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wire which lear's to the bus bar or to the insulated terminals of the igniter plate is connected to one of the terminals of the coil so the winding of the coil really forms an extension of the conductor leading to the igniter plates. The other battery terminal is connected to the ground through a simple form of switch.

Q. Describe construction of igniter plate.

A. A typical igniter plate which has been used successfully on many Locomobile cars is shown at Fig. 102. The view at 1 shows the exterior of the plate which is approximately triangular in form and which has three projecting lugs by which it is bolted to the combustion chamber. The interior view is shown at 2, this showing the movable hammer member, which is rocked by the simple lever extending to the tappet rod operated by the camshaft. The combination of hammer and operating lever forms a bell-crank provided with a suitable journal in the igniter plate so the hammer member can rock back and forth and establish contact with the fixed insulated member which is called the “anvil” and which is shown detached from the igniter plate at 3. The hammer is provided with a platinum contact point which normally rests against a similar contact member on the stationary anvil.

The wire conveying current from the magneto or battery is attached to the fixed terminal or anvil insulated from the main body portion of the igniter plate. The plate shown is provided with a taper joint, so that it makes a gas tight connection when inserted into the opening made to receive it in the combustion chamber wall.

The method of operation of the igniter plate is clearly outlined at Fig. 103-A. As will be seen the cam lifts the roller on the tappet rod plunger and establishes the circuit which is broken as soon as the roller rides off of the point of the cam and the contact points at the gniter plate are separated.

In the diagram at Fig. 103-B the various parts of the igniter plate operating mechanism are clearly outlined. The main current conveyer or bus bar 1 is brought into electrical connection with the insulated terminal 6 and the anvil carried in plate 3 by means of the switch lever 2. The grounded hammer member 4 is operated by the external lever 5 which establishes contact between the hammer 4 and the anvil 6 when it is raised by the rod 9 which applies

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its pressure through the medium of the spring 8 as the roll carrying plunger 11 is raised by the cam member in the guide bushing 10. When the roller carrier 11 drops off the point of the cam, the rod 9 is pulled down and the hammer 4 is separated from the anvil 6 by means of the nut 7 at the end of the rod 9. The spark time is advanced and retarded by sliding the igniter operating camshaft along so that the roller on the member 11 is raised sooner or later depending upon its position with reference to the inclined cam point.

Q. Is coil needed with magneto on low tension ignition system?

A. As the magneto armature may be wound with sufficient

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Fig. 103.—Showing Action of Locomobile Low Tension Igniter Plate.

wire to produce a hot energetic spark a current of sufficient intensity may be produced directly from the mechanical generator without the use of a "kick-coil” such as necessary with a battery.

Q. Must magneto be timed?

A. The armature of the magneto must be timed with a certain definite relation to the crankshaft of the motor because the igniter points separate in the combustion chamber only when the magneto armature has attained that portion of a revolution where the current generation in the armature winding is at its maximum value. This means that the magneto must be driven by positive means from the engine crankshaft, and on a four cylinder engine the magneto armature runs at crankshaft speed just as in the high tension forms.

Q. What are the advantages of this system?

A. It is claimed that the low tension system of ignition is not affected by water as is the high tension form with exposed.spark plugs and that it will produce a hotter spark than will the high tension system. It is widely used in marine and stationary installations but is seldom employed at the present time on motors intended as automobile power plants.

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Q. How many types of high tension ignition systems are used?

A. Two main forms of high tension systems are used, those in which the current is generated by a magneto and the others which use chemical current producers to generate the electrical energy which must be intensified by means of transformer coil before it can be directed to the plugs.

Q. Describe action of simple induction coil, timer, and battery system for single cylinder engines.

A. The arrangement of the parts of a simple, high tension ignition system has been previously considered and is clearly outlined at Fig. 77-A. The current is supplied by means of a storage battery or a six cell dry battery, as desired. The positive terminal of the dry battery group and that of the storage battery are joined together and are connected with the ground which may be any point on the metal frame of the engine. The wire from the zinc terminal of the dry battery group goes to one side of a two point switch while the negative terminal of the storage battery is connected to the other side of the switch. Either the dry or storage battery may be brought in circuit with the induction coil and timer by moving the switch lever to one side or the other.

The timer is a simple form having one insulated contact segment which is connected to one of the primary terminals of the coil. The other primary terminal of the coil is connected to the switch lever while the secondary coil terminal is connected to the insulated terminal of the spark plug by means of a well insulated high tension cable. As the crankshaft of the engine revolves, it turns the revolving contact member of the timer and when the piston reaches the proper position in the combustion chamber the roll on the revolving timer member makes a contact with the insulated segment carried by the timer case. Assuming that the switch lever is on the storage battery contact button, the current will flow from the positive terminal of the storage battery to the ground on the engine base and from thence through the medium of the metal parts of the engine to the revolving timer brush, which is in metallic contact with the engine camshaft, and which, therefore, transmits the current through the insulated segment to the primary terminal of the spark coil, because of the connection or wire joining these two parts.

When the current passes through the primary winding of the coil it produces a secondary current in the high tension winding as has been previously explained and passes out of the coil box through the primary terminal which is joined to the switch lever and from that point back to the storage battery through the switch lever and the wire connecting the battery with the switch. As long as the engine revolves a contact will be established at the timer every two revolutions of the crankshaft and a current will flow from the batteries through the primary winding of the coil and back again to the battery. Each time a primary circuit is established at the timer a spark will be produced at the spark plug points and the gas compressed in the combustion chamber by piston will be exploded.

Q. Outline action of induction coil, timer, and battery system for four cylinder engine.

A. The action of the four cylinder ignition system outlined at Fig. 100 is exactly the same as that previously described. Instead of a single unit coil a spark coil assembly having four units, one for each cylinder, is employed and a timer is used that has four insulated contact segments, one for each cylinder of the engine. As the timer contact revolves it makes an electrical connection with the various insulated segments in turn so that the various primary windings are energized when a spark is desired in the cylinder that is to be fired, depending upon the firing order. In the group shown at Fig. 100, a spark takes place first in cylinder No. 1, then in cylinder

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