From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Article from 'The AUTOCAR' explaining the workings of a magneto for beginners, presented as a dialogue.
| Identifier | ExFiles\Box 4\5\ 05-page033 | |
| Date | 2nd November 1912 | |
| THE AUTOCAR, November 2nd, 1912. How the Magneto Works. A Colloquial Explanation for Beginners. By Eric W. Walford. HELLO, Jones, I hear you have gone in for a car after all. Yes. I have had a car a couple of months now. Well, I am surprised. You always said that a motor car was such a bag of tricks that you would never be able to manage it, let alone understand it. Well I must say I took a good deal of persuading, but at last, I took the plunge and I find what you told, that there were not so many mysteries as one would expect. I certainly was always under the impression that one either had to keep a paid chauffeur and rely on him or have a taste for mechanical and electrical matters. As you know, I am not by any means mechanically inclined, but I have managed to jog along all right with the car up to date. I understand its various parts pretty well with the exception of one item that still remains a mystery to me. What's that? The magneto. The agent who taught me to drive said I need not bother about the magneto, but I do not feel quite happy not knowing anything about it, and I am afraid it may let me down one of these days, and my car has only magneto ignition fired. I do not suppose the magneto will fail you on the road, but it certainly does require an occasional examination in the garage, and you ought to understand the outline of it at any rate. The complete theory and operation of the magneto is somewhat involved. So I gathered. I have relied on various text books for obtaining my knowledge of the details of the car, but when it came to studying the magneto I was completely overcome by the diagrams and the talk of 'magnetic fields,' 'maximum positions,' etc. I felt I was getting out of my own depth, and I could not find any other fellow motorist to explain it to me, so I had to leave it alone. I suppose it is impossible for anybody who has never had special training to understand the magneto? By no means. It is quite simple, and if you live it happens, I have here (Fig. 1) three samples of the leading magnetos, all of similar types, a Simms, an Eisemann, and a Bosch, and also some loose parts. They are all magnetos for four-cylinder engines, and you will see they are all very much alike in appearance, but they differ slightly in detail. In order to make the explanation clear I will show you the details of each. You will notice in each case there are two plates bent over to the shape of horse-shoes. These are the magnets (figs. 1 and 2). They are attached by screws to the brass case of the magneto, which is hollow and has end plates which carry ball bearings for the armature (see fig. 3). The armature itself is out of sight in the complete magneto, but the armature spindle projects, and is provided with a nut and screw thread by means of which it is connected to the engine. At the top, at one end of the magneto, is a vulcanite cover inside which is arranged what is termed the distributor (see fig. 1), whilst below this is a circular brass casing which rocks up and down. This is the contact breaker. All these I will explain fully shortly, but I mention them so that you can get a general idea of the position of the parts. In describing these parts I will also tell you what troubles are likely to occur with each and the remedy, and as far as possible how to prevent trouble occurring. What are the magnets; are they like the magnets one used to play with as a child? The magnets are practically the same as the play-ones, but naturally of a better quality. They are made of steel of a special quality combined with material called Tungsten. The exact composition is of great importance, and is somewhat of a secret. Do the magnets run down? High-class magnets such as are used on a magneto retain their magnetism for a considerable time, but the ordinary toy magnets, being of an inferior quality, soon lose their virtue. How long do the magnets hold out? That depends on how much they are used. I have known a magneto to run 30,000 miles, and at the end of that period the engine would not run quite so slowly as it did originally, and did not start so well, so the magneto was returned to the makers, who remagnetised the magnets, and overcame the trouble. The magnets do not suddenly become demagnetised? No, not unless they receive a blow; a tap with a hammer will demagnetise the magnets instantly, so that if the magneto is taken off the engine great [Diagram Labels] SCREWS SECURING DISTRIBUTOR COVER DISTRIBUTOR TERMINALS MAGNETS SPRING CLIP SWITCH TERMINAL CONTACT BREAKER [Diagram Caption] Fig. 1. - Three types of magnetos. From left to right, Simms, Eisemann and Bosch. | ||