so equipped. When a magneto is employed in connection with two spark ignition it is common practice to provide two separate distributors and in some cases a double wound armature having two sets of windings served by a common contact breaker. In the system shown at A, Fig. 116, a two spark magneto is employed

in connection with the simple dash switch wired as indicated, by which one may obtain the use of but one spark with the switch lever in the position shown and the double spark if the switch lever is rocked to the other extreme, or on the line marked "2." If the lever is swung to the left or on a line with that indicated "O," no spark will pass through the engine, as the magneto will

be grounded. The system outlined at B is that of a two spark magneto that can be used in connection with a vibrator coil and battery, as in the dual system previously described. In addition to the switch on the coil, a two point switch is placed on the dash in order to obtain single or double spark ignition as desired.

Magnetic Spark Plug Systems. Other low tension ignition systems have been devised though they have never received wide application in which the moving mechanism needed to operate the igniter plates from the camshaft have been replaced with magneti

cally operated spark plugs, the leading example of which is the Bosch shown at Fig. 118, A. This consists of three main parts, a supporting member which screws into the spark plug hole in the combustion chamber, an electro-magnet and oscillating mechanism. The electro-magnet contains a coil of wire D, and is protected by a cover B, and iron outer shell A. A cylinder H which is threaded at its lower end projects into the coil. A collar R forms the base of the magnet. The oscillating mechanism consists of a pole piece E, a horse-shoe shaped spring G, and an armature F. The lower part of the pole piece is provided with threads to fit the

hollow cylinder H, and is formed externally to be retained in the support K by a retaining nut or collar L. The supporting member has the upper half of hexagonal form the same as any spark plug body and is threaded to fit the spark plug aperture. A steatite insulating member J in connection with the packing gasket insures against loss of compression or explosive pressure.

The operation of the plug is very simple, as when the terminal P is connected to the scurce of current when the electricity passes

Wiring at B.

through the coil it magnetizes the core E, which attracts the armature F, pivoted on a knife edge extending from E to the right, this separating the contact points M and N and producing a spark. A brass plug O is inserted in the core E so the armature will not stick to the pole piece due to magnetism. A spring G tends to keep the points M and N in contact. The point N is attached to the spark plug body and is V shaped, the other point on the armature being formed to fit into the V portion of M.

The complete ignition system is shown in diagram form at Fig.

118, B, and is very much the same as the wiring for a high tension magneto using jump spark plugs. In addition to the timer or contact breaker which is of the usual form, the magneto must include a distributing device which will allow the circuit to flow to the plug in the cylinder about to fire a charge. The distributor consists of four contact points carried by a body member of insulating material and a rotary distributor arm that makes contact with the different contact points in turn according to the firing order of the engine. The principal trouble apt to occur with the magnetic plug is short circuiting due to carbon deposits or accumulations of oil which will interfere with prompt action of the oscillating armature F. If the spring G breaks, the operation of the plug will be erratic and the engine will misfire. This system has received but limited application on automobile engines, but has been used to some extent in marine engine work so the repairman should, at least, be familiar with its principle of operation in order to have a reasonably complete knowledge of electrical ignition methods.

Impulse Starters.-Special forms of couplings, as illustrated at Fig. 119, may be used to drive the magneto armature. This provides a hot spark even when cranking slowly, as the armature speed is accelerated by a spring arrangement so the speed approximates that obtained when the engine is turning over under power. The device illustrated is known as the Eisemann impulse starter coupling. This may be attached to any model of Eisemann magneto and is said to have no effect upon its regular operation except at slow speeds, when it causes the armature to rotate in a series of jumps instead of at a uniform speed. These jumps cause the armature to cut the lines of force of the magnets quickly, or at the same speed that it does when the motor is revolving swiftly, so that a hot spark is generated. This removes any necessity for auxiliary battery ignition for starting on heavy duty motors, for a hot fat spark is generated at any speed, regardless of how slowly the crank is turned. The coupling consists of a driving tube A in the center and a driven cup B inclosing the device, the two being connected by a spring. Within the driven cup is a loose ring C, known as the trigger, this ring having a lip which extends

through a slot on the periphery of the cup. At the bottom of the coupling is a notched bar, so positioned that as the cup revolves the notch registers with the slot in the cup, so that the trigger lip drops down by gravity and thus locks the cup against rotation. This is the position shown in the view at C. On the outside of the trigger ring is a cam which engages a corresponding cam cut in

the driving tube. When the lip has engaged the notched bar and the cup ceases to rotate the driving tube continues to turn. This turning compresses the spring which is seated against a driving pin on the tube and a block fixed to the cup. At a predetermined point the cam on the trigger ring engages that on the tube, and lifts the