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the movable electrode B into contact with the permanent electrode or spark plug A, and completing the electrical circuit. As the slide bar reaches its upward limit the

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Fig. 96.-Make-and-break Igniter (Operation)

screw G trips the dog from the plunger, and the latter on its downward travel brings the thimble against the rocker arm C and thus snaps the movable electrode B

away from the spark plug A, creating a sudden, hot spark between the two.

The igniter may be timed to advance or retard the spark by screwing the adjusting screw G either up or down, and may be still further adjusted by screwing

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up or down the spark plug A, or by loosening the set-screw that connects the rocker arm to the spindle and allowing it to set at a varying angle with the movable electrode. In the form of igniter illustrated the spark plug is screwed into the cylinder head, and the rocker spindle is inserted through the cylinder, enclosed in a bushing E. This form is in wide use, but it is often essential to remove the rocker electrode for repairs or cleansing and to do this requires considerable time and work. To overcome this difficulty several makers have adopted an igniter which is entirely self-contained in one piece, and which bolts onto the cylinder with its inner portion projecting inside. Such an igniter is illustrated in Fig. 98, in which the lettering is the same as already described and identical with that in Fig. 40. The make-and-break system has the advantage of being practically water-proof, for it is operated by a lowtension current and is free from short-circuiting troubles. For this reason it is a great favorite with fishermen,

Fig. 97.-Make-andbreak Igniter

lobstermen, and other users of open boats; but its disadvantages in my mind more than offset its good points. The sparking points of the two electrodes frequently become foul with dirt or soot and the low-tension spark is not sufficiently hot to burn this off as in the jump-spark plug.

The continual banging or hammering together of the two electrodes soon wears away the points, necessitating

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Fig. 98. Self-contained Igniter

frequent renewal and adjustment; the spindle of the rocker arm often becomes gummed or stuck with oil or rust, causing missfires or breaking of the spindle or rocker; the set-screw holding the rocker to the spindle often breaks or wears loose, allowing the rocker to work

on the spindle without operating the interior electrode; springs lose their strength or break; and the mica insulation of the spark plug often breaks, or becomes so filled with oil and soot that it fails to act as an insulation. In addition to all these defects the make-andbreak system is very noisy and dirty and requires constant care and attention. Many make-and-break

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Fig. 99.—Make-and-break Igniter Altered to Jump-spark

motors that are practically worn out may be given a new lease of life by converting them into jump-spark motors. This is usually very easy and inexpensive. If the igniter is of the external type illustrated in Figs. 40, 96, and 97, it is only necessary to remove the rocker and spindle and plug the hole; remove the plunger, plunger spring, thimble, and rocker spring. Fasten a piece of fibre to which a terminal and spring is attached -to the slide guide and replace the make-and-break

plug with a standard jump-spark plug. This transformed igniter is shown complete in Fig. 99. The dog on the slide bar coming into contact with the spring A makes the electrical connection and causes a spark in the cylinder. By placing an adjusting screw through the fibre block B, as shown in C, the spring may be pressed up or down at will, thus retarding or advancing the spark. In the case of motors having a rotary pump, or provided with a self-contained igniter, it is often easier to attach a regular timer to the pump shaft or to a special shaft operated by gears on the engine crank shaft. Of course in any case where the system is changed from the make-and-break to the jump-spark it is necessary to substitute a vibrator coil for the primary coil used in the old make-and-break arrangement.

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