FORD VAN POINTERS.
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By R. T. Nicholson (Author of "The Book of the Ford.").
IAM GOING to try to put on to paper all I know about sparking plugs, so far as concerns their• use on the Ford. 259.—Mica V. Porcelain Plugs.
Personally, I still swear by mica—as against porcelain—insulators. I do not say that there are no good porcelain plugs, but I do say that I have, on the average, got a lot more satisfaction out of mica plugs. This satisfaction has been due to one big fact : mica cannot break, whereas porcelain can and does.
Porcelain cracks, if it is hot and wet falls on it ; it cracks from a chance blow of a spanner or other tool; it cracks from the heat produced by the engine.
I do not say that, porcelain does this all the time and every time, but it does it sometimes, and mica never does it. I knovd one or two good makes of porcelain plugs that are ,all but as reliable as mica plugs, but I am speaking of porcelain plugs as a whole and mica plugs as a whole. . If you use porcelain plugs, take good care never to let wet get on to them when they are hot, and also never to knock them with a tool, whether they are hot or told.
260.—Cracked Plugs.
Never trust a cracked plug in an engine. It is not always possible to tell when a plug is cracked ; sometimes the crack is hidden under the metal body, sometimes under dirt on the porcelain (for it is only porcelain plugs that crack). So far as dirt is concerned, you can generally spot a crack (if any) if you first wipe the dirt away ; but I warn you that such cracks are often fine enough, to make very close inspection necessary. A microscope even will often come in useful. A cracked plug is almost sure to misfire; if the crack is very alight, the mis-firing will usually take place only when the engine is running a bit hot.
A crack hidden under the metal of the plug body may be a great source of annoyance, because misfiring due to it may be very difficult to trace. The mis-firing usually is not there all the time, but only when you are running the engine hot. You examine everything there is to look at, but still you find no flaw. Sometimes—when the break is a bad one— you can get at the bottom of the trouble by trying to twist the. porcelain round in the metal work with your fingers. Then, if broken, it may give suddenly. (Do not be afraid that you can actually break a sound porcelain in this way ; you cannot. If it gives suddenly, you will know that it was cracked before, and therefore useless.)
If you cannot detect the crack of a flawed porcelain in this way, the only comfort is that it will,
sooner or later, be pretty certain to show itself when next taken out. for examination. You will then find a broken-off. ring of porcelain resting on the .firing points. Once the ring gets. broken off—as it eventually does—the mis-firing becomes very marked, and is there all the time. You then have no trouble in " spotting" the cylinder in which the trouble lies; then you are very " warm " indeed,. and soon get " home" to the cause of the mis-firing. The hanging ring of porcelain tells you all about it. .
That hanging ring, by the way, may cause pre. ignition; that is, its edges may get so hot as to glow, and fire the mixture at the wrong point. If it any time your engine fires when the current is switched off, suspect a cracked plug. It need not necessarily be that, because anything glowing hot in a cylinder will cause pre-ignition ; but, in my experience, pre-ignition in the Ford engine is nearly always due to a cracked or broken pOrcelain. As a matter of fact, Ford. pre-ignition is very rare, but it can happen.
261.—Budging an Obstinate Plug.
But sometimes a plug will be obstinate even to your fixed spanner. Your fixed spanner is an open-ended spanner, and, therefore, is not quite as rigid as it should be. An " all-round " spanner is really best for the purpose, but the kit open-ended spanner is good enough in ninety-nine cases out of a hundred.
When you cannot budge a plug with that, a box-spanner with a hefty " tommy " will nearly always do the trick. That is, of course, an " all round" spanner, and the more you pull on it, the tighter it tries to grip, so that, short of splitting the metal of Which it is made, the plug has to budge.
Paraffin poured round the plugs in the wells in which they lie will help to loosen obstinate. plugs—particularly if the engine is warm, but not running, at the time. It creeps down the plug threads and so eases their grip. Give it a little time to find its way in. It. does not do to use the paraffin when the engine is very hot or actually running, because the paraffin then gets burnt up or dried up almost at once. On the other hand, comfortable warmth helps the paraffin to get down to work.
Fig.-0166.— A common fault—the broken ring of porcelain.
262.—Cleaning Plugs.
The best way to clean a plug is to soak it in paraffin (when cold) for a few hours, then to brush away all filth with an old tooth-brush, taking care not to upset the setting -of the sparking gap, and gently scraping away odd bits of dirt and, carbon that will not yield to the brush. After that, give it a petrol bath so as to dry out the paraffin. If you put your plugs back after a paraffin bath and without a final petrol bath, they will nearly always soot up and causeimis-firing at once.
qarie of the best plug-cleaners I know is one of those acetylene burner brushes not really intended for plug cleaning at all, They are to be bought— even to-day---for 6d. or so at a motor accessory. shop. They are something like a very small shaving brush with wire bristles. The briStles have a cover over them to prevent their getting bent when, not in use. You can push these wire bristles up into the body of the plug, and, by twisting them about, can remove the most obstinate carbon.
In cleaning the porcelains (if you have porcelain plugs), bo careful not to scrape the glaze off. If yondo, the.plug will soot up very readily when next brought into use. You cannot hurt mica in that way.
263.— One-point Plugs.
Buy one-point.plugs—that is to say, plugs with one long rod (or pole) right down the middle, and with one point only forming the sparking-gap between itself and that rod. Plugs are often made with two; three, or even four, gaps round the central rod. I do not believe in them. However many gaps you have, sparking will occur only at the smallest of thegaps at one place ; it will not dodge about 'all round the gaps. And if one gap gets sooted or oiled up, no spark will occur at the other gaps, simply because the current will cross by the bridge of oil or soot at the choked gap, and you will get no sparking anywhere. The more gaps you have, the greater are the chances of fouling up ; and, with any gap fouled .up, your sparking stops. So buy single-gap plugs. 611■11■411-.111111.
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Fig. 168.— The "one-point" and the "three-point" plugs.
264.—The Sparking Plug Gap.
One thirty-second inch, please. Personally. I believe in setting this gap by using a slip of metal 1-32 in. thickness. You can get such a slip at any garage; they will make one for 'you. The ordinary idea of setting the gap by means of a." thick visiting card " or a worn sixpence is altogether too rough and ready. The gap is important; and it is important that it should be the same at all the plugs.
One thirty-second of an inch is a big gap—a bigger gap than is set for most engines—but it is right for the Ford engine and ignition. A narrower gap, too, readily soots or oils up. Many, garage mechanics set to 1-40 in. ; and, while that is right for most ignition systems, it is too narrow for the Ford. In altering the gap, bend the central rod (or pole) towards or away from the projection that comes from the side, not vice versa. If you try to bend the projection towards the rod, it is about a hundred to one that you will break it off and spoil that plug. The projection is brittle ; it is made so by the heat to which it is exposed. It breaks like glass when the plug has been in use for any length of time if you try to bend it. Then, and only then, is there any advantage in having more than one gap ; because, with two or more projections, you. can set another gap. But if you make it 'a rule always to bend the central rod, you will not break things, fer that quite easily to side pressure.
265.—Preventing Plugs from Sticking.
If you brush the threads of your plugs with blacklead before you put them in, they will not stick when you next want to get them out. But do not trust to this alone when you are replacing an old plug. The threads of an old plug are nearly always jammed up with filth—mostly' burnt engine oil. Clear the threads by running a sharp pointed tool round them. It is the burnt oil that mainly causes plugs to stick. If previously soaked in paraffin, the filth can readily be removed.
266.—A Cable Attachment.
Some plugs sold to-day are furnished with a spring wire attachment which does away with the need of a thumb-nut. Fig. 170 shows what it looks like. As you pinch the " legs " of the spring grip together, you open the loop which embraces the threaded portion of the plug (on to which the thumb
n. u t generally goes). You put the cable terminal on to the threaded portion first. Then you spring open the wire grip by pinching the egs together, and slip the grip over the threaded portion' so that the loop lies hard down on the cable terminal. Then you release your pressure on the legs and the loop closes, gripping tight on the thread, and preventing the cable from .coming off.
You can easily make such a grip for yourself out of a, springy piece of wire, such as a safety-pin.