Contributions from Drivers and Mechanics
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TEN SHILLINGS WEEKLY for the Best Communication Received, and One Penny a Line of ten words for any thing else published.
Drivers of commercial-motor vehic'es and tractors, and mechanics and foremen of garages or shops, are invited to send short contributions on any subject which is likely to prove of interest to our readers. Work. shop tips and smart repairs ; long and successful runs ; interesting photographs all are suitable subjects. Send a post-card, or a letter, or a sketch to us—no matter haw short, or how written, or how worded. We will "knock it into shape" and prepare sketches, where necessary, before publication. The absence of a sketch dies not disqualify for a prize. When writing use one side of the paper only and mention your employer's nome as a guarantee of bona fides. Neither your own nor your employer's name will be disclosed. Payment will be made immediately after publication. Address your letters to The Editor, Thu
COMMERCIAL Moroi?, 7-75, Rosebery Avenue, London, F.C.
Holding a Piston While Turning,
[896] "HAI." (Darlaston) writes :—"I have frequently seen apprentices and learners in difficulties when they have been trying to turn motor pistons. I enclose a sketch—[We have had this redrawn.—End—which shows a slight alteration that may be readily embodied in the design of a piston casting, in order greatly to simplify the holding of such a casting while turning is taking place. A head of convenient size is cast on to the piston, in order to facilitate chucking, and the other end of the piston is mounted on a conical centre, which, in turn, revolves on a centre pin which is mounted in the loose headstock, The method of turning with a mounting of this kind will be readily understood by anybody familiar with the simplest kind of lathe work, and there is no need to deal with the procedure in detail here. An additional advantage of casting the piston with a big head on it is that the casting is cleaner, owing to the rising of the scum in the header, and it also facilitates handling before machining."
A Simple Valve Cutter.
The sender of the following communication has been awarded the 10s. prize this week.
[897] J.C.B." (Dartford) writes :—" I have often seen in your columns descriptions of methods for the reseating of valves. In one case I remember that a driver carefully filed the seating, and I think you will agree with me when I say that a badly-worn and pitted valve seating wants something more accurate than filing to get the face true again. I have myself made a little fitting which will true up an old valve even more quickly than it can be turned in a lathe. I first of all got a piece of round iron bar 2 in. in diameter and 3 in. long. I then drilled a hole directly through the centre to correspond with the stem of the valve ; I next turned a dish out at one end, in order to form a recess at the part where the head of the valve would rest. I next cut two slots opposite each other about half an inch deep and a quarter of an inch wide pointing directly towards the centre. Four 5-16 in. holes to each slot were then drilled and tapped as shown in the sketch—I.We have had this redrawn.—En.jthese holes accommodating 5-16 in. grub screws. I made two cutters out of an old file, taking great care to make them fit into the slots exactly, and also to grind the cutting edges exactly to the angle of the seating of the valve. My tool, with the exception of a tommy bar, was then quite complete, I placed a badly-worn valve in the jig and put its spring on in order to press the Beating against the cutters. A few sharp turns brought about the required result. The compact nature of the tool is its chief advantage."
Clearance in a Closed Crank Chamber.
[898] " G.S.C." (Slough) writes :—" I send you herewith some rough sketches— [We have had these redrawn.--En,—of a novel form of gauge that I made
some while ago. i had to put some experimental fit
tings inside an engine base chamber, and these fittings bad to clear a certain point on the connecting-rod bigend by about 1-32 in. As the base chamber in question had DO inspection doors fitted, the interior was inaccessible when the engine was erected. I was rather puzzled for a while as to how to find the position for the fittings, but I eventually hit on the idea of the gauge about which I am writing to you now. "In the sketches I have shown a section of the bottom half of the base, with the crankshaft, connecting rod and gauge in position. The gauge (A) consists of a sheet of stout tin plate cut to the shape shown. Two small projections are left to register in the base, and from a point central to this, a half circle is struck at such a radius that the crankpin would be cleared by it. From the same point a vertical line is struck, and at a suitable height along this a slot is cut, This latter is equal in length to the stroke plus the diameter of the gudgeon pin, and its width should be a sliding fit for the gudgeon pin. The method of using this gauge is clearly shown by the sketch. The gudgeon pin is put into the connecting rod, and the gauge is put on the base. The pin works in the slot. A scriber is clamped on to the connecting rod at the point which it is necessary to clear. The point of the scriber is kept against the gauge, and if the crank be now rotated, a line will be scribed on the gauge showing the exact position of that particular point throughout the travel of the connecting rod. When I had obtained this marking, I made another gauge, as shown above. I was then able to put in my fittings, and, by checking them as shown, was able to be absolutely certain as to the correctness of their position. This will perhaps seem rather an elaborate way of proceeding with the job. but I knew that if the fittings were not in the exact position which they should occupy, the big-ends would not hold up for any time at all. Moreover, there was the not remote chance of a scrapped base chamber."
About Communication Cords.
[899] "G.W." (Sunderland) writes :—" With reference to the campaign which is being waged with a view to the making of it compulsory to fit communication cords on all heavy motor vehicles, I should like to advise you that I have had such a fitting on my wagon for some time past. I put a bit of in plate on to the underside of the roof of the cab, and I fixed up a knocker, made of a piece of in. plate, on one end of which I had fastened a round knob, and on the other I had arranged for a pin, so that the whole thing could be binged. A piece of cord running over suitable pulleys was easily rigged up to operate this contrivance. The man on the trailer gives one rap when I have to keep to the left, and two sharp raps for an immediate stop. I think that everyone who uses a trailer should have .a communication. cord fixed, as the cost is so very trivial, and the possibility of saving damages is a large one. I drive a five-ton Foden wagon belonging to Robsons, millers, of Sunderland, and the machine is giving us very satisfactory service so