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trouble is due to a broken connection inside of the coil box or the contact points do not touch. If the vibrator operates as it should and there is an extremely bright spark between the points and a weakened secondary spark, it is reasonable to assume that the condenser inside of the coil box is ruptured.

If there is a proper vibration or buzz at the vibrator and no secondary spark from the high-tension terminal, the trouble is either a broken high-tension connection or a short circuited secondary winding. Sometimes a wire inside of a coil is twisted off where it fastens to the terminal screw, due to that member being turned around several revolutions with a pair of pliers. A case of this kind may be fixed by removing the bottom or top of the coil box, as the case may be, and making sure that the connection is resoldered to the terminal post. A punctured winding or short circuited condenser can only be repaired by the coil manufacturer, and in most cases it is 'cheaper to procure a new coil unit, which is easily removed in modern coils, than to attempt to have the old one repaired.

When a coil unit is suspected of being defective it is easy to ascertain if this is the case by changing it for one of the coil units which is known to be in good condition. If the cylinder which was formerly served by the good coil unit now begins to skip, one may assume that the coil unit is at fault. If the trouble has not been due to other causes, the cylinder that was formerly at fault will begin to operate as it should as soon as the spark plug is connected to the good coil unit which has been substituted for the one thought to be defective.

Adjusting Coil Vibrators.—The repairman who understands the vibrating spark coil is the exception rather than the rule. Many are able to adjust a vibrator, but do not know how to locate troubles, or to remove the exposed component such as the bridge, vibrating spring, etc., and reassemble the parts correctly. If the vibrator buzzes weakly when contact is made at the timer, the first thing to do is to test the battery to make sure that there is sufficient current available to operate the vibrator, then the contact points should be examined to see that they are clean and smooth. Various defective conditions are shown at Fig. 83, A; any one

of these will interfere with correct contact and with proper vibrator action. At A-1 a pit has been burnt in the lower point and a projection has been built up on the upper one. At A-2 the points have been cleaned with a file which has been inserted at an angle so the contact members do not have a true flat surface. At A-3 a point has been built up on one side of the contact of both vibrator springs and contact screw points. As these contact points

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Fig. 83.—Methods of Cleaning Induction Coil Vibrator Contact Screws.

are of platinum it is important to remove as little of that valuable material (which is now worth more than gold) as possible.

For this reason it will be desirable for a repairman working on cars using vibrator coils to provide himself with the simple fixture shown at Fig. 83, B, which insures that the points will be. dressed true without removing much material. The fixture is a simple U-shaped piece of hardened steel having a series of holes, A, B, C. drilled into it of such size as will permit the insertion

of the most commonly used sizes of vibrator adjusting screws. These are not threaded, the screw F being a free fit in the hole corresponding to the outside diameter of the thread. A feed screw E may be interposed under the adjusting screw in order to feed it up against the smooth file used to clean off the roughness. This screw may be shifted into any one of the tapped poles under the holes A, B and C for feeding different sized contact screws.

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The conventional vibrator is shown at Fig. 83, C, and another form at Fig. 84. It will be noticed that this consists of a vibrator spring or armature carrying one contact point and a bridge member over it carrying another contact which is set into a knurled head adjusting screw in that at Fig. 83, C. The smaller bridge holds the vibrator spring and is also provided with a knurled screw so the vibrator spring tension may be adjusted. Directly under the vibrator is the iron core which attracts it to break the contact between the points. The farther away the vibrator is from

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

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