IDEAS ABOUT IGNITION.
Page 31
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Some Instructive Advice from Our Driver and Mechanic Readers.
MHE FAILURES which occur in con
nection with the modern magneto are few indeed. Generally, when ignition trouble does occur, the driver with any experience worthy of the name is able to locate it at once, and, normally, can put the matter right in a very few minutes. One such trouble—with which the majority of drivers are more or less familiar—occurs in connection with the fibre insulating bush in which the pivot of the contact-breaker rocker arm takes a bearing. If this bush is allowed to get wet it swells, thus shrinking the hole and tightening the bush on its pivot. The only remedy is to take down both contact-breaker arm and bush, cleaning the pivot of the former and the hole in the latter.
This occurrence is so common, comparatively speaking, that we should hardly have expected, at this late date, to come across any new method of dealing with it. Yet, as a matter of fact, we have two letters this week, both of which embody suggestions for dealing with the trouble in question, and both have the welcome characteristic of novelty.
One a them is from a, foreman (" W.H.B,," of Charlton), who informs us that he is responsible for the care of 52 lorries. Obviously, then, he is a man whose opinions must carry considerable weight and whose advice must be well worth following. It is easy, he says, to take down the contact breaker, and it is equally easy to clean the pivot pin, using a piece of very fine emery cloth for the purpose. It, is not so easy to smooth out the interior of the hole in the bush, and it is most essential that this hole be eased out, otherwise an early repetition of the occurrence is likely He has discovered that the long centre screw, which helps to hold the stationary part of the make-and-break block in place, serves admirably as a reamer for this particular job, as it is eactly the same size as the pivot pin. The method of use, as recommended by this correspondent, is rather ingenious. First screw this centre pin into the bush, and then • draw it out, push it hack again, and draw out once more, repeating this process until it moves quite freely. By that time the hole will be sufficiently and properly enlarged, and the contact breaker may be reassembled in its place once more.
A letter from "WITS.," of Middlesbrough, deals with the same subject. This correspondent has had trouble develop in another direction. As the result of the swelling of the bush, the
boss in which. it is held has split. Instead of scrapping the base on which the boss was formed, he machined the split boss right off by means of a pin drill, specially made for the purpose. Having done so, he drilled and tapped a 16g-in. hole, screwed fine thread, subsequently making a new boss with a 165,in. shank
to fit into this hole. The interior bore of the boss was finished smooth, so that, in the event of the fibre bush seizing on its pivot pin, the bush would then revolve in the boss. This, he informs us, is quite satisfactory; indeed, in his opinion, it is more so than is the standard equipment, as the outside of the bush, being much larger in proportion than that of the pivot pin, presents a. larger surface for wear, and in consequence lasts much longer.
This same correspondent also refers to another difficulty which he has experienced in connection with Bosch ma.gnetos. In these machines there is, in his opinion, not sufficient room for the proper movement of the bell-crank lever, so that thee insulated block which it carries sometimes fouls the boss for the carbon brush, causing a short to occur between the rocker arm and the insulated block. This he has frequently found to be the originating cause of mysterious spitting and back-firing into the carburetter. To prevent its occurrence, he makes. a point of filing the bottom of the insulated block on the contact breaker, to increase the clearance. Further to that end, he also removes the pad on the boss on the carbon brush. Since adopting this procedure he has had no trouble whatever.
Sparking-plug troubles, more or less severe in their nature, we shall always have with us, partly because it seems to be the ease that all sparking plugs are not equally suitable for use in any particular engine, the selection being narrowed by an engine's predilection to oil up, or heat up, or behave in some other special manner so as to effect the efficiency of its sparking plugs. "
of Rotherham, has apparently had to deal, at one time, with an engine which was liable to over oil, and in connection with which, he found, the single-point plugs with which he was " issued out" were not, to put it, mildly no good as they might have been. Eventually, after much trouble due to this•eause, he decided to see what he could do in the way of converting these single-point plugs into multi-point ones. Ile removed the central electrode and placed,dt in the lathe chuck, sparking point outwards. Taking a suitable file, he turned down this end to a diameter of 3-32 in. for in. of its length, leaving a square shoulder where the diameter
increased. Taking a castesteel :collar, he shaped it to size and form shown in the sketch, giving it practically a. razoredge, and drilling it so that it was a running fit. on the turned-down end of the electrode. He reassembled the plug, and fitted the washer on the end of the electrode, which was then riveted over so that it prevented the washer from dropping off, but did not interfere with its capacity to revolve freely on its spindle.
In use the affect of the vibration and the explosions within the cylinder was
such as to'cause the washer toarevolve, with the result that a fresh portion of the circumference was continuously being presented to the other sparking point of the plug. Carbon, therefore, never got .a chance kto form a bridge between the two electrodes, and perfect eplug performance resulted. In actual fact, the first run which. the lorry did after the plugs were altered was 500 miles, which distance was covered in under 30 hours. No ignition trouble whatever was experienced on the trip, and, on examination, the washer was found to be perfectly clean and to have retained its original quality of hardness. It has given no trouble since.