Manual Drivetrains and Axles Fourth Edition

1
start
2
OBJECTIVES
After studying Chapter 40, the reader should be
able to

• Describe how the cranking circuit works.
• Explain how to disassemble and reassemble a
  starter motor and solenoid.
• Discuss how to test the cranking circuit.
• Describe how to perform cranking system testing
  procedures.

3
KEY TERMS

• ampere-turns armaturebench testing
  brush-end housing brushes
• commutator-end housing commutator segments
  compound motor (compound-wound) compression
  spring counter- electromotive force (CEMF)
  cranking circuitdrive coil drive-end (DE)
  housing electromagnetic switch
• field coils field poles

Continued
4
KEY TERMS

• gear-reduction starters ground brushes
  growler testerholding coil hold-in winding
  hot brusheslap winding
• main field housing mesh spring mica movable
  pole shoe
• neutral safety switch overrunning clutch
• permanent-magnet field plunger lever pole
  shoes positive-engagement starter pull-in
  winding

Continued
5
KEY TERMS

• remote vehicle start (RVS)series motor shift
  fork lever shunt motor solenoid-operated
  starter starter drive through bolts
• undercut
• voltage-drop testing
• wave winding

6

• For any engine to start, it must first be
  rotated.It is the purpose and function of the
  cranking circuit to create the necessary power by
  converting electrical energy from the battery
  into mechanical energy at the starter motor and
  rotate the engine.

7
CRANKING CIRCUIT

• The cranking circuit includes mechanical and
  electrical parts required to crank the engine for
  starting. Early 1900s cranking force was the
  drivers arm. Modern cranking circuits include

1. The Starter motor. The starter is normally a 0.5-
   to 2.6-horsepower (0.4 to 2.0 kilowatts) electric
   motor that develops nearly 8 horsepower(6
   kilowatts) for a veryshort time when
   firstcranking a cold engine.

Figure 401A typical solenoid-operated starter.
Continued
8

1. The Battery. The battery must be of the correct
   capacity and be at least 75 charged to provide
   the necessary current and voltage for correct
   operation of the starter.
2. The Starter solenoid or relay. The high current
   required by the starter must be able to be turned
   on and off. A large switch would be required if
   the current were controlled by the driver
   directly. Instead, a small current switch
   (ignition switch) operates a solenoid or relay
   that controls the high starter current.
3. The Starter drive. The starter drive uses a small
   gear that contacts the engine flywheel gear and
   transmits starter motor power to rotate the
   engine.

Continued
9
Figure 402 Some column-mounted ignition
switches act directly on the contact points,
whereas others use a link from lock cylinder to
ignition switch.

1. The Ignition switch The ignition switch and
   safety control switches control the starter motor
   operation.

Figure 403 A typical wiring diagram of a
starter circuit.
The engine is cranked by an electric motor
controlled by akey-operated ignition switch.
Continued
10

• The ignition switch will not operate the starter
  unless the transmission is in neutral or park.
  Many manufacturers a neutral safety switch that
  opens the circuit between ignition switch and
  starter to prevent operation unless the gear
  selector is in neutral or park.Neutral safety
  switches can be adjusted by loosening the
  hold-down screws and moving the switch slightly
  to be certain the engine will crank only with the
  transmission in the neutral and park
  positions.Many manufacturers use a mechanical
  blocking device in the steering column to prevent
  the driver from turning the key switch to start
  unless the gear selector is in neutral or park.
  Many manual transmission vehicles also use a
  safety switch to permit cranking only if the
  clutch is depressed.

Continued
11
Whenever diagnosing any starter-related
problem, open the door of the vehicle and observe
the brightness of the dome or interior light(s)
while attempting to crank the engine. Why?
Watch the Dome Light

• The brightness of any electrical lamp is
  proportional to the voltage.
• Normal operation of the starter results in a
  slight dimming of the dome light.
• If the light remains bright, the problem is
  usually an open circuit in the control circuit.
• If the light goes out or almost goes out, the
  problem is usually a discharged or defective
  battery or a shorted or grounded armature of
  field coils inside the starter.

12
COMPUTER-CONTROLLED STARTING

• Some key-operated and most push-button-to-start
  ignition systems use the computer to crank the
  engine. The ignition switch start position on the
  push-to-start button is used as an input signal
  to the power train control module (PCM).The
  ignition key can be turned to the start position,
  released, and the PCM cranks the engine until it
  senses that the engine has started. The PCM can
  detect that the engine has started by looking at
  the engine speed signal.Normal cranking speed
  can vary between 100 and 250 rpm. If it exceeds
  400 rpm, the PCM determines the engine started
  and opens the circuit to the S (start) terminal
  of the starter solenoid.

Continued
13
Some customers have complained that the engine
cranks after they release the ignition key and
assume that there is a fault with the ignition
switch or starter circuit. If the vehicle is
equipped with computer-controlled starting, it is
normal for the engine to crank until it starts
and it may crank longer than the customer thinks
it should especially in cold weather.
Check That Extended Cranking May BeNormal
Operation
Computer-controlled starting is almost always
part of the system if a push-button start is used.
Before the PCM cranks the engine, the following
conditions must be met

• The brake pedal is depressed.
• The gear selector is in Park or Neutral.
• The correct key fob (code) is present in the
  vehicle.

Continued
14
Figure 404 The top button on this key fob is
the remote start button.

• Remote vehicle start (RVS) is a system that
  allows the driver to start the engine of the
  vehicle from inside the house or building from a
  distance of about 200 feet (65 meters).

The doors remain locked so the possibility of
theft is reduced.
This feature allows the heater or
air-conditioning system to start before the
driver arrives.
NOTE Most remote start systems will turn off
the engine after 10 minutes of run time unless
reset by the use of the remote.
15
HOW THE STARTER MOTOR WORKS

• A starter consists of a main field housing, one
  end of which is called a commutator-end (or
  brush-end) housing and the other end a drive-end
  housing.The drive-end housing contains the
  drive pinion gear, which meshes with the engine
  flywheel gear teeth to start the engine.The
  commutator-end plate supports the end containing
  the starter brushes. Through bolts hold the three
  components together.See Figure 405.

Continued
16
Figure 405 A typical starter motor.
Continued
17

• A starter uses electromagnetic principles to
  convert electrical energy (up to 500 amps) to
  mechanical power up to 8 hp (6 kw) to crank the
  engine.The steel housing of the starter motor
  contains four electromagnets that are connected
  directly to the positive post of the battery to
  provide a strong magnetic field inside the
  starter. Current for the starter is controlled by
  a solenoid or relay controlled by the
  driver-operated ignition switch.The
  electromagnets use heavy copper or aluminum wire
  wrapped around a soft-iron core. The core is
  contoured to fit against the rounded internal
  surface of the starter frame. The soft-iron cores
  are called pole shoes.

Continued
18

• Two of the four pole shoes are wrapped with
  copper wire in one direction to create a north
  pole magnet, the others wrapped to create a south
  pole.When energized, these magnets create
  strong magnetic fields inside the starter
  housing. They are called field coils. The
  soft-iron cores (pole shoes) are called field
  poles.
• Inside the field coils is an armature supported
  with bushings at both ends, which permit it to
  rotate. It is constructed of thin, circular disks
  of steel laminated together and wound lengthwise
  with heavy-gauge insulated copper wire.The
  laminated iron core supports the copper loops of
  wire and helps concentrate the magnetic field
  produced by the coils.

Continued
19

• The ends of the copper armature windings are
  soldered to the commutator segments. Current
  passing through the field coils is connected to
  the commutator of the armature by brushes that
  can move over the segments of the rotating
  armature. They are made of copper and carbon.
  Copper is a good conductor, and carbon added to
  starter brushes helps provide graphite-type
  lubrication needed to reduce wear of brushes and
  commutator segments.The starter uses four
  brushestwo to transfer current from field coils
  to armature, and two for the ground return path
  for current flow through the armature. See Figure
  406.Two hot brushes are in holders, insulated
  from the housing. Two ground brushes primarily
  use bare, stranded copper wire connections to the
  brushes. The ground brush holders are not
  insulated and attach directly to the field
  housing.

Continued
20
Figure 406 This series-wound electric motor
shows the basic operation with only two brushes
one hot brush and one ground brush. The current
flows through both field coils, then through the
hot brush and through the loop winding of the
armature before reaching ground through the
ground brush.

• Current travels throughbrushes into
  armaturewindings, where othermagnetic fields
  arecreated around eachcopper wire loop inthe
  armature.

The two magneticfields created insidethe
starter housingcreate force thatrotates the
armature.
21
HOW MAGNETIC FIELDS TURN AN ARMATURE

• A magnetic field surrounds every conductor
  carrying a current. Field strength is increased
  as current flow (in amps) is increased.Inside
  the starter housing is a strong magnetic field
  created by the field coil magnets. The armature,
  a conductor, is inside this strong field, with
  little clearance between armature and field
  coils.The two magnetic fields act together, and
  their lines of force bunch up or are strong on
  one side of the armature loop wire and become
  weak on the other side of the conductor.This
  causes the conductor (armature) to move from the
  area of strong magnetic field strength toward the
  area of weak magnetic field strength. This causes
  the armature to rotate.

Continued
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Figure 407 The interaction of the magnetic
fields of the armature loops and field coils
creates a stronger magnetic field on the right
side of the conductor, causing the armature loop
to move toward the left.
Continued
23
Figure 408 The armature loops rotate due to the
difference in the strength of the magnetic field.
The loops move from a strong magnetic field
strength toward a weaker magnetic field strength.

• This rotation force (torque) is increased as the
  current flowing through the starter motor
  increases. The torque of a starter is determined
  by the strength of the magnetic fields inside the
  starter. Magnetic field strength is measured in
  ampere-turns.

Continued
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Figure 409 Pole shoes and field windings
installed in the housing.

• If the current or number of turns of wire are
  increased, magnetic field strength is increased.

The magnetic field of the starter motor is
provided by two or more pole shoes and field
windings.
The pole shoes are made of iron and are attached
to the frame with large screws.
Continued
25
Figure 4010 Magnetic lines of force in a
four-pole motor.

• This shows paths ofmagnetic flux lineswithin a
  four-polemotor.
• The field windingsare usually made ofheavy
  copper ribbonto increase current-carrying
  capacityand electromagneticfield strength.

Continued
26
Figure 4011 A pole shoe and field winding.

• Starter motors usually have four pole shoes and
  two to four field windings to provide a strong
  magnetic field within the motor.

Pole shoes that do not have field windings are
magnetized by flux lines from the wound poles.
27
TYPES OF STARTER MOTORS

• Starter motors provide high power at low starter
  motor speeds to crank an automotive engine at all
  temperatures and at cranking speed required for
  the engine to start (60 to 250 engine rpm).

Electric motors are classified according to the
internal electrical motor connections. Many
starter motors are series wound, which means the
current flows first through the field coils, then
in series through the armature, and finally
through the ground brushes.
Figure 4012 This wiring diagram illustrates the
construction of a series-wound electric motor.
All current flows through the field coils, then
the armature (in series) before reaching ground.
Continued
28

• Series Motors A series motor develops maximum
  torque at initial start (0 rpm) and less torque
  as speed increases. Commonly used for an
  automotive starter motor because of high starting
  power characteristics.Less torque develops at
  high RPM because a current produced in the
  starter itself acts against current from the
  battery. Called counter electromotive force or
  CEMF, this current works against battery voltage
  and is produced by electromagnetic induction in
  the armature conductors. This induced voltage
  operates against applied voltage supplied by the
  battery, reduces strength of the magnetic field
  in the starter and current draw of the
  starter.It is characteristic of series-wound
  motors to keep increasing in speed under light
  loads, which could lead to destruction of the
  starter motor unless controlled or prevented.

Continued
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Figure 4013 This wiring diagram illustrates
construction of a shunt-type electric motor.
Shunt type electric motors have the field coils
in parallel (or shunt) across the armature as
shown.

• Shunt Motors Shunt-type electric motors have
  field coils in parallel (or shunt) across the
  armature as shown here. A shunt motor does not
  decrease in torque at higher motor rpm, because
  the CEMF produced not decrease the field coil
  strength.

A shunt motor, however, does not produce as high
a starting torque as that of a series-wound
motor, and is not used for starters.
Small electric motors used in blower motors,
windshield wipers, power windows, and power seats
use permanent magnets.
To compensate for the lack of torque, all PM
starters use gear reduction to multiply starter
motor torque.
Continued
30
Figure 4014A compound motor is a combination of
series and shunt types, using part of the field
coils connected electrically in series with the
armature and some in parallel (shunt).

• Compound Motors A compound-wound, or compound,
  motor has operating characteristics of a series
  motor and a shunt-type motor, because some of the
  field coils are connected to the armature in
  series and some (usually only one) are connected
  directly to the battery in parallel (shunt) with
  the armature.

Compound-wound starter motors are commonly used
in Ford, GM and Chrysler starters. The
shunt-wound field coil is called a shunt coil and
is used to limit maximum speed of the starter.
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ARMATURE AND COMMUTATOR ASSEMBLY

• The motor armature shown has a laminated core.
  Insulation between laminations helps reduce eddy
  currents. For reduced resistance, armature
  conductors are made of a thick copper wire.

Figure 4015 A typical starter motor armature.
Continued
32
Figure 4016 An armature lap winding.

• Armatures are connected to the commutator in one
  of two ways. In a lap winding, the two ends of
  each conductor are attached to two adjacent
  commutator bars.

In a wave winding, the two ends are attached to
commutator bars 180 degrees apart (on opposite
sides of the commutator).
A lap-wound armature is more commonly used
because it offers less resistance.
The commutator is made of copper bars insulated
from each other by mica or some other insulating
material.
Continued
33
Figure 4017 The pinion gear meshes with the fly
wheel ring gear.

• Armature core, windings, and commutator are
  assembled on a long armature shaft.

This shaft also carries the pinion gear that
meshes with the engine flywheel ring gear.
The shaft is supported by bearings or bushings in
the end housings.
To supply the proper current to the armature, a
four-pole motor must have four brushes which are
held against the commutator by spring force.
Continued
34
Figure 4018 A cutaway of a typical starter
motor.
35
PERMANENT MAGNET FIELDS

• Permanent-magnet starter motors were developed by
  General Motors for automotive use in the
  mid-1980s. The permanent magnets used are an
  alloy of neodymium, iron, and boron.Almost 10
  times more powerful than permanent magnets used
  previously, permanent-magnet, planetary-drive
  starter motors are the first significant advance
  in starter design in decades. First introduced on
  Chrysler and GM models.Permanent magnets are
  used in place of the electromagnetic field coils
  and pole shoes, eliminating the motor field
  circuit, which eliminates wire-to-frame shorts,
  field coil welding, and other problems. The motor
  has only an armature circuit.

36
Figure 4019 This starter permanent-magnet field
housing was ruined when someone used a hammer on
the field housing in an attempt to fix a
starter that would not work. A total replacement
is the only solution in this case.

• Most of todays starters use permanent-magnet
  fields, and the magnets can be easily broken if
  hit. A magnet that is broken becomes two weaker
  magnets.

Some early PM starters used magnets that were
glued or bonded to the field housing.
If struck with a heavy tool, magnets could be
broken, with parts of the magnet falling onto the
armatureand into the bearing pockets, making the
starter impossible to repair or rebuild.
37
In the past, it was common to see service
technicians hitting a starter in their effort to
diagnose a no-crank condition. Often the shock of
the blow to the starter aligned or moved the
brushes, armature, and bushings. Many times, the
starter functioned after being hiteven if only
for a short time. However, most of todays
starters use permanent-magnet fields, and the
magnets can be easily broken if hit. A magnet
that is broken becomes two weaker magnets. Some
early PM starters used magnets that were glued or
bonded to the field housing. If struck with a
heavy tool, the magnets could be broken, with
parts of the magnet falling onto the armature and
into the bearing pockets, making the starter
impossible to repair or rebuild.
Dont Hit That Starter!
38
GEAR REDUCTION STARTERS

• Gear-reduction starters are used by many
  manufacturers. The purpose of reduction
  (typically 21 to 41) is to increase speed of
  the armature of the starter and provide the
  torque multiplication necessary to crank an
  engine. See Figure 4020.A starter motors
  maximum torque occurs at zero rpm and torque
  decreases with increasing rpm. A smaller starter
  using a gear-reduction design can produce the
  necessary cranking power with reduced starter
  amperage requirements.Lower current
  requirements mean smaller battery cables can be
  used. Permanent-magnet starters use a planetary
  gear set (a type of gear reduction) to provide
  the necessary torque for starting.

Continued
39
Figure 4020 Many gear-reduction starters use a
planetary gear-reduction assembly similar to that
used in an automatic transmission.
40
STARTER DRIVES

• A starter drive includes a small pinion gear that
  meshes with and rotates the larger gear on the
  flywheel for starting.

Figure 4021 A cutaway of a typical starter drive.
The ends of the starter pinion gear are tapered
to help the teeth mesh more easily without
damaging the flywheel ring gear teeth.
Continued
41

• The pinion gear must engage with the engine gear
  slightly before the starter motor rotates, to
  prevent serious damage to either the starter gear
  or the engine, but the pinion gear must be
  disengaged after the engine starts.The ratio of
  teeth on the engine gear to the number on the
  starter pinion is between 151 and 201. A
  typical small starter pinion gear has 9 teeth
  that turn an engine gear with 166 teeth. This
  provides an 181 gear reduction thus, the
  starter motor is rotating approximately 18 times
  faster than the engine.

Continued
42
Figure 4022 The ring gear to pinion gear ratio
is usually 151 to 201

• Normal cranking speed for the engine is 200 rpm.
  This means that the starter motor speed is 18
  times faster, or 3600 starter rpm (200 18
  3600).

If the engine started and accelerated to 2000 rpm
(normal cold engine speed), the starter would be
destroyed by the highspeed (36,000 rpm) ifnot
disengaged from the engine.
43

• Older-model starters often used a Bendix drive
  mechanism, which used inertia to engage the
  starter pinion with the engine flywheel gear.
  Inertia is the tendency of a stationary object to
  remain stationary, because of its weight, unless
  forced to move.On these older-model starters,
  the small starter pinion gear was attached to a
  shaft with threads, and the weight of this gear
  caused it to be spun along the threaded shaft and
  mesh with the flywheel whenever the starter motor
  spun.If the engine speed was greater than the
  starter speed, the pinion gear was forced back
  along the threaded shaft and out of mesh with the
  flywheel gear.

Continued
44

• All starter drive mechanisms use a type of
  one-way clutch that allows the starter to rotate
  the engine, but turns freely if engine speed is
  greater than starter motor speed.This clutch is
  called an overrunning clutch and protects the
  starter motor from damage if the ignition switch
  is held in the start position after engine
  start.The overrunning clutch, which is built in
  as a part of the starter drive unit, uses steel
  balls or rollers installed in tapered
  notches.Whenever the engine rotates faster than
  the starter pinion, the balls or rollers are
  forced out of the narrow tapered notch, allowing
  the pinion gear to turn freely (overruns).
• See Figure 4023.

Continued
45
Figure 4023 Operation of the overrunning
clutch. (a) Starter motor is driving the starter
pinion and cranking the engine. The rollers are
wedged against spring force into their slots. (b)
The engine has started and is rotating faster
than the starter armature. Spring force pushes
the rollers so they can rotate freely.
(a)
(b)

• This taper forces the balls or rollers tightly
  into the notch, when rotating in the direction
  necessary, to start the engine.

Continued
46
Figure 4024Cutaway of a solenoid-activated
starter showing the solenoid, shift lever, and
starter drive assembly that includes the starter
pinion and overrunning clutch with a mesh spring
in one unit.

• The spring between the drive tang or pulley and
  overrunning clutch and pinion is called a mesh
  spring and it helps cushion and control
  engagement of the starter drive pinion with the
  flywheel gear.

This spring is called a compression spring
because the starter solenoid or starter yoke
compresses the spring and the spring tension
causes the starter pinion to engage the engine
flywheel.
Continued
47
STARTER DRIVE OPERATION

• The starter drive (pinion gear) must be moved
  into mesh with the engine ring gear before the
  starter motor starts to spin. Most starters use a
  solenoid or magnetic pull of the shunt coil in
  the starter to engage the starter pinion.A
  starter drive is generally dependable and does
  not require replacement unless defective or worn.
  Major wear occurs in the overrunning clutch
  section of the starter drive unit.The steel
  balls or rollers wear and often do not wedge
  tightly into the tapered notches as is necessary
  for engine cranking.

Continued
48

• A worn starter drive can cause the starter motor
  to operate freely, not rotate the engine, and
  makes whining noise. The whine indicates the
  starter motor is operating and the starter drive
  is not rotating the engine flywheel.The entire
  starter drive is replaced as a unit. The
  overrunning clutch section of the starter drive
  cannot be serviced or repaired separately because
  the drive is a sealed unit.Starter drives are
  most likely to fail intermittently at first, then
  more frequently, until replacement becomes
  necessary. Intermittent starter drive failure
  (starter whine) is often most noticeable during
  cold weather.

49
Figure 4025A Ford movable-pole-shoe starter.
POSITIVE ENGAGEMENT STARTERS

• Positive-engagement starters, used on some old
  Ford engines, utilize the shunt coil winding of
  the starter to engage the starter drive.

High starting current is controlled by an
ignition switchoperated starter solenoid,
usually mountednear the positive battery post.
Continued
50

• When this control circuit is closed, current
  flows through a hollow coil (called a drive coil)
  that attracts a movable pole shoe. The movable
  metal pole shoe is attached to and engages the
  starter drive with a lever (called the plunger
  lever).When the starter drive has engaged the
  engine flywheel, a tang on the movable pole shoe
  opens a set of contact points. The contact
  points provide the ground return path for the
  drive coil operation.The movable pole shoe is
  held down (which keeps the starter drive engaged)
  by a smaller coil on the inside of the main drive
  coil. This coil is called the holding coil and
  it is strong enough to hold the starter drive
  engaged while permitting the flow of the maximum
  possible current to operate the starter.

Continued
51

• If the grounding contact points are severely
  pitted, the starter may not operate the starter
  drive or the starter motor because of the
  resulting poor ground for the drive coil. If
  the contact points are bent or damaged enough to
  prevent them from opening, the starter will
  clunk the starter drive into engagement but
  will not allow the starter motor to operate.

52
SOLENOID OPERATED STARTERS

• A starter solenoid is an electromagnetic switch
  containing two separate but connected
  electromagnetic windings. This switch is used to
  engage the starter drive and to control the
  current from the battery to the starter motor.

The two internal windings contain approximately
the same number of turns but are made from a
different gauge wire. Together both windings
produce a strong magnetic field that pulls a
metal plunger into the solenoid.The plunger is
attached to the starter drive through a shift
fork lever. When the ignition switch is turned to
the start position, the motion of the plunger
into the solenoid causes the starter drive to
move into mesh with the flywheel ring gear.
Continued
53
Figure 4026 Wiring diagram of a typical starter
solenoid. Notice that both the pull-in winding
and the hold-in winding are energized when the
ignition switch is first turned to the start
position. As soon as the solenoid contact disk
makes electrical contact with both B and M
terminals, the battery current is conducted to
the starter motor and electrically neutralizes
the pull-in winding.

• The heavier-gauge winding (called the pull-in
  winding) is needed to draw the plunger into the
  solenoid.

The lighter-gauge winding (called the hold-in
winding) produces enough magnetic force to keep
the plungerin position.
54

• The main purpose of using two separate windings
  is to permit as much current as possible to
  operate the starter and yet provide the magnetic
  field required to move the starter drive into
  engagement.The instant the plunger is drawn
  into the solenoid enough to engage the starter
  drive, the it makes contact with a metal disk
  that connects the battery terminal post of the
  solenoid to the motor terminal.This permits
  full battery current to flow through the solenoid
  to operate the starter motor. The contact disk
  also electrically bypasses the pull-in
  winding.The solenoid has to work to supply
  current to the starter. If the starter motor
  operates at all, the solenoid is working, even
  though it may have high external resistance that
  could cause slow starter motor operation.

55
STARTING SYSTEM TROUBLESHOOTING

• Proper operation of the starting system depends
  on a good battery, cables and connections, and
  good starter motor. Because a starting problem
  can be caused by a defective component anywhere
  in the starting circuit, it is important to check
  for the proper operation of each part of the
  circuit to diagnose and repair the problem
  quickly.

Continued
Continued
56
VOLTAGE DROP TESTING

• Voltage drop is the drop in voltage that occurs
  when current is flowing through a resistance. A
  voltage drop is the difference between voltage at
  the source and voltage at the electrical device
  to which it is flowing. The higher the voltage
  drop, the greater the resistance in the circuit.

NOTE Before a difference in voltage (voltage
drop) can be measured between the ends of a
battery cable, current must be flowing through
the cable. Resistance is not effective unless
current is flowing. If the engine is not being
cranked, current is not flowing through the
battery cables and the voltage drop cannot be
measured.
Continued
57
Many techs have asked, Why measure voltage
drop when resistance can be easily measured using
an ohmmeter? Think of a battery cable with all
strands of the cable broken, except for one
strand.
Voltage Drop is Resistance - Part 1

• If an ohmmeter were used to measure the
  resistance of the cable, the reading would be
  very low, probably less than 1 ohm. However, the
  cable is not capable of conducting the amount of
  current necessary to crank the engine.

In less severe cases, several strands can be
broken and can affect the operation of the
starter motor. While the resistance of the
battery cable will not indicate any increased
resistance, the restriction to current flow will
cause heat and a decrease in the voltage
available at the starter.
Since resistance is not effective until current
flows, measuring the voltage drop (differences in
voltage between two points) is the most accurate
method of determining the true resistance in a
circuit. How much is too much?
58
According to Bosch Corporation, all electrical
circuits should have a maximum of 3 loss of the
voltage of the circuit to resistance. Therefore,
in a 12-volt circuit, the maximum loss of voltage
in cables and connections should be 0.36 volt (12
X 0.03 0.36 volt.) The remaining 97 of the
circuit voltage (11.64 volts) is available to
operate the electrical device (load). Just
remember
Voltage Drop is Resistance - Part 2

• Low-voltage drop Low resistance
• High-voltage drop High resistance

59

• Even though voltage-drop testing can be performed
  on any electrical circuit, the most common areas
  of testing include the cranking circuit and the
  charging circuit wiring and connections.

High-voltage drop (high resistance) in the
cranking circuit wiring can cause slow engine
cranking with less than normal starter amperage
drain as a result of excessive circuit
resistance.If voltage drop is high enough, such
as could be caused by dirty battery terminals,
the starter may not operate. A typical symptom of
high resistance in the cranking circuit is a
clicking of the starter solenoid.Voltage-drop
testing of the wire involves connecting any
voltmeter (on the low scale) to the suspected
high-resistance cable ends and cranking the
engine. See Figures 4027 through 4029.
Continued
60
Figure 4027 Voltmeter hookups for voltage-drop
testing of a GM-type cranking circuit.
Continued
61
Figure 4028 Voltmeter hookups for voltage-drop
testing of a Ford-type cranking circuit.
Continued
62
Figure 4029 To test the voltage drop of the
battery cable connection, place one voltmeter
lead on the battery terminal and the other
voltmeter lead on the cable end and crank the
engine. The voltmeter will read the difference in
voltage between the two leads which should not
exceed 0.2 volt (200 mV).
NOTE Before a difference in voltage (voltage
drop) can be measured between the ends of a
battery cable, current must be flowing through
the cable. Resistance is not effective unless
current is flowing. If the engine is not being
cranked, current is not flowing through the
battery cables and the voltage drop cannot be
measured.
63
Voltage Drop Test

• Crank the engine with a voltmeter connected to
  the battery and record the reading, then again
  with the voltmeter connected across the starter
  and record the reading. If the difference in the
  two readings exceeds 0.5 volt, perform the
  following to determine the exact location of the
  voltage drop.Step 1 Connect the positive
  voltmeter test lead to the most-positive end of
  the cable being tested. The most-positive end of
  a cable is the end closest to the positive
  terminal of the battery.Step 2 Connect the
  negative voltmeter test lead to the other end of
  the cable being tested. With no current flowing
  through the cable, the voltmeter should read zero
  because both ends of the cable have the same
  voltage.

Continued
64

• Step 3 Crank the engine voltmeter should read
  less than 0.2 volt.Step 4 Evaluate results.
  If the voltmeter reads zero, the cable being
  tested has no resistance and is good. If the
  voltmeter reads higher than 0.2 volt, the cable
  has excessive resistance and should be replaced.
  Before replacing the cable, make certain
  connections at both ends of the cable being
  tested are clean and tight.

If a cable or connection is hot to the touch,
there is electrical resistance in the cable or
connection. The resistance changes electrical
energy into heat energy. Therefore, if a
voltmeter is not available, carefully touch the
battery cables and connections while cranking the
engine. If any cable or connection is hot to the
touch, it should be cleaned or replaced.
Heat Equals Resistance
Continued
65
When there is excessive current flow through
the cable, battery cables can overheat. The
amount of current (in amperes) is determined by
the power required to operate the starter motor.
A typical problem involved a vehicle driven to
Florida from Michigan.
Battery Cable Heat and Counter EMF

• The battery cables overheated when the driver
  tried to start the vehicle. At a service center,
  some technicians believed that the cause of the
  overheated cables was an oversized battery, which
  is often used in vehicles from northern climates.

Although it is true that a smaller battery can be
used in warmer climates, a large battery does
absolutely no harm and, in fact, generally lasts
longer than a smaller battery. The cause of the
problem was discovered (by testing) to be a
defective starter motor that rotated too slowly.
The too-slow rotation of the starter meant that
the starter was not producing the normal amount
of counter EMF or CEMF. The overall result was a
tremendous increase in current being drawn from
the battery, and it was this extra current flow
that heated the battery cables.
66
CONTROL CIRCUIT TESTING

• The control circuit for starting includes the
  battery, ignition switch, neutral or clutch
  safety switch, and starter solenoid.Whenever
  the ignition switch is rotated to the start
  position, current flows through the ignition
  switch and the neutral safety switch and
  activates the solenoid.

An open or break anywhere in the control circuit
will prevent operation of the starter motor.
Continued
67
Figure 4030 GM solenoid ohmmeter check. The
reading between 1 and 3 (S terminal and ground)
should be 0.4 to 0.6 ohm (hold-in winding). The
reading between 1 and 2 (S terminal and M
terminal) should be 0.2 to 0.4 ohm (pull-in
winding).
If a starter is inoperative, check for voltage at
the S (start) terminal of the starter solenoid.
Some newer models with antitheft controls use a
relay to open this control circuit to prevent
starter operation.
See Figure 4031 for a startersystem diagnostic
chart.
Continued
68
Figure 4031 Starter trouble diagnostic chart.
See the chart on Page 429 of your textbook.
69
SPECIFICATIONS FOR A STARTERAMPERAGE TEST

• Before performing a starter amperage test,be
  certain the batteryis sufficiently charged (75
  or more) and capable of supplying adequate
  startingcurrent.

Figure 4032 Starter current can be measured by
using a high-current clamp and a digital
multimeter or a specialized starting and charging
tester.
Continued
70
A starter amperage test should be performed
whenever the starter fails to operate normally
(is slow in cranking) or as part of a routine
electrical system inspection. If exact specs are
not available, the following can be used for
testing a starter on the vehicle

• Four-cylinder engines 150 to 185 amperes MAX
• Six-cylinder engines 160 to 200 amperes MAX
• Eight-cylinder engines 185 to 250 amperes MAX

Excessive current draw may indicate one or more
of the following

1. Binding of starter armature as a result of worn
   bushings
2. Oil too thick (viscosity too high) for weather
   conditions
3. Shorted or grounded starter windings or cables
4. Tight or seized engine
5. High resistance in the starter motor

Continued
71

The Starter That Croaked and the Jumping Battery
Cables - Part 1

• Once upon a time a vehicle would not start
  (crank). A technician at first hoped that the
  problem was a simple case of loose or corroded
  battery terminal connections but after the
  technician cleaned the cables, the starter still
  made no noise when the ignition switch was turned
  to the start position. The technician opened the
  vehicle door and observed the dome (interior)
  light. The light was bright, indicating that the
  battery voltage was relatively high and that the
  battery should be adequately charged to crank the
  engine. However, when the technician turned the
  ignition switch to the start position, the dome
  light went out completely! This indicated that
  the battery voltage went down considerably.

NOTE It is normal for the dome light to dim
during cranking as a result of the lowered
battery voltage during cranking. However, the
voltage should not drop below 9.6 volts, which
normally will still provide adequate voltage to
light the dome light dimly.
72

The Starter That Croaked and the Jumping Battery
Cables - Part 2

• The technician then arranged the two battery
  cables so that they were parallel for a short
  distance and repeated the test. As soon as the
  ignition switch was turned to the start position,
  the battery cables jumped toward each other. The
  technician knew that the engine was seized or the
  starter had a shorted or grounded field coil or
  armature.

This provided a direct path to ground for the
starter current, which resulted in a
substantially greater amount of current (in
amperes) leaving the battery than would normally
occur with a good starter. This amount of current
drain lowered the battery voltage so much that
the dome light did not light. Why did the battery
cables jump? The battery cables jumped because
the high current flow created a strong magnetic
field around each cable. Because one cable is
positive and the other cable is negative, the
magnetic fields were of opposite polarity and
were attracted toward each other.
73
STARTER REMOVAL

• Most manufacturers recommend the following
  general steps

Step 1 Disconnect the negative battery
cable.Step 2 Hoist the vehicle safely. Step
3 Remove the starter retaining bolts and lower
the starter to gain access to the wire(s)
connection(s) on the starter.Step 4
Disconnect the wire(s) from the starterremove
the starter.Step 5 Inspect the flywheel (flex
plate) for ring gear damage. Check that mounting
holes and flange are clean and smooth.
See the procedure in Figures 40-33 through 40-38
Continued
74
Figure 4033 Before disassembly of any starter,
mark the location of the through bolts on the
field housing. This makes reassembly easier.
Continued
75
Figure 4034 Removing the solenoid from the
starter on a GM-type starter assembly.
Continued
76
Figure 4035 Rotate the solenoid to remove it
from the starter housing. ( Caution The plunger
return spring exerts a force on the solenoid and
may cause injury if not carefully released.
Continued
77
Figure 4036 The brushes should be replaced if
worn to less than 50 of their original length.
Replace if less than 1/2-inch long (13
millimeters).
Continued
78
Figure 4037 An exploded view of a General
Motors starter.
Continued
79
Figure 4038 To replace the starter drive unit,
the retainer and clip must be removed from the
armature shaft. A box-end wrench and a hammer can
pop the retainer off of the spring clip.
80
STARTER DISASSEMBLY

• Starters are replaced as an assembly and are not
  disassembled. If the starter is to be inspected
  or repaired, disassemble the starter using the
  following steps

Step 1 Remove the solenoid from the starter
assembly if equipped.Step 2 Remove the
through bolts and separate the drive-end (DE)
housing from the field frame.Step 3 Remove
the armature assembly.
Continued
81
Figure 4039 Measuring an armature shaft for
runout usinga dial indicator and V- blocks.

• Testing Starter Armatures After the starter
  drive has been removed from the armature, it can
  be checked for run out using a dial indicator and
  V-blocks as shown.

Because loops of copper wire are interconnected
in the armature of a starter, an armature can be
accurately tested only by a growler.
A growler is a 110-volt AC test unit that
generates an alternating (60 hertz) magnetic
field around an armature.
When it is switched on, the moving magnetic field
creates an alternating current in the windings of
the armature.
Continued
82

• Armature Service If the armature tests OK, the
  commutator should be measured and machined on a
  lathe, if necessary, to be certain that the
  surface is smooth and round.Some manufacturers
  recommend that the insulation between the
  segments of the armature (mica or hard plastic)
  be undercut, as shown in Figure 4040.Mica is
  harder than copper and will form raised bumps
  as the copper segments of the commutator wear.
  Undercutting the mica permits a longer service
  life for this type of starter armature.

Continued
83
Figure 4040 Replacement starter brushes should
be installed so the beveled edge matches the
rotation of the commutator.
Continued
84

• Testing Starter Motor Field Coils With the
  armature removed from the starter motor, the
  field coils should be tested for opens and
  grounds.A powered test light or an
  ohmmeter can be used. To test for a grounded
  field coil, touch one lead of the tester to a
  field brush (insulated or hot) and the other end
  to the starter field housing.The ohmmeter
  should indicate infinity (no continuity), and the
  test light should not light. If there is
  continuity, replace the field coil housing
  assembly.

NOTE Many starters use removable field coils,
and these coils must be rewound using the proper
equipment and insulating materials. Usually,
the cost involved in replacing defective field
coils exceeds the cost of a replacement starter.
Continued
85

• Starter Brush Inspection Starter brushes should
  be replaced if the brush length is less than
  one-half of its original length (less than 1/2
  inch 13 millimeters).On some models of
  starter motors, the field brushes are serviced
  with the field coil assembly and the ground
  brushes with the brush holder.Many starters use
  brushes that are held in with screws and are
  easily replaced, whereas other starters may
  require soldering to remove and replace the
  brushes.

Continued
86

• Bench Testing Every starter should be tested
  before installation in a vehicle.The usual
  method includes clamping the starter in a vise to
  prevent rotation during operation and connecting
  heavy-gauge jumper wires (minimum 4 gauge) to a
  battery known to be good and to the starter.
  The starter motor should rotate as fast as
  specifications indicate and not draw more than
  the free-spinning amperage permitted. A typical
  amperage specification for a starter being tested
  on a bench (not installed in a vehicle) usually
  ranges from 60 to 100 amperes.

Continued
87
STARTER INSTALLATION

• After verifying the starter assembly is
  functioning correctly, the following are the
  usual steps performed to install a starter.

Step 1 Check service information for the exact
wiring connections to the starter and/or
solenoid.Step 2 Verify that all electrical
connections on the starter motor and/or solenoid
are correct for the vehicle and that they are in
good condition.Step 3 Attach the power and
control wires.Step 4 Install the starter, and
torque all the fasteners to factory
specifications.
Continued
88
Figure 4041 A shim (or half shim) may be needed
to provide the proper clearance between the
flywheel teeth of the engine and the pinion teeth
of the starter.

• Starter Drive-to-Flywheel Clearance For proper
  operation of the starter and absence of abnormal
  starter noise, there must be a slight clearance
  between the starter pinionand the engine
  flywheel ring gear.

If clearance is too great, the starter will
produce a high-pitched whine during cranking.
If the clearance is too small, the starter will
produce a high-pitched whine after the engine
starts, just as the ignition key is released.
89
NOTE Be sure that the locking nuts for the
studs are tight. Often the retaining nut that
holds the wire to the stud will be properly
tightened, but if the stud itself is loose,
cranking problems can occur.
Many GM starters use shims (thin metal strips)
between the flywheel and the engine block
mounting pad to provide the proper clearance.
NOTE Some manufacturers use shims under starter
drive-end housings during production. Other
manufacturers grind the mounting pads at the
factory for proper starter pinion gear clearance.
If any GM starter is replaced, the starter pinion
must be checked and corrected as necessary
to prevent starter damage and excessive noise.
Continued
90

• To be sure the starter is shimmed correctly, use
  this procedureStep 1 Place the starter in
  position finger tighten mounting bolts.Step 2
  Use an 1/8 inch diameter drill bit (or gauge
  tool) and insert between the armature shaft and a
  tooth of the engine flywheel.Step 3 If the
  gauge tool cannot be inserted, use a full-length
  shim across both the holes, moving the starter
  away from the flywheel.Step 4 If the gauge
  tool is loose between the shaft and the tooth of
  the engine flywheel, remove a shim or
  shims.Step 5 If no shims have been used and
  the fit of the gauge tool is too loose, add a
  half shim to the outside pad only. This moves the
  starter closer to the teeth of the engine
  flywheel.

Continued
91
CAUTION Be sure to install all factory heat
shields to help ensure proper starter operation
under all weather and driving conditions.
NOTE The major cause of broken drive-end
housings on starters is too small a clearance. If
the clearance cannot be measured, it is better to
put a shim between the engine block and the
starter than to leave one out and risk breaking a
drive-end housing.
92
Before installing a new or rebuilt starter in a
vehicle, be sure that both the positive cable and
the negative cable are in good condition. The
reason is all electrical power must have a
complete path from the power source, through the
electrical loads, and back to the power source.
This rule is true for all circuits, whether
series, parallel, or series-parallel type
Ground Wire Current Flow - Part 1

• As the current flows through resistances and
  loads (such as bulbs and
• coils), its voltage decreases because of the
  resistance (electrical load) in the circuit.
  Amperes is the unit of electricity that actually
  does the work ina circuit. The greater the
  current flow, the more electrical power
  available.

Because current flow is actually a measure of the
number of electronsmaking the trip through a
circuit, this same number of electrons also must
return to the power source. The electrical
pressure (voltage) on the return (ground) wires
is low (almost zero), but the current in amperes
must stillflow back to the battery. The battery
ground cable must be just as large as the
positive cable because just as many amperes
return as leave the battery. Still not convinced?
93
Connect a starting-charging-testing unit to a
vehicle. Instead of connecting the ampere probe
around the positive cable, connect it around the
ground cable (all cables should be within the
ampere probe if more than one ground cable is
connected to the battery terminal). All ammeter
readings should be the same if taken on the
positive or negative cables of the battery.
Ground Wire Current Flow - Part 2
NOTE Most starting-charging-testing units use
an arrow on the ammeter probe to show polarity.
Reversing the direction in which the arrow points
is often necessary to read the correct polarity
(positive or negative) on the tester display.
94
Most General Motors starter motors use a pad
mount and attach to the engine with bolts through
the drive-end (nose) housing. Many times when a
starter is replaced on a GM vehicle, the starter
makes noise because of improper starter
pinion-to-engine flywheel ring gear clearance.
Instead of spending a lot of time shimming the
new starter, simply remove the drive-end housing
from the original starter and install it on the
replacement starter.Because the original
starter did not produce excessive gear engagement
noise, the replacement starter should also be
okay. Reuse any shims that were used with the
original starter. This method is better than
having to remove and reinstall the replacement
starter several times until the proper clearance
is determined.
Reuse Drive-End Housings to Be Sure
95
STARTING SYSTEMTROUBLESHOOTING GUIDE
See the chart on Page 432 of your textbook.
96

• PHOTO SEQUENCE Starter Overhaul

Continued
97
(cont.)

• PHOTO SEQUENCE Starter Overhaul

Continued
98
(cont.)

• PHOTO SEQUENCE Starter Overhaul

Continued
99
(cont.)

• PHOTO SEQUENCE Starter Overhaul

100
SUMMARY

1. All starter motors use the principle of magnetic
   interaction between the field coils attached to
   the housing and the magnetic field of the
   armature.
2. Proper operation of the starter motor depends on
   the battery being at least 75 charged and the
   battery cables being of the correct size (gauge)
   and having no more than 0.2-volt drop.
3. Voltage-drop testing includes cranking the
   engine, measuring the drop in voltage from the
   battery to the starter, and measuring the drop in
   voltage from the negative terminal of the battery
   to the engine block.

Continued
101
SUMMARY
(cont.)

1. The cranking circuit should be tested for proper
   amperage draw.
2. An open in the control circuit can prevent
   starter motor operation.

102
end