How a Starter Motor Works

Video demonstration on how a starter motor works. This is a full in depth video explaining the operation of a starter motor along with a few different demonstrations, but does not cover how an electric motor works. Understanding how a starter motor assembly works will also help troubleshoot a faulty starter motor. This particular video was done on a starter which was removed from a Ford Ranger for rebuild purposes.

Explanation:
-a starter is a small electrical motor and solenoid assembly intended to turn an engine over
-the starter is generally located toward the bottom of the engine connected to the bell housing of the transmission, but this can vary between designs
-the motor is a device while is able to turn electricity into a mechanical force
-the solenoid acts similar to a relay, where it controls a high average circuit using low average
it also acts as an actuator to engage a mechanical device which is the pinion gear
-the ignition switch which is the main controller of the circuit
-the battery that provides the power enable both the motor and solenoid to power up
-the ignition switch and solenoid both operate on the low amperage circuit
-the starter operates on the high amperage circuit and the case of the starter motor assembly is ground or earth
-when the ignition switch is turned to the start position, this activates the solenoid that provides mechanical movement and in turn turns on the high amperage circuit providing power to the motor and the motor then rotates
-once the spring loaded start position is deactivated, everything pulls back into it’s neutral position
-the solenoid works on an electro magnetic field which pulls in the plunger
-once that plunger hits the end of it’s travel a contact inside engages turning on the high amperage circuit that operates the starter motor
-the movement of the plunger operates a level that pushes out the pinion gear
-the final drive is what gives the starter motor it’s torque so it’s able to have enough power output to turn over the engine
-designs will vary between starter designs so not all will look like this, but will have some similarities
-there is a planetary gear set in the final drive assembly which gives roughly a 5:1 gear reduction in the final drive
-pinion gear is what drives the ring gear on the flywheel so the engine can turn over
-there is an overdrive clutch which that for torque in only one direction and freewheel in the other direction
-if the pinion gear were to jam in place with the flywheel, then this feature will prevent it from overspeeding which would cause damage to the starter
-there is a helix which is a machined screw type groove that enables the pinion gear to slightly rotate just before the starter motor is powered up and turns
-this rotation is needed to allow to pinion gear mesh into the ring gear

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[ChueyMr]

When I energize the solinoid on my starter the motor slowly rotates. I can't get the solinoid
to activate with no motor action. Whats wrong with my starter?