WAYS AND MEANS.
Page 69
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Some Useful Contributions from Our Driver and Mechanic Readers.
Determining Polarity.
TlIE following useful information is sent by "D.MacG.," of South Mgt :— Readers of this journal may often have found themselves in the position of having tyre wires connected to a dynamo or battery in their hands and being unable to decide which is positive and which negative. This short article is intended to enable them to cope with such a predicament.
A simple test is to place the two ends of the wires, bared of their insulation, on a piece of raw potato, a distance of a quarter of an inch separating the leads. In a short time the potato will turn green around the end of one lead. This indicates the positive (÷) lead. Instead of the potato, a strip of moistened blue-print paper may be used, in which case the paper around the positive lead will turn white. As a shortcircuit will result if the wires touch each other, a lamp may be connected in series with the positive lead, so that no damage will be caused by a shortcircuit.
A simpler and still more convenient test is as follows :—Obtain a tumbler of water and gently add a few drops of sulphuric acid to it. This is to make the water conduct the electric current. Pure water is not a conductor, but tap water containing mineral salts is slightly conductive. A teaspoonful of common salt dissolved in the water will serve instead of the sulphuric acid. Having prepared the tumbler of water, dip the two leads into it, tabing care to keep them from touching each other. Bubbles of gas will rise from the ends, more from one end than the other. This end is the negative (—) lead ; therefore the other is the positive.
Another equally simple test requires a solution of water and sodium sulphate (say 5 grains to the tumbler of water), to which is added a few drops of phenol phthalein. When the two lends are placed an inch apart in this solution the solution turns pink round the negative pole.
A portable tester can be made, using the above solution, from a piece of glass tubing S ins. by 1 in. Plug one end with a rubber cork and fill with solution. Then stopper the other end and place a piece of copper wire through each end. When two mains are connected to the wires the negative pole assumes a pink colour.
Driving in Fog.
EVERY lorry Man who has done much driving in fog or mist knows the difficulty of seeing when his acetylene headlamps are throwing large white cones ahead and possibly upward when his burners are set slightly below the centre of the reflector.
A method which "TM.," of Brighton, has used with success is as follows:— " Take a piece of heavy-gauge brass tube about 1 in. long, screw one end with a taper thrend to fit into the burner holder and tap out the other end with a taper gas tap to take the burner. Screw this into the burner holder and insert the burner in the top. This will have the effect of throwing nearly all the rays of light on to the ground just in front of the lorry.
For cone-seated burners a similar . adapter can be made as shown in one sketch from a piece of }-in, stick brass. For electric lamps with horizontal bulb holders make up an adapter with an elbow joint as illustrated. In the case of electric lamps with vertical bulb holders a straight adapter will do. The main idea is to get the source of light well above the centre of reflector.
Turning a Stiff Engine.
AFTER an overhaul it is necessary to
turn the crankshaft round while the bearings are stiff, so stiff, indeed, that the ordinary starting handle will not be found to give sufficient leverage.
" A.D.," of Londonderry, has suffered from this difficulty, so he has made for himself a device which, he tells us, he has found most useful. This consists of
a strip of mild steel, 2} ins, by in., which is bent round to fit the flywheel of the engine under repair. A piece of 11-in. by 4-in, iron is formed so as to make a lever, eyes are riveted to the hand and cross-pins fitted as shown in sketch.
The length of the band is so determined that it will form a gripping baud when the lever is moved in one direction, and will release its hold when moved in the reverse direction.
We should say that by the use of such a band the most obstinate of engines could be turned, and as it acts as a unidirectional device, it is only necessary to continue the backward and forward movement of the lever to produce rotation of the engine.
Preventing Float-chamber Leakage.
ONE of our readers, " D.D.I.," of Cleekheaton, noticed in a recent issue a description of a clip for holding down the cover of a float chamber to prevent it from chattering under the effect of vibration, and consequently causing flooding of the petrol.
He agrees that this tip was quite sound, but says that to put it into practice entails considerable time and material. He has used another method for some time and finds it quite satisfactory. He obtained an old inner tube from which be cut a band about 11 ins. wide, flattened it, and at one end cut a small slit 1 in. long and at the other a second slit in. long. The band was then put around the float chamber in the manner illustrated, the larger bole passing over the inlet connection at the foot of the float chamber, whilst the smaller slit fitted over the dome carrying the 'needle.
When it is desired to remove the cover it is a very simple matter to lift off the band, and it will remain attached to the carburetter so that there is no fear of losing it.
The bottom connecting nut for the petrol pipe was, of course, removed before the band was put into position.
Care should be taken to prevent petrol flooding over the rubber band.