the core the more current will be needed to actuate the vibrator. The spring tension should be sufficient, so that the trembler will vibrate fast enough to produce a pronounced buzzing sound. If the vibrator spring lacks elasticity, too much current will be consumed which is an important item if the current for ignition is derived from a dry cell battery. In adjusting the coil vibrator it is not necessary to turn the motor over to establish contact as the tuning up may be readily performed on most coils by connecting a wire to the steering post as shown at C, and touching the knurled head of the adjusting screw or the bridge carrying it with the other end of the wire. It is necessary, of course, to have the switch on the coil in the "on" position. Another method of accomplishing this is to short circuit the timer with a screw driver as shown at B, which is used to bridge the wire terminal and the aluminum timer case. In this way each of the vibrators may be made to buzz in turn. If the points are not too badly burnt it is possible to clean them with a piece of very fine emery cloth as shown at Fig. 83, B, without removing either vibrator or contact screw from the top of the coil. Where battery current is used it is well to test the current consumption of the coil from time to time as the vibrators are adjusted. It is possible to have a coil draw twice as much as needed if the vibrator spring tension is too great. The current consumption will vary from .5 to 2.2 amperes, a fair average being about 1 ampere. The usual primary voltage needed is 5 or 6, and the trembler vibrations will vary from 100 to 400 per second. If the vibrator tends to stick, the core should be filed off as well as the undersurface of the vibrator to remove any rust that may be present between the surfaces. A projecting core wire sometimes interferes with proper vibrator action. Make sure the top of the core is smooth and bright.

Roller Contact Timer Troubles.-When a timer of the roller contact form is used, ignition is apt to be irregular should the spring attached to the free end of the roller arm break. If the interior of the device is filled with dirty oil, the current is apt to be short circuited. If the device has been oiled with a lubricant having too much body, the roller is not apt to make good contact with the metal segments and ignition will be erratic. De

preciation in the bearing pin on which the roller rotates or of the fulcrum pin on which the roller arm swings will also result in irregular ignition. If the motor runs steadily at low speeds but misses fire at high speeds, and the trouble has been traced to the timer, it is necessary to feel around the inside of the fiber ring with the finger to see that this is smooth and perfectly round, and that the contact block faces are flush with the surface of the ring. If the blocks are worn below the surface of the ring, the roller is apt to jump the space at high speeds, due to the low block, and not establish an electrical contact. At low speeds the tension of the spring is sufficient to keep the roller bearing against the contact blocks, as it will follow the irregular contour of the timer interior without difficulty. If the segments are badly worn and the fiber ring roughened, the timer casing should be chucked in a lathe or grinding machine and the interior ground smooth and perfectly round with a small emery wheel. The writer has seen some mechanics attempt to take a light chip out of the timer interior, as they were ignorant of the fact that the contact blocks were of tool steel and hardened. A fast-running, free-cutting emery wheel is the best tool to use for smoothing down hardened steel segments. The stem or bolt attached to the contact block must pass through a fiber washer or bushing in order that it be insulated from the timer body. If these bushings crack, there may be an opportunity for leakage of current, especially on the Ford car, where the ignition current is derived from the magneto and is stronger than that usually produced by a chemical battery.

Wiring Troubles and Electrostatic Effects.-The principal troubles that are apt to occur in the wiring systems are evident on inspection, these consisting usually of a break in the conductor, which may sometimes be concealed by perfect insulation covering; wearing away of the insulation due to abrasion between the wire and some metal portion of the car which eventually results in a short circuit and the wiring becoming oil soaked and failing to properly carry the charge of current which leaks through the defective insulation. The wiring of a complete dual ignition system in which two radically different methods of ignition are used

is shown at Fig. 85. One system consists of a set of low tension igniter plates mechanically operated from a suitable camshaft, the other method, which is independent, has high tension ignition plugs operated through a timer of the usual form. At the present time where dual ignition systems are provided the usual practice is

to use two high tension systems, one of which will derive its current from a battery and coil, the other which will receive the energy of a high tension magneto. A typical double system adapted for six cylinder engine ignition is shown at Fig. 86. In this two spark plugs are carried in each cylinder, one over the intake, the other over the exhaust valve. A battery timer is mounted close to the dash from which six primary wires go to the

individual coil units of the coil box. High tension wires come from the bottom of the coil to one set of spark plugs. Another set of high tension wires extends from the magneto distributor to the remaining set of spark plugs.

It will be apparent that in both of the systems shown that considerable care is taken to have the wiring carried in an orderly. manner and kept out of contact with the metal portions of the

Fig. 87.-Methods of Insulating and Supporting Secondary Cable As

sembly.