This month, I will continue with a complete overview of the ignition system from the Packard Service Training Program booklet, with my personal notes added. This is relevant for most old cars with points, plugs and condenser systems, and specific for 19th (1941), 20th (1942) and 21st (1946-47) Series Packards. Our '46 is an Autolite, 6 volt, positive ground. We are assuming a good battery, spark plugs and distributor.
CONSTRUCTION AND OPERATION: Good ignition, plus good carburetion, plus good compression equals good engine performance. Good engine performance can be obtained only when all three are functioning properly. Since good ignition is one of the requirements of good engine performance, the function, construction and operation of the ignition system must be clearly understood, so that an accurate diagnosis of ignition troubles can be made and the ignition system can be properly serviced. The function of the ignition system is to provide a spark of the correct intensity at the proper time to ignite the mixture of fuel and air in the cylinder.
DESCRIPTION: The ignition system of Packard cars consists of the following essential units:
A- A battery and generator as the source of power
B- An ignition switch to control the starting and stopping of the engine.
C- An ignition coil to step up the voltage D- A distributor to direct the spark to the proper spark plugs at the correct time.
E. Ignition cables to carry the current to the spark plugs.
F. Spark plugs to ignite the mixture.
Actually, the generator is the source of all electrical energy in the car. It supplies power for the ignition, lights, heater, radio and other accessories. The battery stores some of the generated energy in chemical form to be used when the generator is not operating. But, for the purpose of simplifying the ignition circuits, we will assume that the battery is the source of power for the ignition system. The function of the ignition switch is to close and open the circuit between the battery and the ignition circuit. The voltage of the generator and battery is limited and is not great enough to cause a spark to jump the spark plug gap. Therefore, the voltage must be increased. This is accomplished by the use of an ignition coil.
IGNITION COIL The function of an ignition coil is to transform the low voltage supplied by the battery into the high voltage necessary to jump the spark plug gap. In simple language, it is a transformer. The ignition coil is an electrical unit having two windings: a primary and a secondary winding. The secondary winding, which consists of many thousand turns of fine wire, is wound around a soft iron core. The primary winding, which consists of a few turns of heavier wire is wound over the secondary winding. A soft iron shell encloses both windings and provides an outer path for the magnetic field. Thin insulation is placed between the winding layers of the primary and secondary windings and between the outside of the primary winding and the coil outer shell. The coil is a sealed unit to protect the windings from moisture and air. When the ignition switch is closed, current flows through the primary winding. As long as the flow of current is steady in the primary winding, there is no flow of current in the secondary winding. But, if the flow of current is suddenly stopped in the primary winding, a high voltage will be induced in the secondary winding. The flow of current in the primary winding is stopped by the use of a set of breaker contacts which are connected in the primary circuit and are located in the distributor.
TESTING THE COIL: The symptoms of a bad coil are hard starting, chronic high speed missing, and cutting out during acceleration. To test the coil, first remove the high tension cable between the coil and the distributor at the distributor cap. Hold the end of the cable about 3/16" away from some grounded part of the engine and crank the starter with the ignition switch ON. A blue spark should jump the gap, indicating a good coil, or a weak yellowish or red spark indicates a bad coil. The test must be done with the battery, points and condenser in good condition. Another test using a 6-12 volt test light with two leads can be done: Remove the distributor cap, then crank the engine until the points open. Turn the ignition switch on, connect one test light lead to ground on the engine and the other lead to the coil's primary terminal that goes to the distributor (this is the + on our car). If the test light bulb lights, that shows the coil is getting current and the primary windings are right. If the bulb lights when the test lead is touched to the coil's other terminal (one not to the distributor) the coil is bad and the primary windings are faulty.
DISTRIBUTOR: The distributor has two functions:
1. To provide a ground for the primary circuit through the contact points and to interrupt the flow of primary current at the right time. 2. To distribute the secondary high voltage to the proper spark plug at the proper time.
The Packard distributor is of the singer breaker type using centrifugal governor advance and vacuum advance for automatic timing control. Four models of distributors are used on the 1946 21st Series Packard cars: The Auto-Lite IGC 4505 and the Delco-Remy 1110132 are used on the Six, the Auto-Lite IGP 4502A is used on the Eight, and the Auto-Lite IGT 4203 is used on the Super Eight. Ours is the Auto-Lite IGP 4502A. The distributor drive shaft is driven by a slotted coupling of the oil pump gear. The oil pump gear, which meshes with a gear on the camshaft, rotates the distributor shaft at camshaft speed which is one-half engine speed. The other end of the distributor shaft is connected through a governor mechanism to the distributor cam and rotor.
PRIMARY CIRCUIT: The distributor primary circuit contains a set of breaker contacts, one of which is on a stationary bracket but is adjustable, the other on a movable arm. The contacts are opened by the distributor cam acting against a molded insulated rubbing block attached to the movable arm. The contacts are closed by the action of a flat spring attached to the contact arm. The contacts are mounted on the distributor plate and are connected in the primary circuit.
When the breaker contacts are closed, current flows through the primary winding creating a magnetic field around the primary winding. As the cam is rotated, it opens the contacts, breaking the primary circuit. This collapses the magnetic field around the primary winding and induces a high voltage in the secondary winding. The collapse of the magnetic field also induces a voltage in the primary winding. The effect of this inductance is a tendency to keep current flowing in the same direction in the primary circuit. The voltage induced in the primary winding is great enough to cause an arc at the contact points. If it were not for the condenser, this arc would prevent the sudden collapse of the magnetic field and, consequently, a low secondary voltage.
CONDENSER: The condenser is provided to bring the flow of current in the primary winding to a quick controlled stop. The condenser prevents arcing at the contacts by absorbing and momentarily holding a charge of primary current. When the condenser discharges the current, it speeds the collapse of the magnetic field and helps to induce the high voltage in the secondary winding. The condenser is made up of two layers of metal foil, insulated by two layers of hallo wax impregnated paper. To save space, these layers of foil and wax paper are rolled into a small roll and enclosed in a small metal shield. The outer layer of foil is connected to the outer shell which is grounded to the distributor plate and the inner foil is connected to a lead wire which is connected to the contact arm terminal. The condenser shell is sealed by a gasket to protect it from moisture and air. The gasket is retained by the crimped edge of the shell.
CONDENSER TEST: Condensers help the coil by the reduction of arcing and giving longer point life. They are rated specifically for your car's ignition system in MFD (microfarads). Our '46 is .20-.25 MFD. A grounded primary circuit with misfiring at high speed can be the result of a bad condenser. Fortunately, condensers are inexpensive and easy to replace. But you may want to run a few tests before replacing it. A common problem is the condenser's mounting strap becomes loose. Before tightening it, lightly sanding the strap and condenser at strap contact with emery cloth can help to make a good ground. A loose condenser can cause an erratic ignition. When the points are burned or pitted, it's usually the condenser, or the points set too close. To test the condenser, you can buy a coil/condenser tester, or use a multimeter.
MULTIMETER TEST: First, remove the condenser (the metal case is the ground and the lead wire is the hot). Discharge the condenser by shorting the lead wire to the car. Switch the meter to Ohms. Set the resistance range to the highest setting. Connect the test leads together and zero the meter. Touch the red lead to the "hot" lead on the condenser and place the black lead to the metal case of the condenser. On an analog meter, the needle should jump slightly to the right toward 0 ohms, then drop back to the left towards infinity. By holding the test leads in place for 20 seconds will charge the condenser. If this test shows any other readings, the condenser is leaking and is bad.
In addition to closing and opening of the contacts, the purpose of the distributor is to deliver the high voltage to the proper spark plug at the proper time. The exact instant at which the spark must occur for most efficient engine operation is determined by the:
1. Speed of the engine
2. Throttle opening of the carburetor
3. Engine load. The exact ignition timing to satisfy these conditions is accomplished automatically by the centrifugal governor advance and vacuum advance mechanisms.
CENTRIFUGAL GOVERNOR ADVANCE: The centrifugal governor advance is so designed that, as engine speed increases, the centrifugal force of the rotating flyweights will gradually throw the weights outwardly and will automatically advance the distributor cam in relation to the distributor shaft. The rate and amount of advance is controlled by the design and calibration of the flyweight springs and the centrifugal governor flyweights.
VACUUM ADVANCE: During part throttle (or part load) operation, there is a great vacuum in the intake manifold. Consequently, the charge taken into the cylinder is not so highly compressed as it is when the engine is under heavy load. With this condition, an additional spark advance will increase fuel economy. This is accomplished by the use of the "part load" advance or vacuum advance, as it is commonly known. The vacuum advance mechanism consists of a spring-loaded diaphragm operating in a vacuum chamber and is connected through a linkage to a lever on the distributor. The chamber on the spring-loaded side of the diaphragm is air tight and is connected through a vacuum line to a small opening in the carburetor throttle body. This opening is located just above the throttle valve when the the throttle is in idle position. There is no vacuum at this opening during idle and, consequently, no vacuum advance. When the throttle is opened, it uncovers the opening of the vacuum passage, which is connected by a vacuum line to the distributor vacuum chamber. The vacuum acting on the diaphragm moves the diaphragm and compresses the spring in the chamber. The diaphragm, connected by a linkage, rotates the distributor in its mounting to advance the timing. On the Super Eight distributor, the vacuum advance mechanism rotates ONLY the breaker plate. Under heavy load or full throttle operation, when the manifold vacuum drops, the spring pressure on the diaphragm will rotate the distributor backward, retarding the timing to prevent detonation. The spring load is calibrated to give most efficient operation under any operating condition. It is adjustable by the use of shims in the spring seat.
SECONDARY CIRCUIT DISTRIBUTOR CAP: The distributor cap covers the distributor and is molded of a non-conductive material. It contains one center carbon contact, to which the secondary wire from the coil is connected, and a series of brass contacts, each of which is connected to a spark plug by a spark plug cable in the correct sequence of the firing order of the engine.
DISTRIBUTOR ROTOR: The rotor also is molded of a non-conductive material. It carries a steel segment that makes contact between the center contact of the distributor cap and the brass contacts. Actually, the segment does not touch the brass contacts, but it comes so near to them that the high tension current can jump an arc to the brass contacts. The rotor is rotated by the distributor cam and is so timed that the secondary current from the coil is distributed through the radial contacts and the spark plug cables to each spark plug at the proper time and at each opening of the breaker contact.
IGNITION CABLES: The ignition cables carry the current to the spark plugs. These cables contain several strands of low resistance wire and are covered by a rubberized insulating material. The insulating material is protected by a cotton braid and a lacquer coating. High tension conduit is used to support the cables and keep them from chafing. We always use stranded wires on vehicles with points and condenser ignition systems. These wires will help produce the 20,000 volts at the spark plugs these old cars require. Suppression wires won't do that.
SPARK PLUGS: The spark plugs are rated according to their temperature range. A plug with a long porcelain exposed to the combustion chamber is "hot" plug. A plug with a shorter porcelain is a "colder" plug. The spark plugs used in Packard cars are the AC-104, The Champion Y4A, and the Auto-Lite P-4. The thread size is 10mm. Each is of the proper heat range and should always be replaced with the same type plug.
The ignition system of Packard cars consists of the following essential units:
A- A battery and generator as the source of power
B- An ignition switch to control the starting and stopping of the engine.
C- An ignition coil to step up the voltage
D- A distributor to direct the spark to the proper spark plugs at the correct time.
E. Ignition cables to carry the current to the spark plugs.
F. Spark plugs to ignite the mixture.
SEQUENCE OF OPERATION:
With the ignition key turned on, closing the distributor contact points completes the ignition primary circuit. The current flows from the battery, through the ammeter, the ignition switch, the primary winding of the coil, and the contact points to ground. This flow of current through the primary winding creates a magnetic field around the coil and through the core. The current flow and magnetic field, however, do not increase to their peak instantly. It takes a small fraction of a second, called the build-up time, for the current flow and the magnetic field to reach their peak. This is due to the counter voltage induced in the winding by the increase of magnetism. The battery voltage, which forces the current through the primary winding, is opposed by the counter voltage.
Coil characteristics are so balanced with build-up time that, even at top engine speed when the contact points remain closed for the minimum time, the coil will build up sufficiently for good ignition. The amount of cam rotation between the closing and opening of the contacts controls the build-up time, and is known as the cam angle or dwell angle.
When the distributor contacts open breaking the primary circuit, the current attempts to continue to flow and tends to cause an arc across the points. The condenser prevents the arc by absorbing the sudden shock of the current caused by the opening of the contacts. Therefore, the magnetic field around the primary winding, induced by current flow, quickly collapses. It is this sudden collapse of the magnetic field that induces a high voltage in both the primary and secondary windings.
The voltage induced in the secondary winding causes current to flow through the coil to distributor cable, the distributor cap center contact and rotor to the brass contact lined up with the rotor at this time, then through the spark plug cable to the spark plug and across the gap of the spark plug electrodes to ground. The voltage induced is proportional to the turns of wire in the windings and the resistance at the spark plug gap. The induced voltage in the primary winding may be as high as 250 volts; and, consequently, the induced voltage in the secondary winding may go as high as 25,000 volts.
The voltage necessary to cause an arc at the spark plug gap is somewhere between 4,000 and 18,000 volts. The extra voltage represents the electrical reserve built into the ignition system. The voltage required to fire the plug varies with conditions including engine compression, engine speed, mixture ratios, spark plug gap, temperature, and many other conditions. These conditions must be taken into consideration when diagnosing ignition troubles and servicing the ignition system.
SERVICING THE IGNITION SYSTEM
Although good ignition is one of the requirements for good engine performance, it must also be remembered that good carburetion and good compression are equally essential. The ignition system is often blamed for engine failures and poor performance when the source of the trouble might be either the carburetor and fuel system or compression. To make a correct diagnosis, the procedure for checking the ignition system is outlined as follows:
1. Check the ignition primary and secondary wiring and connections. Replace any leads that are frayed, have broken strands, or have defective or deteriorated insulation. Clean and tighten all connections.
2. Check the distributor vacuum advance on the Six and Eight by rotating the complete distributor in the direction opposite that of the normal (counter clockwise) rotation of the breaker cam. To loosen the distributor, back off the screw on the spark retard/advance plate where the vacuum advance connects to the distributor. The distributor should turn freely and the vacuum advance spring should return the distributor to its original position. Another test is to disconnect the vacuum line at the carburetor and connect a vacuum/brake bleeder gauge. Pull vacuum, and the needle should stay steady at 20". If it falls, the vacuum advance diaphragm is bad.
On the Super Eight distributor, rotate the breaker plate clockwise to check the vacuum advance operation. The plate should rotate without binding. It should not wobble, and should return to its original position when it is released. On this type unit, be sure to check carefully the ground leads, known as "pigtail" leads, for fraying, broken strands, or broken terminal connections.
The centrifugal advance can be checked by rotating the breaker cam in the direction of its normal rotation. It should rotate freely and the centrifugal advance springs should return the cam and rotor to their original position without binding.
These quick checks indicate whether the advance mechanisms are working or not. However, for accurate testing of these units, the distributor should be removed and tested with a reliable distributor tester and instruments under various speeds and vacuum conditions.
3. While the distributor cap is off, wipe out the cap with a soft cloth. Inspect the cap and rotor for chips, cracks and carbon paths which would allow secondary current leakage to ground. Examine the contacts by holding them apart with the finger or thumb. Contacts that have been in service will not appear to be smooth and bright. This does not necessarily mean that they are not operating satisfactorily. On the contrary, they may be making contact over a greater area than could be obtained with new contacts. Clean the contact points with a fine-cut file. Blow out all dust particles. Make sure none remain on the contact surfaces. If the contacts are burned or pitted, they should be replaced.
Caution: Never use emery cloth or sandpaper to clean the contacts as the particles of these abrasives will be embedded in the contact surfaces and cause the contacts to burn. Use a point file instead.
4. Test breaker arm spring tension using the spring scale. The spring tension should be 19 to 23 ounces on the Delco-Remy distributor and 17 to 20 ounces on the Auto-Lite distributors. The correct tension may be obtained by shifting the breaker arm spring in its slot.
5. When the contacts require cleaning or replacement, remove the distributor from the engine, since the job can be done more easily and more accurately on the bench. Notice the position of the rotor and the distributor before removing it, so that it can be easily installed in the same approximate position and will require only a slight adjustment to complete the timing.
After the contacts are cleaned or replaced, adjust them by setting the cam angle using a feeler, to the correct opening of .020 inch on the Six distributor, and .017 inch on the Eight and Super Eight distributors. Be sure all contacts are aligned and have maximum contact area.
On the late-type distributors, the stationary contact is adjustable by loosening the lock screw and turning the eccentric screw for adjustment. The earlier type contacts are adjusted by loosening the lock nut and turning the contact in or out.
Whenever a synchroscope or some other good distributor tester is available, check the operation of the centrifugal advance throughout the entire distributor speed range. There are several reliable makes of synchroscopes and testers, any of which will test distributors satisfactorily.
6. After the distributor is tested accurately and the condenser is reinstalled, install the distributor on the engine with the rotor and distributor in the same position they were when the distributor was removed. Make sure the distributor is all the way down in its mounting and that the hold-down clamp or screw is tight. Be sure the vacuum line is tightened securely. Turn the grease cup in one turn. The ignition timing should then be adjusted correctly.
7. With the distributor cap removed and using the timing marks on the vibration damper to check crankshaft rotation, rotate the crankshaft in the direction of normal rotation until #1 piston comes up on the compression stroke with the intake and exhaust valves closed, and the marks on the vibration damper align with the pointer. Loosen the clamp screw and rotate the distributor base clockwise to advance the timing, or rotate it counterclockwise to retard the timing, until the breaker contacts just start to open with the rotor aligned with the #1 electrode of the distributor cap. Be sure to tighten the clamp screw when timing is completed.
The timing may be checked by means of a test lamp connected from the distributor primary terminal to ground. When the ignition switch is turned on, the light will not burn when the contacts are closed, and will go on just as the contacts break. Press the distributor cam lightly against the direction of normal rotation to remove all backlash.
An ignition timing light which operates on the current from the distributor to the #1 spark plug may be used to adjust ignition timing. By putting a chalk mark on the pointer and the correct timing mark on the vibration damper, the stroboscopic effect of the timing light with the engine idling will cause these two chalk marks to appear to line up when the ignition timing is correct. Caution: Be sure that the engine is idling no faster then 450 to 500 rpm when setting the timing with a timing light. An engine that is operating above 500 rpm may cause the centrifugal advance to come into operation and give inaccurate timing setting. With the correct timing, there may be a slight trace of spark ping when accelerating with wide open throttle from ten to thirty miles per hour in high gear.
8. Oil on the contact surfaces is the most common cause of burned contacts. The carbon formed by the burning of the oil will embed in the contact surfaces. This will cause the contact points to arc, and, consequently, to burn. Clean or replace the contact points and adjust the gap. Locate and eliminate the source of the oil. Do not over lubricate the breaker cam surface or the cam wick.
9. High voltage in the electrical system will cause excessive current to flow through the contacts. This results in a blue scale formation on the contact surfaces. When this condition is found, all electrical connections of the ignition circuit should be tightened and the voltage regulator should be checked and reset if necessary.
10. Inspect the insulation of the secondary ignition cables and the primary wiring for cracks, worn insulation, frayed insulation, and brittleness. Check the wires and cables for broken strands. Examine the terminals and connections for corrosion and looseness. Replace the wiring and clean, repair or replace the terminals if necessary.
11. The spark plugs should be inspected, cleaned and adjusted or replaced if necessary. Gap should be .028 inch and is adjusted by bending side electrode only.