FORD VAN POINTERS.
Page 26
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By R. T. Nicholson (Author of "The Book of the Ford ").
IN MY LAST Ford Van Pointers I was dealing. with erratic firing, the causes of it, and the different methods for dealing with it. I pointed out that prompt attention should be given to this matter, because erratic running of the engine is unquestionably had for the transmission.
534 (contd.).—How to Tackle Ignition Troubles.
• We considered the advisability of assuming that when erratic firing occurs-that it is either aplug or a coil unit that is at the bottom of the trouble, and I described the tests for the plug and went on to say that in order to decide whether it is the coil unit or the plug that is at fault, the suspected unit should be exchanged for some other in the coil. box, and if by this method the coil unit is discovered to be faulty, a spare unit should be substituted.
If you have no such spare, you must dicker with your unit, though this is vexatious work on the road, when you are anxious to get on. Ordinarily, you will be able to get on if you screw very slightly downwards the adjusting nut on top of the offending coil unit, but this is only a temporary makeshift. It may get you home, but the unit needs thorough attention at leisure. Generally, such attention means trimming the tungsten points on vibrator and vibrator bridge, though, if the contacts are too far gone, it may mean replacement of vibrator or bridge, or both. It is difficult for the amateur to trim these contacts really well. They should meet absolutely squarely, and should-be free from all pitting. The job is really one for an electrician. Do not try to hammer the contacts flat: harnmeringwill only loosen the tungsten from the steel which carries them. They must be filed trim.
Squaring Up the Coil-unit Contacts.
One pretty good way of making "all square" is this :—Pack the vibrator (the lower member) up from below, so that it is impossible to push it down. A shaved match will make a packing, and should be set directly below the contact. It should be of such thickness that it will just support the vibrator without lifting it from its usual resting position. Then slip a folded piece of emery-cloth between the contacts, with rough surfaces outside—against both contacts. Screw down the adjusting nut on top of the unit till you can only just comfortably pull the folded emery-eloth to and fro between the contacts. So pull it to and fro repeatedly till you have got the contacts square and free from pits. Every now and again tighten the adjusting nut slightly, so as to get more pressure to bear on the emery-cloth. Be careful to bend neither vibrator nor vibrator bridge. Blow dust away. Instead of a folded strip of emery-cloth, a very thin flat two-sided file may be used, or a sandpaper nailtrimmer, as used by manicurists (procurable of a hairdresser). These methods are tedious. Personally, I shirk the job, and get it done for me by somebody who can do it better than I can.
When the points are trim, they should be set by means of the adjustingescrew. When the vibrator is held down with a, finger as far as it will go, there should be a gap of a little less than 1-32nd in. between the contacts. You can adjust roughly by means of nut to this gap, and then, with the engine running on the other three units, adjust finally to get the best possible effect out of the explosion in the cylinder to which the unit belongs. Then lock the adjustment. Never bend either vibrator or vibrator bridge to get the gap.
If the contacts are too far gone to give further service (which will not be till they are worn or filed down to the base metal), replacement will be necessary. This is a matter of buying a new vibrator or bride, or both, complete, fitting and setting. This is a simple job.
Failure of High-tension Coil.
But there are cases in 'which this trimming and adjustment of the contacts will not set a coil working properly. The job that I have described takes care Fig. 359 —The spark gap test of the high-tension output of a coil unit, the end of the lead being held about a quarter inch from the terminal.
only of the low-tension element in the unit—sets the vibrator buzzing properly, that is. It is quite possible for the unit to buzz properly without giving a good high-tension stiark.
You can tell when this trouble is present by run
ning the engine with a gap of about set between the metal end of the sparking-plug cable and its binding post. (Take the terminal off when the engine is not running, for fear of gruesome shocks.) If you cannot get a spark to jump i in. the coil-unit has broken right down, and you must just get home as best you can—unless you have that spare unit aforesaid. N.B.—Hold the test cable by its insulation only, touching no metal, or—Ouk l—if the high-tension current conies.
The Editor draws my attention to a very simple device, which has been invented by an employee in the motor vehicle section of the Post Office, and which takes the place of the screwdriver in the testing of sparking plugs, recently referred to in these pages. I like the way in which the inventor (whose apparatus is described in the news pages of this issue) has carefully insulated the spring steel current deflector, and the waistcoat-pocket handiness of the contrivance.