SOME WORKSHOP TIPS.
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A Lapping Tool. Aids to Testing. Notes on Brazing.
THE LAPPING•OUT of a cylinder, in order to make it fit to take an oversize piston, is work of a strenuous mder, especially when it has to be done by hand. So at least states "A.M.D.," of Lanark, to whom we award the 15s. prize this week, and we imagine that few readers of this page will be inclined to argue the point with him ; few, . at any rate, amongst those who have had any experience of the work. It is particu. tarty arduous, he goes on to point out, when the lapping tool is Merely an old piston, which, when it is passing that part of the bore of the cylinder which is least in diameter, requires a good deal of pushing and pulling. He sends us a sketch, which is reproduced herewith, of a suitable tool for lapping cylinders, by the use of which much of the labour is eliminated, or, at least, rendered less arduous.
The tool, as sketched, is designed for use on a Ford cylinder block. It is inade of an old piaton, sawn in two, the saw cut being sufficiently wide to reduce the effective diameter, of the piston to the extent needed to afford the essential clearance between it and the cylinder walls. The gudgeon-pin bushes have been removed, one of them entirely, the other being cut in halves transversely, and the halves replaced, as shown, to afford resting places for the ends of the two coil springs ehewn in the sketch.
Further description is unnecessary. The springs maintain a fairly even pressure between piston and cylinder walls, but give sufficiently, in the smallest part of the bore, to reduce the intensity of the effort required.
CERTAIN useful suggestions in con-Juection with road testing of repaired chassis are made by "11.N.T., ' of Lewisham. The most helpful concerns the arrangement of fuel tanks for facilitating the oorrect measurement of fuel consumption. TWO tanks are required. One, the smaller, should be about 3 ins,
diameter and 18 ins. long. The base should be conical, as shown in the sketch, with tap and connecting pipe to the float chamber of the carburetter. Quite near the bottom of the tank, say about k in. above the junction between the conical and cylindrical portions, a hole must be drilled, to receive a glass tube, which is bent at right angles, near its lower end, for the purpose, and which must, be long enough to reach to the top of the tank, when the lower end is inserted in the hole mentioned. The tube may be secured in place by a cement compound of acetone and celluloid, the mixture being such that, when applied, it is a little thicker than glue. This makes an excellent petrol-proof joint. The glass tube must be made to lie close In the tank, which is clipped to the dashboard, and can then be graduated in tenths and twentieths of a pint.
The upper end of this tank is closed. and connection .nade between it and a larger one, preferably about 6 irks, diameter and 2 ft. long, which is made and equipped in the same way as the smatter tank, with glass tube, conical base, and so on, except that it is graduated in half pints only. The outlet connection from this tank is coupled to the inlet of the
smaller one The top ie closed, but equipped with a convenient filler cap, with air vent, as usual. The larger tank may more conveniently he mounted in the driver's cab, provided that its position is such that there is a reasonable
fall from it to the other tank.
The object of providing two tanks is to allow of finer readings being taken,. such as are only possible with a tank of small diameter, whilst providing sufficient fuel capacity to allow of a reasonably long test run being undertaken. Petrol can be supplied from the larger tank to the small one in pints or half pints as -required, and the run may be continued without stoppages for replenishment.
BRAZINO, according to " A.R." of
Manchester, is still preferable to welding for a good many operations, and he deprecates what he declares to be the present tendency, to turn to the oxyacetylene blowpipe whenever a junction or a repair has to be effected, In many cases, he points out, the high temperature at which welding is carried on may have the effect of seriously distorting the parts adjacent to those which are being subjected to the operation. Brazing is almost invariably to be preferred, in his 'opinion, in the case of articles made of brass, bronze and malleable, iron. The last-named metal, in particular, is liable to lose its especial characteristic of malleability if subjected to excessive heat. In all these metals it is possible to execute a brazed joint which will be at least, as strong as the metal itself, and the repair will in no sense be second to a 'weld, provided always that the work is well and properly carried out,
The most effective means towards the execution of a good brazing job is cleanli
mess of the parts to be brazed. Iron parts must be cleaned by filing, scraping, chiselling or grinding, whilst brass, copper, or browse pieces are best pre pared
pared by dipping n a fluid containing one part nitric acid and two parts sul. plinric acid. Both these acids are poisonous, and must be handled with great care.
The best flux for brazing is borax, finely powdered.
When brazing cast-iron, difficulty is sometimes encountered because of the presence of free carbon or graPhite in the iron. The preliminary cleaning process, therefore, in the case of this metal, requirts to to be slightly different from that outlined above, The metal must be raised to a dull red heat, and the surface thoroughly scrubbed with a wire brush. When ready for work, clamp the parts together in the positions which it is desired they should occupy when bras. ing is completed. Care should be taken that the clamping doe a not impede access to the joint, and that it does not prevent the parts being turned round whilst they are in the course of being brazed.
• When ready, put the work on to a good solid coke fire, and bring the heat up slowly to a bright yellow. This may he done with every confidence; there is no fear that the metal will be burned in the process. Spelt-sr may then be applied, the quantity depending on the circumstances, and being influenced to a greater extent than most people would believe, by the cleanliness of the parts.
A good flux for use when brazing castiron can be made of boric acid flea., pulverized chloride of potash 2 oz., and carbonate of iron 2 os. This mixture should he kept day, as moisture reduces its efficacy. Mix this flux with brazing spelter immediately before commencing operations. After brazing, allow the parts to cool slowly.