Under the hood of your car lie the most essential components, which include the starter motor. If you look more closely, often at the bottom rear of the engine, you’ll see this unmistakable cylindrical component. Its function? Crank the engine every time you turn your key or press that ignition button on your steering wheel or center console.
Like any other car component, your starter motor also breaks down over time. Most of the time, it’s the wearing of its component that causes such malfunctions. This guide lists the starter motor components. Use this as a reference to understand the part’s build and diagnose any issue should ignition troubles start bothering you.
Parts of the Starter Motor
At first glance, a starter motor may not seem complex. Besides the fact that it has only one job of cranking the engine, it’s also physically small and only runs for a few seconds. But don’t be fooled by its appearance. Inside are several components that work in tandem with one another. Open the starter’s housing, and you’ll see a rather intricate system any non-mechanic will find difficult to decipher. Here are those starter motor parts:
1. Armature
Taking up the biggest internal space of the starter motor is the armature. It’s the starter’s rotating core, consisting of the shaft and laminated iron core wrapped by the copper windings. It’s responsible for creating a rotational torque that rotates the shaft and turns the engine’s flywheel.
2. Commutator
The electrical current and magnetic field inside the starter motor aren’t enough to spin its armature. There needs to be a reversal of the current in the copper windings every half-turn. Otherwise, the magnetic forces within the motor will cancel each other out, resulting in no movement. This is the primary job of the commutator. It’s that small copper cylinder connected to the end of the armature shaft.
From the outside, it resembles a copper ring with lines or grooves around it. It’s not very big, measuring only a couple of inches across in most car starter motors. It’s also where the brushes press against to pass electricity into the spinning part of the motor.
3. Brushes
Disassembling a 12V starter motor reveals four small blocks that gently touch the commutator. These are the brushes with two negative and two positive blocks. Their purpose? To deliver the needed electrical current through the commutator to rotate the armature. They’re spring-loaded to maintain constant contact with the armature, delivering uninterrupted current flow even when the motor is spinning.
4. Field Coils / Permanent Magnets
Inside the starter’s metal casing, wrapped around the armature, are either thick wire coils or strong permanent magnets. They create the magnetic field that the armature needs to spin. Older starters use wire coils that resemble thick copper loops, while newer ones feature solid magnets that remain in place.
5. Solenoid
If you go around and look at most modern starter motors, you’ll notice there’s a uniformity among their build. They often come with two-cylinder sections. The larger cylinder houses the armature, while the smaller, secondary one is the solenoid. This part acts as an electromechanical switch that does two things. One, it pushes the pinion gear forward, allowing it to connect with the engine’s flywheel. The gear automatically retracts once the engine is turned over.
Two, it closes a high-current circuit that allows power to flow directly from the battery to the starter motor. This is necessary to concentrate the power as the starter motor uses a lot of it during the ignition process.
6. Plunger (inside solenoid)
Break apart a solenoid, and you’ll see its working mechanism. Inside is the plunger. It’s that smooth metal rod similar in size to a short bolt. What it does is move back and forth every time the coil is energized. Once you turn your key, the plunger shoves the pinion gear forward to engage with the flywheel.
7. Pinion Gear
Then there’s the pinion gear, also called the drive gear. It’s that small, rugged-looking metal gear with thick, spiral or straight-cut teeth. It’s responsible for meshing with the flywheel, directly cranking the engine, and disengaging automatically once the ignition is complete.
8. Overrunning Clutch (One-Way Clutch)
This clever piece sits between the pinion gear and the armature shaft. It lets the pinion spin the engine’s flywheel but stops the flywheel from spinning the starter motor too fast once the engine’s running. Without it, the starter could get damaged fast.
9. Shift Fork
This small metal lever may not look like much, but engine ignition wouldn’t be possible without it. Sitting between the plunger and the shaft, this trusty part is the pinion gear’s compass. When the solenoid activates, the plunger pulls the shift fork, guiding the successful engagement of the drive gear and the flywheel. It’s that distinctly U-shaped metal arm in the starter motor.
10. Starter Housing
Of course, there is the most visible and largest part of the starter motor components. The starter housing is what you’ll see from the outside, encasing the whole mechanism and internal components of the motor. It may not be flashy under the hood, but it’s sturdy enough to keep every component protected.
Conclusion
A starter motor, on average, can give you a valuable 7-10 years of service. Of course, early breakdowns are always a possibility. However, with proper maintenance and timely repair, you can always make the most out of this critical under-the-hood component.
Familiarizing yourself with its components is the first step to understanding the early issues with your starter motor. Bookmark this guide to have a handy reference in diagnosing your starter motor parts.