FORD VAN POINTERS.
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By R. T. Nicholson (Author of "The Book of the Ford ";
IAM often asked whether I believe in fitting a hightension magneto system of ignition in substitution for the standard low-tension system. The almost universal use of the high-tension magneto system on engines other than the Ford has created the widespread impression that the high-tension system must be superior. Nevertheless, whenever I am asked whether it is a better system for the Ford, I say that, in my opinion, it is not.
490.—High or Low Tension Magneto ?
I take off my hat to the high-tension magneto. It is reliable, unfailing, unfaltering. But, for the Ford, I still believe that the Ford system is best. Here are ely reasons.
When the high-tension system is adopted it is gonerally because of the impression that it gives easy starting. It undoubtedly does give reasonably easy starting with most motors, but that is no guarantee that it will do so with the Ford.
. The fact is that such difficulty as there is in starting the Ford is due, not to the ignition system, but to the sluggishness of the .engine in turning over when the starting effort is made. There is no true neutral position of the engine on the Ford when the oil is cold. On most engines the gears are positively thrown out, thus securing a true neutral position. On the Ford it is the clutch that is thrown out ; and when the clutch plates are gummed up with cold oil, they will .not be thrown out; they stick to one another, so that when the engine is turned over the back wheels 'try to turn with it, and, as they are on the ground, and as the brake, too, is usually hard on, there 4is great resistance to the turning of the engine. Moreover, the brake and transmission bands also hold a lot of cold oil, so that they add further resistance by sticking to their drums. All of this gumming has to bewvercome before a spin can be. got on the engine.
All these obstructive conditions, moreover, are there as much when a high-tension magneto is in commission as when the standard Ford system is used ; and they work in precisely the same. way against the initial efficiency of both systems. If you cannot get a " live " spark with the Ford system, you will not get it with the h.-t. system.
A Comparison with the Ford Magneto System.
When the h.-t, magneto was first introduced there was quite a lot of objection to it on the score that it made for hard starting. Since that day improvements have overcome that objection. With the ordinary motor engine, starting is not difficult. But 042 it still remains a fact that., with the Ford engine" starting on h.-t. magneto spark is not easy. . It is, of course, true that if the .standard Ford i
system s in poor shape, substitution of a h.-t. magneto will work wonder's ; but, then, the converse 'would also be true—if you had a h.-t. magneto fitted. and it was not in good order, substitution of the Ford. system would work wonders.
Another objection to the use of a h.-t. magneto on the Ford lies in the fact that, with it, the sparking plug gaps must be reduced to 1-40 in., as against the standard 1L32 in. ordinarily set in Ford plugs. Now, the Ford engine is prone to over-oil—this being due to its system of lubrication. This over-oiling rarely matters if there is a good wide gap at the plugs ; but if the gap is reduced to 1-40 in. ignition failure is due, owing to the excess oil bridging the plug points. A further objection to the Use of a h.-t. Magneto on the Ford is to be found in the special fittings necessary. The fitting has to be carefully done, and .there is none too much room for them under the bonnet, especially now that the generator lies there. I.have known a good many cases of ignition trouble due to the unsatisfactory fitting of a h.-t. magneto to the Ford.
I agree that the h.-t. system does away with the trouble of " dickering " with the coil units. I also agree that, when properly fitted, it is much more reliable and fool-proof than the Ford system, but I do not agree that it makes for easier starting.
The Fundamental Difference.
There is really not so much difference'between the Ford system and the h.-t. magneto system. It is customary to speak of the Ford system as a lowtension system, but it is, of course, a high-tension system in final issue. The sparks at the plugs are h.-t. sparks. The main difference between the two is that in what is ordinarily known as the magneto both high and low tension systems are inbuilt, whereas, in the Ford, they are separated. This is a loose statement of the facts. I mean this. In the h.-t. magneto, both low and high tension coils lie round the armature, and there is no external l.-t. wiring. Only the h.-t. wiring appears externally. On the Ford system both low and high tension wiring is exposed to view, and the coils lie outside the magnet assembly..
There are, of course, also coils in close relation to the magnet assembly—the stator coils, from which the low-tension current is collected and delivered to the coils proper via the magneto terminal. It is the compactness, the very inaccessibility, of the h.-t. magneto that gives it such a vogue. Nothing can get at it to hurt it. There is no fouling with oil, no rubbing through of insulation. Furthermore —and most important of all—there are no tremblers on the h.-t. magneto to give trouble. The coil inbuilt in the h.-t. magneto is what is known as a " plain " coil, the efficiency of which depends on the sharp break of the contact points. This, of course, gives only one effective spark at each break (the second spark on the make being negligible), whereas, with the Ford trembler system, there is a stream of sparks across the plug points at each timed contact.
There seems to be no good reason in theory why the Ford coils should not be plain coils. Old style. motorcycles used often to be run on plain coils. Indeed, several systems of ignition intended to be used on the Ford are constructed round the map make-and-break plain coil principle, similar to that used in the 11.4. magneto. Among these are the Atwater-Kent and the Kelvin-Hardy.
Presumably, the reason why the plain coil system of ignition is not more largely used on Fords is to be found in the fact that the single spark produced at each break is less effective—particularly at the start—than the stream of sparks given, by the trembler system. It was for this. same reason that the trembler system was so largely used in the old days when batteries furnished the 1.-t. current. Plain coils were theh almost entirely abandoned in favour of trembler coils, notwithstanding the trouble involved in the trimming and setting of the trembler points. The Ford system is very Similar to the old batterytrembler coil system, the main difference lying in the substitution of a mechanicalfor a chemical generator. . In the modern Ford a battery is part of the standard equipment. This overcomes much of the difficulty formerly experienced in starting the Ford in cold weather ; for battery current is independent • of -engine speed. The only trouble that then remains is'that of carburation, which is apt to be sulky when the temperature is low. Moreover, if the engine resists you when you try to turn it over, you do not, of course, get proper mixture into your cylinders.
i That difficulty s, however, easily overcome by warming up the carburetter and induction pipe with hot water.
491.—A Simple Explanation of the Magneto.
In the accompanying diagram of the winding of a high-tension magneto, M represents the magnet ; C, • the core of the armature ; L.T. the low-tension wire, which continues round the core as the low-tension coil ; H.T., the high-tension wire, which continues round the core as the high-tension coil ; C.B., the contact breaker (" make-and-break) ; and RP., the pole pieces. Dotted lines represent high and lowtension " earth " circuits.
A magneto constructed exactly in accordance with this diagram would not, of course, work, for the armature would be unable to turn owing to the anchoring of the wire,s. Moreover, some important Working details are omitted for the sake of clearness. The diagram dees, however, illustrate main principles, and shows the correspondence between the high-tension magneto and the Ford magneto. In the Ford system the magnets rotate ; in the h.t. magneto the magnet (or magnets) Li Ordkiarily, stationary, although h.t magnetos have beer constructed with revolving magnets. In the Ford system the stator coil remains at rest, while in the h.t -magneto the coil turns. In either case the result is the same—the lines of force between and around the pole S are cut, and so produce the current. 'In the Ford system these lines of force are cut by the coil winding round the spools of the stator coils ; in the h.t. magneto system they are cut by the wiring round the armature core. The main difference between the two systems lies in the fact that, in the Ford method, the main coil (i.e., the coil on the dash) lies away from the magneto, whereas in the h.t. system the coil is inbuilt in the working armature. Note that in both systems the high and low-tension coils are bridged. The h.t. magneto has a snap contact-breaker, giving a spark each time the points are separated. The Ford system has a trembler on the coil which gives a rapid series of " makes " and "breaks" at each "wipe" of the timer. The timer corresponds with the distributor of the h.t. system.
492.—A Correspondent Testifies to the Value of Looking for One's Self.
That the h.-t. magneto can give starting trouble is clear from a letter which I have just received from a cm respondent. In his case, starting was not merely difficult, it was almost impossible. He had verified everything, as he thought, but took his h.-t. magneto for granted, more especially as the magneto
had been recently overhauled. Ile explains. But when I took off the cap on end of magneto I thought the segments appeared a trifle oily, also a trifle ridged, looking as they might do if heavily scratched with a pig. I used very fine emery cloth and smoothed and cleaned them. I did the same to the make-and-break points. I went for another grind at the starting handle, gave the handle three turns to prime the engine, then switched on, and—nearly had a fit, for it started at once, and has started like that ever since. When warm, it will even start with a two-finger pull."
Which shows. . . .1