The operating principle of the Atwater Kent ignition system type K-2, differs from type CC system in that it operates on the open circuit plan, whereas the type CC system explained in the preceding chapter, operates on the closed circuit plan.

A-K ignition system type K-2 consists of three parts:

No. 1. The unisparker combining the special contact maker, a condenser, and a high tension distributor.

No. 2. The coil, consisting of a simple primary and secondary winding, and a condenser. These parts are all imbedded in a special insulating compound. The coil has no vibrator or other moving parts.

No. 3. The ignition switch. This switch controls the system by opening and closing the primary current.

The Principle of the Atwater Kent System.—The function of this system is to produce a single hot spark for each power impulse of the motor. It differs from other types of battery ignition systems in that the contact points do not touch except during the brief instant of the spark. The ignition circuit is, therefore, normally open, whence the name “open circuit” results. The contact maker consists of a pair of contact points, normally open, which are connected in series with a battery, and the primary circuit of the non-vibrating induction coil. The mechanism for operating the contacts consists of a notched shaft having one notch for each cylinder, rotating at one-half the engine speed, a lifter which is pulled forward by the rotation of the shaft, and a coil spring which pulls the lifter back to its original position after it has been drawn forward and released by the notched shaft; hardened steel latch, against which the lifter strikes on its recoil and which in turn operates the contact points.

Operation of the Contact Maker.—It will be noted in Fig. 71 that the lifter is being pulled forward by the notched shaft. When pulled forward as far as the shaft will carry it (Fig. 72), the lifter is suddenly pulled back by the lifter spring. In returning, it strikes against the latch, throwing this against the contact spring and closes the contact for a brief instant. This movement is far too quick for the naked eye to follow (Fig. 73).

Fig. 74 shows the lifter ready to be pulled forward by the next notch.

Note that the circuit is closed only during the brief instant of the spark. No current can flow at any other time, not even if the switch is left on when the motor is not running. No matter how slow or how fast the notched shaft is turning, the lifter spring will always pull the lifter back at exactly the same speed, so that the operation of the contact, and therefore the spark, will always be the same no matter how fast or how slow the engine is running. The brief instant that the contact points touch, results in very little current consumption. The high tension current from the coil is conveyed to the rotating distributor block, which seats on the end of the unisparker shaft to each of the spark plug terminals in the order of firing.

The important advantage which the distributor possesses is the fact that there are no sliding contacts or carbon brushes. The distributor blade is so arranged that it passes close to the spark plug terminals without quite touching (as shown in Fig. 75), thus permitting the spark to jump the slight gap without any loss of current pressure. This also eliminates all wear and trouble caused by sliding or rubbing contacts.

Fig. 76 shows the wire connections and direction of current flowage. The distributor blade is about to make contact with the terminal leading to the spark plug in No. 2 cylinder. At the instant that contact is made the breaker points in the contact maker shown in the lower part of the diagram close, thus allowing a primary or low tension current to flow between the contact maker, coil, and battery. The sudden breaking of this current occurs when the points open again, thereby creating a current of high tension voltage in the secondary coil which is conducted to the center terminal of the distributor where it is distributed to the spark plug terminals through the rotation of the distributor blade. The high tension cables leading from the distributor are heavily insulated, thus the current in seeking ground return chooses the easiest path, by jumping the slight gap at the spark plugs.

Setting and Timing the Unisparker.—The type K-2 unisparker is installed, so as to allow a small amount of angular movement or, in other words, the socket into which the unisparker fits is provided with a clamp which will permit it to be turned or locked in any given position.

Timing.—The piston in No. 1 cylinder is raised to high dead center between the compression and power stroke. Then loosen the clamp which holds the unisparker and turn the unisparker backward, or contrary to the direction of rotation until a click is heard. This click happens at the exact instant of the spark. Clamp the unisparker tight at this point being careful not to change its position. Note that current for this system is usually supplied by the starting and lighting battery. When changing batteries be sure that the voltage of the battery is the same as that marked on the coil.

The external wiring of the A-K type K-2 is very simple, as shown in the diagrams, Figs. 77 and 77A. Fig. 77 shows the wire connections, when the reversing switch and under-hood coil is used. Fig. 77A shows the connections, when using plate or kick switch coil. A well insulated braided primary wire is used for the primary or battery circuit. See that this wire is well protected against rubbing or abrasion wherever it comes into contact with metal parts of the car. When the starting and lighting battery is used to furnish the ignition current, two wires should run directly to the battery terminals.

The two types of Atwater Kent systems described are provided with automatic spark advance mechanism. Provisions are also made for manual lever control, by simply connecting the unisparker to the throttle lever at the base of the steering gear.

Fig. 78 shows the automatic spark advance mechanism. It is located on the underside of the contact maker base plate, and consists of a set of weights which swing out from the center against spring tension, and advances the unisparker on the shaft, according to the amount of centrifugal action or speed of the shaft. When the shaft is not in motion the springs draw the weights toward center, which automatically shifts the unisparker on the shaft until the spark is in a fully retarded position.

Contact Point Adjustment.—The only adjustment aside from the initial timing is in the contact points. They are adjustable only for natural wear, and one adjustment should last at least six months. The contact screw is provided with a number of shim washers against which it is set up tight. When the points eventually become worn, they should be dressed flat and smooth. A sufficient number of the washers should be removed so that when the contact screw is set up tightly it will maintain the proper gap between the points. The distance between the contact points should be about the distance of a thin visiting card. They should never touch when at rest.

Fig. 79 shows an oiling diagram of the contact maker. The latch, lifter, and lifter spring are not adjustable or subject to wear. They should be well cleaned and oiled every five hundred miles. Use a light oil and avoid getting it on the contact points.

The Condenser.—The condenser of this system acts somewhat like a shock absorber to the contact points. It absorbs the spark or arc and makes the break in the primary current, clean and abrupt. The condenser is very accessible, but should never be tampered with, as it does not require any attention.

Testing for Ignition Trouble.—If the engine misses without regard to speed, test each cylinder separately by short circuiting the plug with a screw driver, allowing a spark to jump. If all cylinders produce a good regular spark the trouble is not with the ignition system.

If any cylinder sparks regularly this will indicate that the ignition system is in working order so far as the unisparker and coil are concerned. The trouble is probably in the high tension wiring between the distributor and plug, or in the plugs themselves. Examine the plugs and wiring carefully. Leaky secondary wiring is frequently the cause of missing and backfiring.

Frequently, when high tension wires are run from the distributor to the spark plugs through a metal tube, trouble is experienced with missing and backfiring, which is due to induction between the various wires in the tube. This is especially likely to happen if the main secondary wire from the distributor to the coil runs through this tube with the spark plug wires.

Whenever possible the distributor wires should be separated by at least one-half inch of space. They should be supported by bracket insulators, rather than run through a tube. In no case should the main distributor wire run through a conduit with other wires.

If irregular sparking is noted at the spark plugs, examine the battery and connections.

If the trouble commences suddenly, it is probably due to a loose connection in the wiring, if gradually, the battery may be weakening or the contact points may require attention.