WORKSHOP AND GARAGE NOTES.
Page 69
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Useful Contributions from Our Driver and Mechanic Readers.
A Turning and Boring Tip. TT is often necessary for a driver1 mechanic to cope with jobs of turning and boring where no micrometers are available, and often with a somewhat limited knowledge of lathe work, as one can hardly expect a man who has had to learn all about motors to be a thoroughly expert turner, although he may be quite able to do an occasional job.
" T.F.E.," of Keighley, recognizes this and offers the following instructions. In many cases it is not possible to offer a shaft up to a hole that is being bored out in a lathe, to see whether it be an accurate fit, or it may be necessary to turn a shaft or bush to fit a hole into which it cannot be tried. In either of these cases be has to trust to measuring with callipers, which is by no means an easy operation, and requires all the skill of an experienced turner, so any tip that will make the job more certain should be welcomed, as if too much metal be removed the job will have to be sera pped.
In the case of measuring a shaft preparatory to boring a hole to fit, it is as well to know how to use callipers. They should be set so that when lowered over the shaft, of their own weight, one can just feel the slightest reEiNtance as the ends pass over the centre of the shaft. No accurate measurement can be taken if We callipers be forced over the shaft, as most callipers will spring to the extent of several thousandths of an inch, which is often quite enough_to spoil the job.
Having set the callipers accurately to the size of the shaft, a gauge can be made by taking any piece of wire of, in. diameter, and forming the ends as shown; this gauge should be made to fit the callipers in exactly the same manner as they fitted the shaft. If by any chance, in making the gauge. too much should have been filed off so that it is a loose fit in the callipers, it can be slightly stretched by a few hammer blows. Having made the gauge to the callipers, we now come to boring the bole. If this be bored to exactly the dimensions of the gauge, it will be found that the hole will be too small to allow the shaft to enter, so a certain amount of clearance must be allowed, and without a micrometer this Is not easy.
"'1'.F.E." suggests that this can be done by rocking the point of the gauge, as shown, when it is upright in the hole. It is best to hold the top part of the gauge against the upper wall of the hole, and to rock the lower point from side to side until a central position can be found, advancing the lower point all the time until a perpendicular
position is obtained. When at this point a certain amount of rock should be felt, and the formula of is that for 1 ft. diameter of hole there should be a rock of j in. for a driving fit and in. for a working fit. All other diameters should be dealt with in the same proportion, as, for instance, 24 ins, diameter should have 1 in. rock for a working fit and in. for a driving
fit; 3 ins. diameter should have in. rock for a working fit and 3/32 in. for • a driving fit.
Valves Sticking in Their Guides.
THIS may happen through poor lubri cation, and it troubled " T.W.," of Heckmondwike, until he tried the following plan :—He obtained a piece of felt about in. thick and made some washers to fit on the valve guides, leaving them about in. from the _bottom of the guide. Each washer was then saturated with thin oil, and he tells us that the valves will now run for days without sticking.
A Temporary Distributor Spring. A RARE trouble, but one that is liable to occur and when it does happen may cause considerable inconvenience, is the subject of a contribution sent to us by "D.D.I.," of Cleckheaton. This fault is the breaking of the spring or springs which hold the distributor case to the body of the magneto. It is, of course, possible to tie on the distributor by means of string, but this is apt to work loose, and a better method of securing the case is to use a fairly strong elastic band, such as one cut from an old inner tube or a garter.
Only the garter is mentioned by "D.D.I.," but we suggest the alternative, because we are not certain that the other article mentioned would always be available—at least, easily or conveniently.
How to Test Oil.
im is only on rare occasions, states
" DAlacG.," of South Uist, that drivers have to test oils in any way, except, of course, by comparing .the results obtained by the use of various brands of oil in the sump.
However, it may happen that one has " to test some oil to see if it be, say, dirty, and it will then be as well to know how to proceed.
A good method of detecting dirt in oil is to allow a drop of the suspected oil to fall on a sheet of blotting paper and then a drop of clean, unused oil beside it. If the paper then be held before a bright light the presence of dirt in the oil can easily be seen.
When one is comparing the quality of two different brands of oil, a good plan is to place a drop of each kind on a sheet of tin and to evaporate the oil by heat. The presence of dirt or carbon can then be seen in the sediment left on the sheet of tin.
Rescuing a Sparking Plug from a Cylinder.
WHILE cleaning his sparking plug a
correspondent, " A.R.," of Swindon, had the misfortune to drop the internal part into his cylinder. He tried several means, such as the use of pliers, loops of wire, etc., but none of them would enable him to remove the pItte centre, although nearly doing so several times. At last he hit upon the idea of putting a handful of tangled string into the cylinder, and cranking the engine round several times, after which he removed the string and found the plug centre entangled in it. This idea saved him the trouble of taking off the removable head of the cylinders.