FORD VAN POINTERS.
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By R. T. Nicholson (Author of "The Book of the Ford ").
OF COURSE, YOU know all about the electricity on the Ford : because, frankly, I do not! There was once a student of electricity— whom we will call Smith—who went up for examination in the subject. Ile did not know too much about it, and floundered a, good deal in his answers to the examiners' questions. At last, one of the examiners got a bit tired of it, and said : "Well, Mr. Smith, you don't seem to know much of the details of the subject, but perhaps you can at all events tell us what electricity is ?" Smith stammered for a while, and then said : " I—I—I—did know, but I've clean forgotten!" Whereupon the examiner turned to the other examiners at the table, and said : "Here is a terrible catastrophe, gentlemen ! We have before -us the one and only man who has ever known what electricity is—and he has clean forgotten."
21:—Understanding Electricity.
So I do not pretend to know all about electricity, even the simple sort on the Ford. All that anybody knows is that electricity is a form of energy which, under certain conditions, behaves in certain ways. All that I want to do here is to give you a simple working notion of the way in which the Ford electrical devices behave, when the conditions are right, and how you can set those conditions right, so as to make the system behave properly, which is, of course, how you want it to behave. I do not mean to go deeply into the subject, but simply to give you the rock'bottom facts, by thinking round which for yourself, you may be able to get over your road troubles, so far as they depend upon the failure of your electricity.
You know that the magneto is the generator of the electricity. That is out of sight under the transmission cover, attached to the flywheel of the engine. Do not let us worry over the question how the magneto manufactures the current : let vs take it for granted that it does. From the magneto contact a cable rises to a binding post on the back of the coil box : that is the first main part of the circuit. From that, the path lies through one of the four coil units in the box (assuming that the switch is on). From that, the loath is by one of the four thin covered wires that run from-the coil box to the contact-breaker—or commutator, as it isLsometimes (wrongly) called. There the electricity runs to earth (" earths," as it is wrongly described), and using the engine, or other metal, completes its circuit back to the magneto That is what is known as the low-tension circuit. Electri4ity will only work when there is a complete circuit for it—out and home, so to speak. If you cut or interrupt, the path at any point, the electricity goes off work.
This circuit is called the low-tension circuit, Le. cause the "sting "—the vim—of the electricity in ii is of a comparatively mild order, being more persis A42 tent than vicious. If you get a, shock from it, it is only a mild shock ; for instance, the kind of shock you may get when fiddling with the tremblers at the top of the coils.
So far, I have said nothing about the sparking plugs and their cables. They belong to the hightension system. What you see are four cables that run from the back of the coil boxes to four plugs. How exactly are those cables and plugs related to the magneto current?
They are related but not connected at all. The idea of most people) is that the current goes from the magneto to the coil, and comes out by the sparking plug cables to the plugs themselves,' there sparking. But that is all wrong. We have already traced the path of the magneto'current "out and home," and have seen that the sparking plug cables, and the plugs themselves, are not on that path at all. The truth is that there are two paths. One we have traced : the other we will now map out. Not only is there no connection between the two paths (except a very slight one, as we shall presently see), but it, is essential for the proper action of the coils that the two paths shall be well insulated from one another.
Inside each coil unit there are two coils of wire. (It is because of those coils that a coil is called a coil.) By a coil of wire, I mean a spiral, more or less like a long spiral spring. There is one open coil of a short length of wire through which the low-tension current passes. Beside it is a close, tight spiral, consisting of a great length of wire, insulated from the other by a thick coating of paraffin wax. Connected with the second spiral, a cable runs from the coil unit to the sparking plug, conveying the "cur'rent." Inside the plug, the path is broken, at the plug "points," by a, gap. If this gap were wide enough, the path, or circuit, would be interrupted to such an extent that there would be no electricity at all in it : but the gap being only a very little one11-32nd of an inch being about right—the current jumps the gap as a spark, running to earth on the other side, and travelling back by the metal of the engine, and one of the four low-tension wires—the thin "commutator" wires to the coil.
But as there is no connection between. the two wire
coils in each coil box, how could ,the electricity in this second—high-tension—circuit start?
It starts by what is scientifically called 'induction. There is nq connection between the ,twc spirals, or coils, at the start. The current in the high-tension circuits startsiin the coil by a kind of electrical sym pathy. It is something like wireless telegraphy. Though there is no path from the low-tension coil to the high-tension coil, the current arises iii the latter because there is some mysterious law which starts a current in a second coil standing close to, but insulated from, a first. Why not use the low-tension current for the spark at the plugs? Because it would not be vicious enough to fire the mixture.
What gives the high-tension character to the second circuit? Na one can tell you exactly what it ; but it has something to do with the number of turns in the high-tension wire spiral, as compared with the number of turns in the other low-tension wire spiral. The greater the number of turns in the high-tension spiral as compared with the number of turns in the low-tension spiral, the higher the tension the greater the spitefulness—of the second circuit. . Do not run away with the idea that the coil box in this way creates a great deal of electricity out of a very little: that would mean that perpetual motion would be possible. What the coil unit does probably is, so to speak, to save up the low-tension current for a comparatively long time, and then "spit it out" very suddenly; in concentrated form, for a fraction of an instant. If I were speaking in scientific terms, I should say that the voltage of the high-tension current was enormous, and its amperage low • while, on the other hand, the amperage of the low-tension current is considerable, and its voltage poor. Or you might regard it as a question of leverage. You know that an ounce vill move a ton, given. sufficient leverage. The lever does not create energy ; it simply applies it. That is what the high-tension coil does with the energy "induced" by the low-tension coil.
All of which accounts for the fact that when you get in the way of the high-tension current, for instance, by touching a. sparking plug top, or some bare metal forming part of the high-tension circuit, you know it! The low-tension current only reminds you that it is there : the high-tension current tells_ you to "get out!" I have said that the two coils (the low-tension and the high-tension) in each unit are insulated from one another, and that they have to be. That is not strictly true : there is a little bridge of wire from the low-tension to the high-tension spiral, or coil, placed there so that when the high-tension current retUrns, via one of the low-tension coils, there may be a path back for it to the high-tension spiral where it started. Remember, the circuit must always be complete, or no electricity! That little bridge of wire has, however, nothing to do with the transformation of the low-tension electricity into high-tension electricity. In the old days, coils were made without this bridge, the return being by a separate path of wire. The bridge is only used because it is convenient to use the "commutator" wires for the return, and because they go to the low-tension spiral, and because there must be a " through " connection for the high-tension system. I have said nothing as to which coil unit, and which low-tension wire, or which plug cable, or which ping, is working at any particular time. That is decided by the contact breaker, or "commutator." In the cover of that contact breaker are four metal contact pieces. Pressed against each of those contact pieces in turn (by the action of the engine) is a roller, which turns with the engine. The current therefore flows through each coil unit, through each low-tension wire, through each plug cable, through each plug, in turn, and thus keeps the four cylinders firing in their proper order. I have spoken of the electricity flowing as a current. Honestly, I do not know whether there is any flowing of a current—any movement of energy along the paths provided. But something happens in those paths, and it is convenient to speak of that something as a flow, 3ust as we should do if it were a case of water in a pipe. It is probably better to conceive ef electricity as feeling. As you know, you feel with the helpof your nerves, which correspond with the wires of an electric circuit. Cut a nerve right through, and there is no feeling. Yet, so far as we know, the nerve carries no "current," there is no movement along it. More than likely, there is no movement along an electric wire. Yet, cut the wire, or interrupt the current, and there is no electricity.
I have said nothing in the foregoing about certain details of the electrical equipment, e.g., the trembler on the top of each coil unit. These tremblers are in the low-tension circuit. They are there simply as a means of providing a succession of high-tension sparks, instead of a single one, and thus making the ignition more certain. If only a single spark' were wanted, it would not be necessary to have the tremblers, or vibrators, at all. "Plain" coils—that ;s, coils without tremblers—were at one time quite common on motors.
I have gone pretty deeply into this matter because the driver who really grasps the rock-bottom electrical facts that I have set forth will be better able than* the "rule-of-thumb" man to deal with any.
troubles that he may meet. He has simply to remember that there are two paths, or circuits, thateach must be complete, that there must be no short cut in either circuit by which the current may " sneak " home (or leak hoinR) till it is past the busipess-points : and the business points are :— (a) In the low-tension circuit, the "corninutor ' roller, where the current "earths." (b) In the high-tension circuit, the "other eide ' of the sparking plug gap, where the current "earths."
Electricity will always take a short cut home—or short-circuit—if it can. That is why we provide insulation at, all points where we do not want it, to have a chance of "shorting." We let it "short' once it has done its job. " Earthing " is only shorting.
Though the current on the Ford never really runs to earth—the ground proper. "Earthing" means merely getting home by any metal part of the engine or chassis.
22.—Fixing the Exhaust Pipe.
At the front end of the long exhaust pipe there is a big nut, whicb connects up the pipe with the exhaust manifold, and thus with the engine itself. Jt has a way of working loose in some cases, and once it gets into that habiOit is very difficult to make it "stay put." Its slackening is at first indicated by a "squiffy" hiss under the footboards, which has gradually become more and more pronounced, as the nut further loosens, until it becomes a pop, and eventually a bang.
Mere tightening of the nut is useless : it will only get loose again. (By the way, the nut calls for a big spanner—a ,bigger one than, is found intthe regular kit.) The thing to do is to slacken the nut right backoff the thread on the exhaust manifold ; then to dean the thread with.paraffin ;then tohvipe it dry, and paint it with seccotine, ,gold-sizerur' boiled oil ; then to replace the nuts as tightly as possible. The effect of this treatment is that, when the engine next gets hot, the seecotine, gold-size, or boiled oml. will be burnt, but will leave a residue, which will choke the threads, and so prevent the • nut from turning hack "on its own," though it will not prevent removal of the nut, when required.