The Gasoline Motor

by Harold Whiting Slauson

Thus it is with the ignition current. It can "tickle," rather viciously, sometimes, as many persons will aver, but the amount of electricity involved is so slight as to render the high pressure harmless. Nevertheless, it is well to avoid allowing the fingers or the arm to become a part of the high-tension circuit, for the result may be startling as well as annoying.

But in order that the high voltage shall be induced in the secondary coil, the primary circuit must be alternately made and broken between one stroke and the next. Consequently proper "piling up," or "surging," of the current will be effected. This is accomplished by means of an "interrupter" that either vibrates rapidly or "snaps" once at the formation of each spark. The former is the more common type used with battery ignition and is known as a vibrating coil. A circuit breaker is generally incorporated in the mechanism of a magneto, and consequently when such an instrument is used, the vibrator on the coil is dispensed with. It is the vibrator on each coil that forms the "buzz" that can be heard whenever the box cover is removed, and that often furnishes a simple test for determining the condition of the ignition system of the particular cylinder with which that coil is connected.

The vibrator is a flat, spring steel piece that rests near one end of the soft iron core around which the primary coil is wound. The springy nature of the vibrator ordinarily holds it against a small, adjustable contact point that should be set about an eighth of an inch from the end of the above-mentioned soft iron core. The primary coil is so wired that its current passes through the vibrator steel and the contact point against which it rests. As soon as the current travels through the coil surrounding the soft iron core, however, the latter becomes magnetized and draws the steel vibrator toward it. This breaks the circuit, the magnetism of the iron core disappears, and the vibrator returns to its original position against its contact point. But this action again forms the circuit, and the same operation is repeated as long as the current is allowed to flow toward the coil.

This is the same principle on which an electric bell is rung, but the vibrator of the coil makes and breaks the circuit much more rapidly on account of the less weight of the moving parts. This vibration of the coil interrupter is so rapid—hundreds a second probably—that the resulting spark is practically continuous and shows no effect of the breaks in the circuit.

Even though it is the primary current, of low voltage, that is interrupted by the vibrator, the frequency of these interruptions causes a slight sparking, or arcing, at the contact points. These are therefore subjected to rather a high degree of heat, as well as a large amount of wear, and it is necessary that they be made of a material that will resist both. Platinum has been found to be unusually suitable for this purpose, but owing to its high cost, only a small amount in the form of two points, or "buttons," is used. One of these points is placed in the vibrator steel, and the other is embedded in the end of the screw against which the first rests. Thus the actual contact is made against these heat-and-wear-resisting platinum points, and it is evident that upon their proper action depends the formation of the spark in the cylinder with which that particular vibrator is connected.

Notwithstanding the fact that platinum possesses high heat-resisting properties, the constant arcing at the contact points will eventually form a sort of corrosion in which minute particles of the material are carried from one point to the other in the direction in which the current flows. If the current is reversed, the corrosion will take place in the other direction, and consequently the platinum point that formerly lost a part of its material will gradually be "built up" again. This corrosive action is known as "pitting," and while it may be reduced to a certain extent by reversing the terminals of the battery, as described, the platinum will occasionally require additional attention.

A coil having badly pitted contact points on the vibrator will "stick" and will cease to form a spark regularly. It is often difficult to distinguish between trouble arising from badly-pitted contact points and that caused by weak or nearly-exhausted batteries, as either ailment produces the same symptoms of irregular running and "jerking" in the motor. For this reason, a volt and ampere meter for measuring the pressure and amount of the current delivered by the batteries should form a part of every automobile owner's tool equipment.

It is the amperage, rather than the voltage, that is reduced through continued use of the batteries, and when this quantity falls below nine or ten, the cells should be discarded—or recharged, in the case of a storage battery. But if the ignition occurs irregularly when the batteries are delivering the proper amount of current, it is probable that the trouble lies in the pitted condition of the platinum contact points of the vibrator of the coil. Fine emery cloth rubbed over the surfaces of contact should serve to remedy matters. It should be made certain that the resulting surfaces on the platinum points are not only rubbed smooth, but level, as well, in order that the entire area of each will rest in contact and the current will not be concentrated at a small portion.

It is probable that there will be a screw adjustment on the vibrator by means of which the force with which the latter rests against its contact point may be regulated. If the vibrator is set too tight, an undue amount of current will be required to magnetize the core of the coil sufficiently to pull the vibrator away from its contact point, and the batteries will soon "run out." On the other hand, the tension of the vibrator should be sufficient to enable it to spring away from the core of the coil as soon as the circuit is broken, for otherwise the vibrator will lag and will not be as "lively" as is necessary to obtain the best results.

The contact screw should be set so that the vibrator rests about three-thirty-seconds of an inch from the end of the magnetic core. After the tension of the vibrator has been set to approximately the proper amount, the ear must be trusted for the correct adjustment of the contact screw. When the switch is thrown on and the motor turned until current flows through the coil, the resulting buzz emanating from the vibrator should be decided and forceful. If this buzz is exceedingly high-pitched, it is an indication that the vibrator has been set too tight, and its tension should be loosened if unscrewing the contact point slightly does not lower the tone. It must be remembered that the tension of the vibrator can be changed by turning the contact screw. If this screw is turned down so that it forces the vibrator toward the iron core, the tension will be greater than will be the case if the contact point is turned to the left.