FORD VAN POINTERS.
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By R. T. Nicholson (Author 'of "The Book of the Ford").
TEE "mag," is often suspect, and is rarely faulty. When, however, "the engine won't start," the usual conclusion is that "the wag. isn't giving enough current,"
To set this unworthy doubt at rest, if, at any time, you harbour it, try the following amusing little experiment :
451.—A Simple Magneto Test.
Remove cable from magneto contact terminal. Take a flash-light bulb—one of the " toy " variety, which ordinarily ranks as a bit over 3 volts. Set plump on the magneto contact post (whence you removed the cable), the contact on the bottom of the bulb, and while so holding it bridge over with a screwdriver blade from the side of the bulb metal to the transmission cover. (See sketch). Then get some kind friend, who needs a little exercise, to go to the starting-handle, and to turn as if he was trying to start the car. (Of course, he cannot do so, beca.use you have disconnected the magneto from the coil). Now watch what happens to the flash-lamp bulb. If it
lights up brightly, you know that you are getting at least 3 volts, and that is useful information. (Of course, it will not continue to glow brightly, but will only shine out when your kind friend is actually turning hard). Do not keep the light going, not only out of consideration for your pal at the crank, but mainly because the filament of the " toy " bulb will not go on passing much over 3 volts for any length of time.
If you can light a 3-volt,bulb really brightly in this way, there is not much the matter with the magneto. Indeed, I have found by actual experiment that, however good the condition of the magneto, it is difficult tc generate a current of much,more than 3 volts by turning the starting-handle when the weather is cold, and the engine is cold too. When things are warm, you can grind out a good deal more than 3 volts, because you can then spin quickly. In my experiment, I took bulbs of different voltage, and worked in the dark, so that I could judge well of the brightness of the light produced. I found that a
824 4-5-volt bulb lighted up poorly, and that a 3-4-volt bulb lighted up well, From this, I infer that, in hand-starting, you expect the Ford engine to "catch on" with a voltage of less than 4 from the magneto, when everything is really , cold. That is asking a good deal of it, and explains the difficulty of starting the Ford engine in such circumstances.
It must, however, be remembered that a good deal depends on the heftiness of the man at the starting. handle, and upon his handiness at the job. One who knows how to "swing" the engine with continuous turning will certainly produce a good deal more than 3 volts. And, for the same reason, the starting motor will give much more than 3 volts, and will for that reason set the engine firing when a series of jerks on the starting-handle will do no good.
The point that I want to make is that there is nothing mud] the matter with your magneto if, in such an experiment as that described, you can get a 3-4-volt bulb to flash really well.
Here some well-informed driver will raise the natural question : "But why did not you think to test the magneto output with a voltmeter, connected up in the way in which the bulb was connected up 'I" Because the ordinary voltmeter is not an accurate indicator when it becomes a, question of measuring alternating current, such as that produced by the Ford magneto. The ordinary voltmeter is built for the measurement of direct currents (such as that given by a battery). A lighting bulb will serve—in a rough-and-ready way--to indicate the voltage of either direct or alternating current, its brightness telling the tale. And I had not by me an alternating current voltmeter : indeed, such voltmeters are not in everybody's hands, being used only for special tests,
452.—A Little Bit of Electrical Fact.
Do you know that, in a low-tension circuit, you get a spark only at a break—not at a make? Suppose, for instance, you take a _wire from your battery positive terminal . (the negative terminal remaining " earthed" as standard), and touch the free end of that wire against some part of the frame, then removing it, you will find that you do not get a spark at the touch, but only at the " go." On the other hand, whenever there is either a make or a break in the high-tension circuit, you get a spark at the plug—one at the make and one at the break.
I am not going fully into the subject, but I thought you might be interested in this fact, which is not known to everybody.
The low-tension spark is something quite different from the high-tension spark. When the low-tension spark happens, you get an actual transfer of fine particles of metal across the gap. (It is partly this that makes your coil points "ragged" or pitted in course of time). When the high-tension spark happens the transference is much less marked because the current is always rapidly changing direction and it has also less actual "burning" effect on the metal of the plug points.
Of course, when your tremblers buzz, you get, at each coil, and at each buzz, quite a number of makes and breaks, i.e., at the rate of 100 per second, and every time there is a break there is a spark there ; while, every time there is either a make or a break at the coil, there is a spark at the plug points.
A spark in a high-tension circuit represents the completion of the circuit in the gap : a spark in a lowtension circuit represents only the dragging away of the metal from the contact points, and the incandescence of the metal dragged away.