Starting Systems

State a major safety precaution when removing or working around a starting motor

Don’t make your starter an Arc Welder!

Always unhook the battery ground

Before removing the starter motor

Starting Systems

Identify the following components

Armature

Commutator

Brushes

Pole Shoe

Field Coil

Starter Armatures

The Armature is a rotating electromagnet

Commutator bars allow current in and out of the armature

Brushes ride on commutator barsBrushes transfer electrons from the stationary field coils to the spinning armature

Insulated BrushesGrounded Brushes

Field Coils are Stationary Electromagnets

Pole Shoes concentrate the stationary magnetic field

Starting Systems

Identify the following components

Starter housing or frame

Bushings

Starter Drive Pinion

Over-running clutch

Starter Diagnosis

Worn out bushings...Allow the armature to drag on the pole shoes

This will slow the starter and INCREASE amp draw

Worn or Dry Armature shaft will

INCREASE amp flow

Burned commutator bars restrict the amp flow

Worn out brushes DECREASE amp flow

There will be more questions...

...On the test….

…than I am covering here.

Read your book…

and complete Starter Labs

Test the Starting System

Check Cranking RPM

Check Cranking Volts

Check Cranking Amps

Low Cranking RPM

A slow turning starter will pull extra amps

Could be caused by tight engine

(New Engines)

Can be caused by advanced timing

Low Cranking RPM

Low cranking RPM….

…With low cranking Amps…

Bad Starter

Worn brushes, Bad commutator bars, open in field or armature

Cranking Volts

Power is required to turn motor

P = I x E

Low volts will cause high amps

Low Cranking Volts

Cranking volts at battery should be over 10V

Load test battery if low cranking volts

Excessive amp draw can cause low cranking volts in a good battery

High Cranking Amps

Check voltage drop across STARTER MOTOR

If Battery cranking volt is 1/2 volt more than Starter volt drop diagnose battery cables and connections

If cranking volts are within 1 volt of battery…

Insure engine turns freely

Insure ignition does not cause slow turning engine

Replace Starter Motor

(assuming there are excessive amps)

Before you install the rebuilt starter

Bench test the replacement

It may save you a starter R & R

Starting Systems

Understand the operation of the two starting circuits

#1 Starter Control Circuit

#2 Starter Motor Circuit

Starter Solenoid

Understand the function of the Pull In solenoid windings….

…and the hold in solenoid windings

Starter Solenoids

Predict the effect of an open circuit in the solenoid pull in windings….

….and the solenoid hold in windings

Notice pitted contact ring

24 Volt Series/Parallel Switch

Understand how 12 volt batteries can be used to run a 24 Volt starting system

Series/Parallel Switch

Diagnose a defective series parallel switch using a volt meter

Starter Control

Identify variations in starter control circuits

Test the Starting System

The Bottom Line Test cranking RPM

Test Cranking Volts

Test Cranking Amps