The Motor Drivers News.
Page 27
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Inefficient Drivers.
" J.D." (Keighley) says : " I seem to have got known through writing to this page, as only a week ago an employer called me into his engine shed to look at his steam wagon. He referred to a few hints taken from these pages, and, as someone had told him I was the writer, he asked me if I could explain to him how it was his engine required a great lot of fuel, and water, in excess to what it did when the vehicle was new. The driver also complained of bad steaming of the boiler, and indifferent hauling power. I enquired from the driver whether the slide valves had become displaced. He replied that he could not tell, as he never thought to look. I, also, asked him if he had examined the piston rings, but he gave the same reply. Being busy myself at the time, I promised his employer, that, if he was willing, I would come on Sunday morning, and examine his engine. This was on a Friday so he had not long to wait. The driver got all covers removed, and everything nicely cleaned. I found, on arrival, that the slide valves were badly set. I examined the link motion, and, finding this in good working order, I began to re-set the valves, trying, at the same time, to impress the theory on the mind of the driver while doing so. I next turned his attention to the h.p. cylinder, and, after removing check nut, and piston block, I found one ring in a mangled condition, whilst the other was ground into pellets. The driver could hardly believe such a thing should occur. I found the piston was out of its place, as, when the crank was on one of its centres, the steam entrance to the cylinder was overlapped by the piston ; this was caused by the big-ends being packed at one end of the brasses, instead of the packing being equally divided at each of their ends. I pointed out these defects, and we set about remedying them. Several similar cases of ignorance on the part of drivers of steam vehicles have, lately, come under my notice."
Trouble with a Magneto System.
"S.O.B." (Hampstead) sends an illustrated letter re ignition :---" The following defect in ignition may occur at any time, and on almost any car, so I think the subject is worthy of a little space in the Drivers News ' columns. A few days ago, I was out testing a motorbus that had been overhauled, and which was fitted with low-tension magneto ignition. The lead from the magneto was carried to a very common type of distributing box, fitted with tell-tales for each cylinder, and screwed to a light iron bracket, kept in position by the yoke holding down the valve covers. After I had taken the car for a good run of, about, twelve, or fourteen, miles, I detected a slight mis-firing, which, gradually. became worse, so that I had to stop, and investigate. I had a casual look round the ignition, and, then, tried to start the engine. Little faults are more easily discovered when the engine is running than at other times. I found, however, that I could not get a single explosion, so I examined the timing, which I found all correct. I disconnected the magneto lead from the distributing box, and tested the magneto alone, and found it sparking all right, so, I connected up again, and then removed the covers from the inlet valves, to enable me to see the make, and break, contacts. On turning the engine, I found that there was no spark at any of the four contacts. Once more, I disenn nected the magneto lead from the distributing box, and connected it to each contact pin, and, on the engine being
turned round, each igniter gave a fat spark. From that, it was obvious that the distributing box was at fault. As it was getting dark, and I had no lights on board, I roughly bunched the four plug leads direct on to the magneto, and reached the garage all right. On arrival at the garage, I took the distributing box to pieces and there found a very interesting, and very simple, cause for the trouble, which will be more easily understood from the accompanying sketch. A is the body of the distributing box, constructed from mahogany. B is the bracket to which the body of the box (A) is screwed. C is the wire which connects the two switches (D) which receive the tell-tale pegs. E is a screw holding one switch to the inside of the box, and F is a screw holding the box itself to the bracket (B). It will be noticed that the two screws come very close together, and they are hidden away in the woodwork. When I took the box to pieces, I found the wood surrounding E burnt away (as indicated by dotted line) as far as the screw (F), which, of course, is in direct metallic contact with the engine. Now, the current found this an easier path back to the engine than through the switches, and leads, to the igniters, and, conse
quently, it never reached the tiring points at all. The cause for the burning away of the wood is, I think, the most interesting point. The wire (C) should have been of copper, and of fairly large section, but, instead, it was of iron, or some other metal, and, being of a small section, it offered a high resistance to the current, therefore, getting very hot, and heating the screw (E), with the above result. It will be seen that the wire acted exactly as the platinum filament in an electric incandescent lamp. The two screws, of course, should have been farther apart in any case, but, all the same, the heat should not have been present."