<ul><li>Describe how the cranking circuit works. </li></ul><ul><li>Explain how to disassemble and reassemble a starter motor and solenoid. </li></ul><ul><li>Discuss how to test the cranking circuit. </li></ul><ul><li>Describe how to perform cranking system testing procedures. </li></ul>OBJECTIVES: After studying Chapter 40, the reader should be able to:
<ul><li>ampere-turns • armature bench testing • brush-end housing • brushes </li></ul><ul><li>commutator-end housing • commutator segments • compound motor (compound-wound) • compression spring • counter- electromotive force (CEMF) • cranking circuit drive coil • drive-end (DE) housing • electromagnetic switch </li></ul><ul><li>field coils • field poles </li></ul>KEY TERMS: Continued
<ul><li>gear-reduction starters • ground brushes • growler tester holding coil • hold-in winding • hot brushes lap winding </li></ul><ul><li>main field housing • mesh spring • mica • movable pole shoe </li></ul><ul><li>neutral safety switch • overrunning clutch </li></ul><ul><li>permanent-magnet field • plunger lever • pole shoes • positive-engagement starter • pull-in winding </li></ul>KEY TERMS: Continued
<ul><li>remote vehicle start (RVS) series motor • shift fork lever • shunt motor • solenoid-operated starter • starter drive through bolts </li></ul><ul><li>undercut </li></ul><ul><li>voltage-drop testing </li></ul><ul><li>wave winding </li></ul>KEY TERMS:
<ul><li>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. </li></ul>
CRANKING CIRCUIT <ul><li>The cranking circuit includes mechanical and electrical parts required to crank the engine for starting. Early 1900s cranking force was the driver’s arm. Modern cranking circuits include: </li></ul>Continued <ul><li>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 very short time when first cranking a cold engine. </li></ul>Figure 40–1 A typical solenoid-operated starter.
<ul><li>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. </li></ul><ul><li>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. </li></ul><ul><li>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. </li></ul>Continued
Figure 40–2 Some column-mounted ignition switches act directly on the contact points, whereas others use a link from lock cylinder to ignition switch. <ul><li>The Ignition switch The ignition switch and safety control switches control the starter motor operation. </li></ul>Figure 40–3 A typical wiring diagram of a starter circuit. Continued The engine is cranked by an electric motor controlled by a key-operated ignition switch.
<ul><li>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. </li></ul>Continued
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 <ul><li>The brightness of any electrical lamp is proportional to the voltage. </li></ul><ul><li>Normal operation of the starter results in a slight dimming of the dome light. </li></ul><ul><li>If the light remains bright, the problem is usually an open circuit in the control circuit. </li></ul><ul><li>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. </li></ul>
COMPUTER-CONTROLLED STARTING <ul><li>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. </li></ul>Continued
<ul><li>The brake pedal is depressed. </li></ul><ul><li>The gear selector is in Park or Neutral. </li></ul><ul><li>The correct key fob (code) is present in the vehicle. </li></ul>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 Be Normal 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: Continued
Figure 40–4 The top button on this key fob is the remote start button. <ul><li>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). </li></ul>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.
HOW THE STARTER MOTOR WORKS <ul><li>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 40–5. </li></ul>Continued
Figure 40–5 A typical starter motor. Continued
<ul><li>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 . </li></ul>Continued
<ul><li>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 . </li></ul><ul><li>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. </li></ul>Continued
<ul><li>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 brushes—two to transfer current from field coils to armature, and two for the ground return path for current flow through the armature. See Figure 40–6. 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. </li></ul>Continued
Figure 40–6 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. <ul><li>Current travels through brushes into armature windings, where other magnetic fields are created around each copper wire loop in the armature. </li></ul>The two magnetic fields created inside the starter housing create force that rotates the armature.
HOW MAGNETIC FIELDS TURN AN ARMATURE <ul><li>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. </li></ul>Continued
Figure 40–7 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
Figure 40–8 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. <ul><li>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 . </li></ul>Continued
Figure 40–9 Pole shoes and field windings installed in the housing. <ul><li>If the current or number of turns of wire are increased, magnetic field strength is increased. </li></ul>The pole shoes are made of iron and are attached to the frame with large screws. The magnetic field of the starter motor is provided by two or more pole shoes and field windings. Continued
<ul><li>This shows paths of magnetic flux lines within a four-pole motor. </li></ul><ul><li>The field windings are usually made of heavy copper ribbon to increase current- carrying capacity and electromagnetic field strength. </li></ul>Figure 40–10 Magnetic lines of force in a four-pole motor. Continued
<ul><li>Starter motors usually have four pole shoes and two to four field windings to provide a strong magnetic field within the motor. </li></ul>Figure 40–11 A pole shoe and field winding. Pole shoes that do not have field windings are magnetized by flux lines from the wound poles.
TYPES OF STARTER MOTORS <ul><li>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). </li></ul>Continued Figure 40–12 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. 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.
<ul><li>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. </li></ul>Continued
<ul><li>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. </li></ul>Figure 40–13 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. Continued Small electric motors used in blower motors, windshield wipers, power windows, and power seats use permanent magnets. 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. To compensate for the lack of torque, all PM starters use gear reduction to multiply starter motor torque.
<ul><li>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. </li></ul>Figure 40–14 A 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-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.
ARMATURE AND COMMUTATOR ASSEMBLY <ul><li>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. </li></ul>Continued Figure 40–15 A typical starter motor armature.
<ul><li>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. </li></ul>Figure 40–16 An armature lap winding. 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
Figure 40–17 The pinion gear meshes with the fly wheel ring gear. <ul><li>Armature core, windings, and commutator are assembled on a long armature shaft. </li></ul>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
Figure 40–18 A cutaway of a typical starter motor.
PERMANENT MAGNET FIELDS <ul><li>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. </li></ul>
Figure 40–19 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. <ul><li>Most of today’s starters use permanent-magnet fields, and the magnets can be easily broken if hit. A magnet that is broken becomes two weaker magnets. </li></ul>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 armature and into the bearing pockets, making the starter impossible to repair or rebuild.
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 hit—even if only for a short time. However, most of today’s 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. Don’t Hit That Starter!
GEAR REDUCTION STARTERS <ul><li>Gear - reduction starters are used by many manufacturers. The purpose of reduction (typically 2:1 to 4:1) is to increase speed of the armature of the starter and provide the torque multiplication necessary to crank an engine. See Figure 40–20. A starter motor’s 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. </li></ul>Continued
Figure 40–20 Many gear-reduction starters use a planetary gear-reduction assembly similar to that used in an automatic transmission.
STARTER DRIVES <ul><li>A starter drive includes a small pinion gear that meshes with and rotates the larger gear on the flywheel for starting. </li></ul>Continued The ends of the starter pinion gear are tapered to help the teeth mesh more easily without damaging the flywheel ring gear teeth. Figure 40–21 A cutaway of a typical starter drive.
<ul><li>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 15:1 and 20:1. A typical small starter pinion gear has 9 teeth that turn an engine gear with 166 teeth. This provides an 18:1 gear reduction; thus, the starter motor is rotating approximately 18 times faster than the engine. </li></ul>Continued
Figure 40–22 The ring gear to pinion gear ratio is usually 15:1 to 20:1 <ul><li>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). </li></ul>If the engine started and accelerated to 2000 rpm (normal cold engine speed), the starter would be destroyed by the high speed (36,000 rpm) if not disengaged from the engine.
<ul><li>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. </li></ul>Continued
<ul><li>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). </li></ul><ul><li>See Figure 40–23. </li></ul>Continued
Figure 40–23 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. <ul><li>This taper forces the balls or rollers tightly into the notch, when rotating in the direction necessary, to start the engine. </li></ul>(a) (b) Continued
<ul><li>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. </li></ul>Figure 40–24 Cutaway 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. 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
STARTER DRIVE OPERATION <ul><li>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. </li></ul>Continued
<ul><li>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. </li></ul>
Figure 40–25 A Ford movable-pole-shoe starter. <ul><li>Positive - engagement starters , used on some old Ford engines, utilize the shunt coil winding of the starter to engage the starter drive. </li></ul>High starting current is controlled by an ignition switch–operated starter solenoid, usually mounted near the positive battery post. Continued POSITIVE ENGAGEMENT STARTERS
<ul><li>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. </li></ul>Continued
<ul><li>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. </li></ul>
SOLENOID OPERATED STARTERS <ul><li>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. </li></ul>Continued 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.
Figure 40–26 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. <ul><li>The heavier-gauge winding (called the pull-in winding ) is needed to draw the plunger into the solenoid. </li></ul>The lighter-gauge winding (called the hold-in winding ) produces enough magnetic force to keep the plunger in position.
<ul><li>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. </li></ul>
STARTING SYSTEM TROUBLESHOOTING <ul><li>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. </li></ul>Continued Continued
VOLTAGE DROP TESTING <ul><li>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. </li></ul>Continued 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 flowin g. If the engine is not being cranked, current is not flowing through the battery cables and the voltage drop cannot be measured.
<ul><li>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. </li></ul>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 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?
<ul><li>Low-voltage drop Low resistance </li></ul><ul><li>High-voltage drop High resistance </li></ul>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
<ul><li>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. </li></ul>Continued 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 40–27 through 40–29.
Figure 40–27 Voltmeter hookups for voltage-drop testing of a GM-type cranking circuit. Continued
Figure 40–28 Voltmeter hookups for voltage-drop testing of a Ford-type cranking circuit. Continued
Figure 40–29 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 flowin g. If the engine is not being cranked, current is not flowing through the battery cables and the voltage drop cannot be measured.
<ul><li>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. </li></ul>Continued Voltage Drop Test
<ul><li>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. </li></ul>Continued 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
<ul><li>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. </li></ul>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 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.
CONTROL CIRCUIT TESTING <ul><li>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. </li></ul>Continued An open or break anywhere in the control circuit will prevent operation of the starter motor.
Figure 40–30 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 40–31 for a starter system diagnostic chart. Continued
Figure 40–31 Starter trouble diagnostic chart. See the chart on Page 429 of your textbook.
<ul><li>Before performing a starter amperage test, be certain the battery is sufficiently charged (75% or more) and capable of supplying adequate starting current. </li></ul>SPECIFICATIONS FOR A STARTER AMPERAGE TEST Figure 40–32 Starter current can be measured by using a high-current clamp and a digital multimeter or a specialized starting and charging tester. Continued
Continued <ul><li>Four-cylinder engines: 150 to 185 amperes MAX </li></ul><ul><li>Six-cylinder engines: 160 to 200 amperes MAX </li></ul><ul><li>Eight-cylinder engines: 185 to 250 amperes MAX </li></ul><ul><li>Binding of starter armature as a result of worn bushings </li></ul><ul><li>Oil too thick (viscosity too high) for weather conditions </li></ul><ul><li>Shorted or grounded starter windings or cables </li></ul><ul><li>Tight or seized engine </li></ul><ul><li>High resistance in the starter motor </li></ul>Excessive current draw may indicate one or more of the following: 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:
<ul><li>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. </li></ul>The Starter That Croaked and the Jumping Battery Cables - Part 1 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.
<ul><li>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. </li></ul>The Starter That Croaked and the Jumping Battery Cables - Part 2 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.
STARTER REMOVAL <ul><li>Most manufacturers recommend the following general steps: </li></ul>Continued 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 starter;remove 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
Figure 40–33 Before disassembly of any starter, mark the location of the through bolts on the field housing. This makes reassembly easier. Continued
Figure 40–34 Removing the solenoid from the starter on a GM-type starter assembly. Continued
Figure 40–35 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
Figure 40–36 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
Figure 40–37 An exploded view of a General Motors starter. Continued
Figure 40–38 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.
STARTER DISASSEMBLY <ul><li>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: </li></ul>Continued 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.
<ul><li>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. </li></ul>Figure 40–39 Measuring an armature shaft for runout using a dial indicator and V- blocks. 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
<ul><li>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 40–40. 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. </li></ul>Continued
Figure 40–40 Replacement starter brushes should be installed so the beveled edge matches the rotation of the commutator. Continued
<ul><li>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. </li></ul>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
<ul><li>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. </li></ul>Continued
<ul><li>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. </li></ul>Continued
STARTER INSTALLATION <ul><li>After verifying the starter assembly is functioning correctly, the following are the usual steps performed to install a starter. </li></ul>Continued 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.
Figure 40–41 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. <ul><li>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 pinion and the engine flywheel ring gear. </li></ul>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.
Continued Many GM starters use shims (thin metal strips) between the flywheel and the engine block mounting pad to provide the proper clearance. 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. 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.
<ul><li>To be sure the starter is shimmed correctly, use this procedure: Step #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. </li></ul>Continued
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.
<ul><li>As the current flows through resistances and loads (such as bulbs and </li></ul><ul><li>coils), its voltage decreases because of the resistance (electrical load) in the circuit. Amperes is the unit of electricity that actually does the work in a circuit. The greater the current flow, the more electrical power available. </li></ul>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 Because current flow is actually a measure of the number of electrons making 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 still flow 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 ?
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.
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
STARTING SYSTEM TROUBLESHOOTING GUIDE See the chart on Page 432 of your textbook.
SUMMARY <ul><li>All starter motors use the principle of magnetic interaction between the field coils attached to the housing and the magnetic field of the armature. </li></ul><ul><li>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. </li></ul><ul><li>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. </li></ul>Continued
SUMMARY <ul><li>The cranking circuit should be tested for proper amperage draw. </li></ul><ul><li>An open in the control circuit can prevent starter motor operation. </li></ul>( cont. )