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Fig. 36.—Diagrams Explaining Action of Atwater-Kent Contact Breaker.

slight gap that exists between them. Owing to there being no actual contact, there will be no depreciation in the distributor or upper portion. The center terminal, which is in connection with the induction coil, is a combination of carbon and brass, and a light, flat spring on the quadrant bears against it to maintain positive electrical connection. The distributor cover is easily removed without the use of tools, as it is held by spring clips. Location or dowel pins in its lower edge insure that it will be replaced in the correct position.

One of the most popular of the combined starting, lighting and ignition systems is the Delco, which is shown at Fig. 37. For the present we will concern ourselves merely with discussing the ignition functions of the system, leaving the self-starting and electric lighting features for more comprehensive consideration later. Current is produced by a one unit type motor-generator, although the windings of the device when operated as a motor or a generator are entirely separate. The ignition current is obtained either from a storage battery, which is kept in a state of charge by the generator, or from a set of dry cells which are carried for reserve ignition. The ignition system consists of a one unit nonvibrator coil, sometimes attached to the top of the motor generator, though it may be placed at any convenient part of the car and a dual automatic distributor and timer usually included as a part of the device as shown. When ignition current is supplied from the lighting circuit the current passes from the storage battery through a switch and out to the low tension winding of the coil, from whence it passes to the timer and from there to the frame, where it is grounded. The high tension current generated in the coil runs to the distributor, where it is switched to the spark plug in the different cylinders in turn.

When dry cells are used for ignition the operation is the same except that a device called “the ignition relay," and shown at the right of Fig. 38, is added to the circuit. The function of this device is to break the circuit immediately after it has been completed by the contact points of the timer, which is shown at the left. The use of the ignition relay results in a material saving of the battery current as the circuit is closed a much shorter time than is the case when the circuit is broken by the timer contacts themselves. The operation of the relay is not difficult to understand. The magnet A attracts the armature B when the circuit is completed through the timer. This action opens contact C and

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Fig. 37.—The Delco One Unit Starting, Lighting and Ignition System.

breaks the timer circuit. A condenser D is mounted besides the magnet coil A, in order to absorb the current produced by selfinduction in the magnet winding, which would be apt to produce a hot spark between the contact points when they were separated if no means were taken for its disposal. The adjustment of the relay is at the pole piece E. This regulates the distance between the armature B and the magnet pole, and the gap between the contacts C. The adjustment is made by turning the notched head at E clockwise to increase, anti-clockwise to decrease, the gap between the contacts. The correct distance between contacts C when the armature B is pressed down is equal to approximately the thickness of one sheet of newspaper. A very simple way in which the adjustment can be made when the engine is running on the battery is to turn the notched head of the pole piece in the counterclockwise direction until the motor ceases to fire. Then turn it four or five notches in the opposite direction. Under no conditions should the adjustment screw be turned very far in either direction. If the armature vibrates feebly when the starting button is pressed it indicates either weak dry cells or dirt between the relay or timer contacts.

The interior arrangement of one form of timer for both dry cells and storage battery current is shown at Fig. 38. The cam C is driven by a rotating shaft and establishes contact between the points when the cam rider rises on the point of the cam. When the cam rider drops into the notch between the high points the contact points separate. The same instructions that have been given for the contact points of the Atwater-Kent timer apply just as well in this case. While the contact points are but one-eighth inch in diameter, it is said that many thousands of miles of service may be obtained without readjusting. It is important that the contact spring, which is the straight one carrying the platinum point, should have a good tension outward against the cam rider member below it. It is said that this spring should be capable of supporting the weight of half a pound. If the tension is not sufficiently great the contact points barely break contact which permits the spark to arc between them, tending to burn them. The contact should be so adjusted that the contact spring is forced away from the breaker member at least half the distance of the T-slot on the vertical part of the cam rider, when the latter is on the contact lobe of the cam. The contact points should open about ten one-thousandths (.010 inch) inch when the contact arm rests upon the back stop. The contact arm should clear the cam except at the contact lobe.. A short wire connects the two posts

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Fig. 38.-Delco Primary Timer at Left and Ignition Relay at Right.

of the breaker arms and this connection should always be inspected when making adjustments to insure that it has not been disturbed. It is said that if this wire is disconnected the current will pass through the contact spring, impairing its tension. Whenever the contact points are cleaned care should be taken to have the sur. faces parallel.

In some of the Delco ignition systems an automatic spark advance mechanism is used. The usual method of wiring when the distributor is a separate member from the generator is shown at A, the left of Fig. 39. The construction of the automatic spark advance mechanism is shown at B. In this the shaft which trans

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