The result is a rotating crank and engine cycle can be triggered to work continuously.

In this article, we will learn all about parts of starter motor and their function. Check the article below.

All Parts Of Starter Motor and function


part of starter motor and their function
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1. Solenoid starter

The first component you can see on the part that looks like a small tubular part on the main motor. This component is named solenoid starter because it contains two solenoid. The main function of Solenoid starter is to push the pinnion drive gear and give voltage on main motor.

There are two solenoid in this component namely;
  • Pull in coil, this component works to push the plunger to push the drive pinion gear.
  • Hold in coil, is a similar component located in front of the pull in coil. Its function is to withstand the movement of the pull in coil and connect the battery current to the main motor.


The shape of the solenoid is like a coil, where an iron core is placed in the middle of a copper coil. But this winding has a large number and the dimensions are also larger so as to move the plunger with a strong and fast.

2. Solenoid plunger

the motor starter function pdf

The plunger is located at the end of the pull in coil. Its function is only one that connects the movement of pull in coil to drive lever. In other words, this component only acts as a connecting rod. However, this plunger material is also strong because it will connect the pull in coil pull that have strong movement.

3. Solenoid cap

The solenoid lid is a starter solenoid cover circuit located on the front of the starter. Not only as a cover, but this part is also used as a media liaison between the current from the system to the starter actuator. Actually there are 3 pieces of terminal on the starter motor ie
  • Terminal 50, is a terminal connected to the starter circuit of the ignition key. Through this terminal the starter motor gets the command to active or not. When terminal 50 gets current then the solenoid will work and the starter will react.
  • Terminal 30, the terminal which directly gets the electric current from the battery. In other words electric current is always available at this terminal when the motor is off or on.
  • Terminal C, the terminal used to channel the main currents from the solenoid to the starter motor in order to rotate. It  will connect the current from terminal 30 when terminal 50 gets current.


4. Field Coil

We go to inside the motor starter, here there are many components that you can find. First you can find the field coil. What is a field coil? field coil is a series of magnetic coils used to generate magnetism around the coil rotor. According to the working principle of an electric motor that requires a magnetic field around the rotor, this component will provide it.

But the coil field is not a permanent magnet, the field coil will only generate a magnet if there is a current input from terminal 50. This process we usually call the process of electromagnetic induction. The field coil is also consists of several parts such as
Yoke, is the housing where the coil is located. In this case the coil lies inside the yoke.
Pole core, is a flat iron core which is used as a place of welding of copper to become a coil.
This coil is made of ordinary copper coils make with a certain direction around the pole core, in the yoke there are about 4 to 6 units of pole cores are interconnected to obtain great magnetism.

5. Armature coil

The next component, inside of starter motor, it is commonly referred to as a coil rotor or coil located around the motor shaft. The main function of the armature coil is also as a magnetic field generator that will be reacted with magnet field coil for the occurrence of movement.

The shape of armature coil such as rotor that hav tubular shape. In general it is coated by copper, the difference with field coil, can be find in its dimmension and amount of coopers. Armature coil has a large number of windings and the amount of coopers also quite large, so the diameter of the coil is also larger.

6. Commutators

type of starter motor
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The next component, located on the front of the armature coil, it shaped like a segmented copper plate. The function of the commutator is to connect the electrical current from the brush to the armature coil. The segmented form of commutator prevents short circuiting of electric current because in the process the commutator will be connected to positive and negative currents directly.

7. Drive lever / Actuator shaft

We go back into the solenoid, here there is a fork-shaped component that serves to move the pinion gear. The drive lever works with the principle of the lever, which will bring up the pinion gear when the other end is pushed in opposite directions. Who is pushing? this is a function of pull in coil through plunger. While the other end will make the pinion gear pushed out and connected with flywheel.

8. Brushes

The next component lies on the main motor. Here is a series of brushes used to connect the electrical current from a static conductor to a dynamic conductor. That is, this brush will send an electric current from terminal 50 to the armature coil that moves around through the commutator.

In a starter motor, there are usually about 4 or more brushes with two as a positive brush and the other two as negative brushes. The material of this brush is also made of copper but softer, to keep the commutator from wearing out. But, the impact brush become more quickly wear out. If this happens then the starter will be difficult to run.

9. Drive Pinnion Clutch

The next component, we will encounter a mechanical clutch that has function to connecting and disconnecting rotation from the starter shaft to the flywheel. Why the rotation need to be disconnected? it is because the stater motor is unlikely to keep working when the engine is running. So in a normal condition, the starter will be connected and when the starter system is turned on the round starter will be connected with flywheel.

How to work this clutch that is by utilizing slide gear with tilt model. this is because there is an overlap clutch component located at the end of the pinion drive. When the starter system is turned on then the drive lever will push this clutch, but with the angled slide gear then the pinion drive will move out while rotating beyond the starter spin.

This is intended for pinion to be fast and perfect timming connection with a flywheel gear. In the reduction strater type, this coupling component gets an additional part that is used as a rotary reducing gear, the goal is that moment on pinnion gear becomes bigger.

10. Drive pinnion gear

The next component is shaped like a gear in general that is located at the end of the drive pinion shaft. The function of this pinnion gear is to connect the rotation of the generated electric motor to the engine crankshaft via flywheel. The pinnion diameter is quite small compared to the flywheel so it will increase the gear ratio that makes the starter system capable to rotate high capacity engine.

11. Motor housing

components of starter motor and its function


The last part is housing, which has the function as a protective part and as a place to put various components of starter. This housing is made of metal consisting of tubular main housing, pinion housing as pinion gear and stamped in front of the main housing as a starter chassis cover.


Thus the full article and clear about the parts of the starter motor and their functions on cars and motorcycles. Hope can increase our insight and benefit us all.