Contributions from Drivers and Mechanics.
Page 21
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Ten Shillings Weekly for the Best Communication Received, and One Penny a Line of ten words for anything else published.
Drivers of commercial motor vehicles 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. Long and successful rails; services with no "lost journeys" ; workshop tips and smart repairs: all are suitable subjects. Send a post.card, or a letter, or a sketch to us—no matter how short, or how written, or how worded. We will "knock it into shape" before publication. When writing you must mention your employer's name as a guarantee of bona fides (motto:. publication), and you should stale whether you wish your own name, or initials only, to be published. Payment will be made immediately after publication. Address your letters to he Editor," THE COMMERCIAL
Mcrae," 7-15, Rosebery Avenue, London, E.C.
To Grind in Valves.
L:538] "A.H.H." (Cardiff) writes :—" Perhaps the following short description may interest drivers and mechanics. I have generally found that the ordinary screwdriver is too clumsy to he used for valve grinding. In its place I always now use a special tool I have knocked out. I found an old starting-handle spindle which had once belonged to a Dennis chassis. I cut this off to 8 inches long, turned the two ends to 5-16th-inch diameter for a length of 3e inches at one end and of I inch at the other. The long end I hammered into the shape of a screwdriver and this I hardened at the point. The middle of the shaft I left at diameter. The short 5-16th-inch end I made to fit a small belly-brace. Thus fitted out and with a small quantity of Carborundum am able to save a good deal of time and physical fatigue."
At the Top of ths Stroke : Ignition Timing.
The sender of the following communication has been awarded the 10s. prize this week.
[5391 " T.W.T." (Mortlake) sends a description to us of a device which he has found useful for the timing of petrol engines :—" It sometimes happens that the ignition and valve gear on a. petrol engine has to be retimed. This ie a matter of no great difficulty, providing that the engine fly-wheel be plainly marked to show the positions of the pistons or that the crank-chamber he fitted with easilyremovable inspection doors. In many cases, however, no such means are available for ascertaining when the cranks are at the top or bottom of their strokes. In such circum
stances a timing wire is, when possible, inserted through the compression tap at the top of the cylinder. When such a tap either does not exist or is so choked as to be unavailable, advantage may often be taken of the ordi
'Lary ignition-plug hole situated in the side of the combustion chamber. For this purpose I have procured the metallic body of an ordinary ignition plug, and I have made a small disc of brass or other suitable material which could be pivoted inside the plug body in such a way as to swing freely. I have then passed a wire, as shown in my sketch [We have had this redrawn.--ED.] through the disc, out of centre, and have well soldered it into position. A small weight on the inner crooked end of the wire will ensure its following the piston. When this fitting is screwed into place in the plug hole, it will be realised that, as the piston rises, the outside or visible end of the wire will fall until it reaches a fixed lowest point. This will indicate that the piston is right on top of its stroke. If the wire be pivoted at its middle point, the travel of the piston will be accurately indicated by the outer end of the wire. It will thus be a simple matter to set the magneto or other ignition detail accurately to any point before or after the top of the stroke. The old method of thrusting a straight wire through any available hole in the top of the cylinder is, of course, well-known. and it is so useful that the modification which I have described may, perhaps, be welcomed by some of the readers of your most useful weekly page of tips for drivers and mechanics."
New Brake Bands.
5401 " K.S.K." (Seville) in the course of a long letter writes :--" I am often surprised to find how seldom a repairer will make a good job of fitting a new set of brake bands. When the shoes, which are to be attached to the bands, are to be of gunmetal or east-iron, as there is practically no spring in these materials the brakes will require to be very carefully fitted. Very little clearance will be wanted. When wooden blocks are to be used the clearance should be greater, as the whole band will then be more flexible and will be more liable to drag. Usually the bands themselves break near the ends, very often through some rivet hole which has been drilled, too close to the end. Frequently the blocks are brought too far round the band, so that when the brake is applied the band itself is subjected to severe local bending just where the end blocks finish, and that is where breakage is bound to occur. It is very necessary to get the bands the correct length ; this can be done quite easily by carefully laying out the strip metal on edge against a templet or a marked board. Personally I have had excellent results from copper lining blocks, and I have successfully used three or four sheets of strip well riveted together for the band, In place of one thick and consequently stiff strip. For commercial vehicles I would always prefer loco-type brake blocks in place of band brakes if I could get them. There are very few band brakes which act quite satisfactorily on flue reverse. I must try these new brake-lining fabrics I have heard about."