SPARKING PLUG TESTERS.
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Simple and Effective Devices Constructed by Our Driver and Mechanic Readers.
WE ARE awarding the 15s. prize this week to " of Iligngate, for his ingenious design of a tester for a sparking ping. He is of opinion that the 'majority of such teeters on the market tire defective. His own, which can be made by anyone who can sharpen a lead pencil, is certainly cheap, hut even its designer has to admit that it has certain defects, as, for instance, in some of its uses, the spark produced is so weak that it would not he visible in strong sunlight. Incidentally, he tells us that he has taken out a provisional patent for this design, but has not completed his -application.
The design and construction of this teeter is almost sufficiently apparent from the accompanying sketches. It is made, as may be seen, from two pieces of kad pencil, and a point protector, thelatter being of the type which usually incorporates a small piece of indiarubber. The indiarubber is to be removed, so that its place may be taken by the short piece of pencil, the entering end of which must, be bevelled off at an angle cif approximately 45 degrees, as shown. When in place, this piece of pencil should be firmly secured, so that it will, neither pull out nor revolve. The other and longer piece of pencil must be doubly chamfered and pushed into the protector from the other end, being left comparatively free both to revolve and to more endwise. The reason for this is that by twisting it with the doubly chamfered end touching the tip of the other pencil a cam-like action occurs, and the gap between the two carbon cores can be adjusted from nil to a maximum of about one-eighth of an inch. Creater ''amps than this can, of course, be obtained by moving the longer pieos of pencil out of contact with the other. • • The method of using these plug testers is well known; " HUI.", points out that the theory is approximately as follows ;— A "sooty" plug is one in which the gap between the points is bridged by carbon. As this is a.good conductor of electricity, the current, passes that way and to the cylinders back to earth rather than across the gap, in the testes'. To testsfor " sooty ' .plug therefore reduce the gap in the testes to a minimum, non passage of a spark is a pretty sure indication that soot is present.. To test if the plug is oily use a larger gap in the tester. TIM spark will still jump. because there is less
resistance in a a-in. gap in the open air than there is through oil under compression. The same effect is to be seen if the plug' points are: too far apart. " M.EI,W,," of Newport, Isle of Wight, makes a simple combined spark gap and plug teeter from short pieces of brass and fibre. A piece of the latter
should be cut 21 ins, long, wide, and i-in. thick. Orin three 2ho1es, one near each end, and one in the centre. That at one end and the one in the centre should be elongated to form slots, as shown in the sketch. Their actual length and the reason for making them will be apparent later. A piece of brass is required the same size as the fibre. It should be tapered to a point at one end and have 'three holes' drilled in it,. as in the ease of the fibre, except that none Of these needs to, be elongated. Bolt the brass and fibre together as shown in the sketch. One hole in the fibre, the one which was not made into a slot, •acCommodeles the sparking plug terminal. The Opposite. end hole hi the brass is con.
fleeted up to the end of the high-tension wire. It 19, now possible,-by means of the slots in the fibre, to adjust the length of the !park gap,which is actually thedistance between the tapered "end of the brass and the nut on the sparking plug terminal.
" If sparking is •occurring regularly," says this contributor, "at the gap, while misfiling is taking place in the engine, ni sure-indication that the magneto is in order and the sparking plug at faults or, if on-exatninatiOn the sparking Plugs are proved to he in order, . then the
trouble may probably he traced either to the valve or the mixture."
. The plug tester which is suggested by " C.S.,' of Preston, is.simplicity itself. Take, he says, a strip of wood 2 ins, long and in. square, and psi through it a piece of stiff *ire 6 ins. or B ins.. long. Make a hook on one end of the wire for attachment to the plug terminal and gauge the strength of the spark or the condition of the ignition apparatus by causing the free end of the wire to ap, preach closely to the metal on the cylinder. " of Anglesey, tells us how te do withont a spark plug tester. As a rule, he. says, a screwdriver with a wooden handle is recommended as being a valuable, if not essential, tool for use when testing the strength of the spark at any plug. Unfortunately, the majority of tool equipments nowadays do not include a screwdriver with a wooden handle. It is usually an all-metal one, and, therefore,not quite so suitable for thepurpose as the older type. It may not be generally known, however, that. there is no need to go to the espense of a wooden-handled screwdriver or of any other special gadget for, making these tests. Any long piece of Metal such as a metal screwdriver, a, spanner, or titre lever will serve the purpose.
When about to test a plug, place one end of this tool on the cylinder as, for example, at the point indicated at A on the sketch, and hold it en that it passes over, but does not touch, the terminal of the plug which it is desired to test. Then, keeping the point of the tool still on the metal of the cylinder, gently lower until almost. touching the plugs, watching for the spark, if any, between the plug terminal and the tool. The distance from A to B being shorter than that from B through the arm and-body of the -operator, there will be no tendency for him to receive a shock. It is important to remember, when releasing the tool, to lift it well away from the plug before taking it off the cylinder, otherwise a shock will pass to the operator. The rule is to apply : first on A then on B; to releaee first off 13 then off A.