The starter motor, or starter motor in some Latin American countries, is an essential component of modern cars. It is responsible for starting the combustion engine in the vast majority of today's vehicles, whether they run on gasoline, diesel, gas, alcohol, or other fuels.
Without an electric starter, we would still have to get out of the car to operate a hand crank on the front , just like with older cars. It wasn't until 1911 that the first car with an electric starter appeared: the 1912 Cadillac. This feature was very well received because it does the work for us, allowing us to start the engine with a simple turn of the key or the push of a button.
The company that developed the starter motor was Delco (Dayton Engineering Laboratories Co.), which supplied this device to General Motors (GM). This company had experience in electrical components, such as the distributor it launched in 1909. So much so that it was more commonly known as the "Delco."
Starter motor operation
Combustion engines work thanks to a self-sustaining cyclical motion within them . However, something has to initiate this cycle, because it cannot do so on its own.
The starter motor runs on electricity , so it's connected to the car battery to receive the 12V that allows it to turn. It also has another wire that connects a relay to the car's ignition switch, which is activated when the key is turned.
As soon as we do this, the relay closes and sends current to a solenoid that pulls a metal bar. This bar is attached to a fork that will push the pinion gear . At the same time, the starter motor will receive current and turn this pinion gear to start the combustion engine via the flywheel . In this way, the engine will begin its intake, compression, power, and exhaust cycle, driven by electricity.
As soon as the engine can complete this process on its own and reaches a certain speed, the starter pinion returns to its original position to avoid interfering with its operation. This process usually occurs when you stop turning the car key or automatically when the engine reaches a certain speed thanks to the Bendix drive.
starter motor types
Depending on the type of engine to be started, the starter motor will need to have more or less power . Starting a small 1.0-liter gasoline engine is not the same as starting a large 3.0-liter diesel engine. In any case, starter motors can be divided into four main types:
According to your voltage
- 6V: which can be found on some motorcycles and very light vehicles.
- 12V: are those found in the vast majority of passenger cars and vehicles of similar capacities.
- 24V: which are typical of heavy vehicles. Although they receive electricity from a 24 V battery or from two 12 V batteries placed in series.
Depending on your stator
- with electromagnets: that only work when current is passed through them.
- With permanent magnets: which can be exposed or covered with metal to intensify their magnetic field. Normally they are ceramic magnets, with which you have to be careful because they are fragile.
According to its type of force multiplier
- No force multiplier: in which the pinion rotates at the same speed as the rotor, because they do not have any gear that varies their speed.
- With force multiplier: in which the pinion rotates at a lower speed because it has gears that reduce the speed of the drive pinion. The result is less speed at the pinion, but more torque at the turn, so you can start heavier engines. In other words, it acts in the same way as a gearbox with a low gear.
According to its drive mechanism
- external solenoid: which are the most frequent and which you can see in the video above.
- internal solenoid: On these starters you won't see two housings, because the solenoid is inside the in-line starter housing. For this reason they do not have a fork that transmits the movement.
- sliding armature: the pinion forms a block with the armature and it is this entire assembly that slides to remove the pinion and start the motor. But that is more frequent in heavy vehicles
Parts of a starter motor
We've already mentioned some of these parts in the description of its operation, but a starter motor actually has a few more. This is mainly because it's essentially an electric motor that runs on direct current and therefore has its own specific components. The parts of a starter motor are:
- drive pinion: It is the part with which the starter motor turns the flywheel, thanks to the fact that it has a toothed edge. It also receives the name of toothed crown or bendix. Although this last name is actually a metonymy that consists of calling it by the name of the Bendix brand that manufactured them.
When the starter motor is not being used, the pinion is retracted so as not to interfere with the flywheel. When we turn the key, the relay levers it out so that it can turn and start the engine. - Stator: Like any electric motor, the starter motor has a stator. That is, the fixed part that interacts electromagnetically with the rotor to make it rotate.
- solenoid or automatic: It is a magnetic circuit similar to an electromagnet that creates the magnetic field that attracts a metal bar. Solenoid: operation and uses in a car.
- Forks: is a seesaw with a shaft in the center. When the solenoid draws the metal bar inside it, this yoke swings and pulls out the pinion gear that will start the motor.
- Dock: retracts the pinion when the solenoid does not act to remove it.
- Brushes: they are the ones that maintain contact with the direct current even if the rotor turns.
- rotor or armature: it is the element that rotates driven by the electromagnetic field and that is attached to the pinion so that it rotates in solidarity with it.
- Housings: they are the ones that protect the starter motor and have the appropriate shapes to fix it where necessary by means of screws.
Starter motor failure and symptoms
When your car won't start, the most common problems are a weak battery or a faulty starter motor . To determine which is the best option, you can use jumper cables . If it starts without issue, the engine is fine and the battery simply isn't powerful enough. You can also test the battery with a multimeter.
If you have already ruled out the battery, there are a number of symptoms that you can detect just by listening carefully:
I turn the key and it does nothing.
If you hear nothing, it means there's a problem with the wiring that powers the starter motor or with the motor itself. Specifically, the power cable, the ground cable, or the relay cable. You can check where the problem is without removing the starter motor using a multimeter.
- Set it to V to Direct Current (DC or DC) to 20V (30V, 40V… depending on multimeter)
- Check the cable that supplies power to the starter motor.: put the negative tip (black) on the negative terminal of the battery and the positive tip (red) on the thick cable that reaches the starter motor.
- They should arrive approximately the same as the battery (more than 12V). If nothing arrives, the connection is broken. That is, this cable is broken or unhooked at some point.
- Check starter motor ground: it is the same operation but with the red tip on the positive terminal of the battery and the black tip on the metal casing of the starter motor. If there is no current, it means that the negative cable that goes to the motor is broken or unpinned.
- Finally check the current relay: put the black lead on terminal 50 of the starter motor and the red lead on the positive terminal of the battery. If when starting the engine it measures 12 V, it is good. If not, the starter motor internal circuit is bad.
- If all is well, the problem is elsewhere in the car ignition systemnot on the starter motor.
Engine cranks too slowly to start
If the battery is fine, but not enough voltage is getting to the starter motor, the problem is in the wiring. With the multimeter it is noticeable, because current does arrive, but less than that supplied by the battery.
- It is best check the battery first putting the test leads on the battery terminals (black on negative terminal and red on positive). This way you will know the voltage that the battery gives exactly because it is a data that you are going to need. For example: 12,7V.
- Then, check the cable going to the starter motor like before. If it gives 0,5 V less than what the battery gives, it means that the cable has too much resistance to electricity. Possibly due to a lot of corrosion in the cable contacts or some other deterioration.
- the same if check the ground to the starter motor as before, it should give at most 0,5 V less. If not, the motor ground wire or its connections are bad.
Starter motor turns on its own (idle)
The problem will be in the engine flywheel coupling system. The starter motor must be disassembled and repaired or replaced with another. If that is your case, do not let it idle too much because it can deteriorate more than it is. It may be because:
- la fork It has broken,
- pinion teeth have parted,
- el free shaft is in poor condition or
- flywheel teeth they have been broken or excessively worn.
Car won't start and goes clack clack
If, on the other hand, you hear a rattling or clicking sound when you turn the ignition key, this means that the starter solenoid is receiving power, but the starter motor itself is not. The starter motor must be removed and either repaired or replaced with a new one.
Price of a starter
Their first-hand price is usually between €120 and €300 . Although these prices can easily fall outside that range. Remember that starting the engine of a small car is not the same as starting the engine of a high-performance sports car. The former might be a small 0.9-liter three-cylinder, while the latter could be a massive 5.0-liter V8.
The price can be much higher if we consider newer starter motors that function as generators and auxiliary motors in some situations. In these cases, the price can easily exceed 800 euros.
where is the starter motor
It's usually located at the bottom of the engine , near the flywheel, which is what it has to rotate to start the engine. For this reason, it's difficult to remove in many models. Many components may need to be disassembled to reach it, if it can't be accessed from below.
To locate it, the best thing to do is consult a video specific to your car or the workshop manual. Most often, you'll have to remove the battery , some hoses, or other parts.
Images – Pete, Phil Benchoff, Michael Sheehan, Alper Çuğun, nzhamstar