Starter Motor

Starter motors is another essential part of a car.  A starter motor's job is to basically turn over the engine to start it up.  You can imagine how hard it is to do this, If you've ever tried turning an engine by hand, it is very hard.  A starter motor is basically an electric motor with a solenoid attached to it. The motor has a very small gear, usually has less than around 10 teeth on it,  and this gear connects to the flywheel/flexi plate and turns it.  The difference in size of the pinion gear and the flywheel/flexi plate is a huge difference,  which gives the starter motor enough torque power to crank the engine.

1.       Housing (yoke)

2.       Overrunning clutch

3.       armature

4.       field coils

5.       brushes

6.       solenoid

 Armature

 Solenoid

 Housing (notice the bushings inside)

 Armature sitting in yoke

 This was a unique to all the other motors,  it seems to have some different type of bearing inside.  Instead of bearings, it had three gears that moved around the armature to let it rotate freely.  This whole piece inside the housing moves up and down as the solenoid does.

 Brushes. notice the terminals to positive. The other two are connected to the housing which is ground.

 Brushes

 Armature

 Coils

Solenoid connected to housing.  notice the lever connected to the solenoid.  This rocks back and forth to move the armature.

The housing (or yoke) is the main enclosure of the motor, it holds the motor itself and the solenoid together.  It also holds all the terminals.

The overrunning clutch is a type of clutch similar to the clutch on your bicycle.  Once the starter motor has done its job and has started the engine,  the flywheel is still connected to the pinion gear.  This means that when the pinion gear and flywheel are connected, the pinion gear can rotate freely while the engine is running.  The clutch allows the pinion gear to rotate the pinion gear without rotating the motor itself.

The armature is the rotor built of coils inside and magnets.   This armature is powered with electrical current and the electro-magnetic force of the armature and the field coils causes it to rotate.

Field coils are the coils and magnets that work with the armature to rotate it.  This is also powered with an electric charge.

Brushes are similar to the brushes on an alternator.  They are designed to contact the terminals that don't move to the rotating armature inside.   They are basically like buttons that are tensioned onto the armature by springs.

The solenoid is a very common electrical component in a vehicle,  it's basic job is to convert an electrical energy into mechanical energy.  The starter motor has a fairly large solenoid,  It works simply by when the key is turned to start, the solenoid is powered building a magnetic field,  This magnetic field moves the armature back and forth via a lever that pushes it like a sea saw.  The solenoid's positive terminal is also connected to the motor's positive terminal.  The housing of the starter motor acts as negative (grounding).

Here is what is roughly looks like when assembled:

[diagram]

What are the repairing procedures of diagnosing a starter motor?  First of all, the starter motor is usually located near the fly wheel, which is usually between the engine and transmission.  It is in most cases very hard to get to, so be very careful when working on them.

The basic rule when diagnosing starting problems is list your car's symptoms.  In this case, If the starter motor seems to be cranking the engine over,  obviously, the starter motor works fine, something else is your problem.   Before you go working on the starter motor, make sure the battery is charged and in my words,  check the "fire triangle".  (engine needs a spark, fuel, and air to work.  This means check that the distribution system and sparking system works, and also the fuelling system.  Obviously make sure there is fuel in the car.)  Also check alarm systems that they have not malfunctioned.

When you are convinced that your starter motor is definitely the problem, as  usual, perform a visual check.  Since we can't see much with a starter motor, just check that terminals leading to the starter is neat and tidy.  Check that all connections are neat and don't have corrosion.  Check that the cables aren't being tensioned,  insulations haven't melted or come off, etc.   If the car has fusible cables,   make sure those fuses haven't blown.  Also inspect for anything like starter relays, which are relay switches that are in the starter circuit, which can be found in cables that run along to the starter form the battery.

Check for voltage drops.  Disable ignition system before you do this, so that the engine doesn't start while cranking the engine over.  the Using a multi-meter, set to volts D/C, and select appropriate range.  Remove the key from the ignition, and connect positive pin on battery negative, and positive pin on the starter motor terminal.   Turn key to crank position.  You should get a reading of around12-13V (depending on vehicle model).  If the starter motor is hard to reach, perform a negative voltage drop. 

Starter motors don't usually have mechanical failures, but if the car is that old, and you suspect that something in the starter has worn out,   The bushings may be worn out and are losing contact with the armature.