Last month's article was on my 1946 Packard Standard 8, 282 CID (see archives section). The problem is loss of power at full throttle with backfiring. 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.
Next month we will continue exploring the ignition system, and in the meantime, enjoy your cars, keep 'em driving, and Merry Christmas from us to you!