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).
Illustrated article from a magazine detailing the components and workings of a magneto's contact breaker.
| Identifier | ExFiles\Box 4\5\ 05-page036 | |
| Date | 2nd November 1912 | |
| THE AUTOCAR, November 2nd, 1912. so this in the case of the Simms and the Bosch mag-netos you first move sideways the spring blade which holds the contact breaker cover in place. The cover can now be removed exposing the contact breaker [Image of a contact breaker ring] Fig. 7.—Adjustable contact breaker ring of Eisemann magneto, showing the internal cams. Labels on image: ADJUSTABLE RING, LEVER, CAMS. (fig. 5), which looks rather intricate, but is not as bad as it looks. It comprises (see fig. 6) a rocking lever of bell crank shape and pivoted at its centre to a base-plate, which is fixed by means of a central retaining screw to the armature. We will now further expose the contact breaker by removing the adjustable ring (fig. 5) which surrounds the contact breaker. This is done by merely pulling this ring from the magneto (fig. 7). In the case of the Eisemann magneto the amount of force necessary to remove the contact breaker is greater than in the other cases, as spring retaining devices are provided. Also, as you see (see fig. 8) in the Eisemann magneto, the cover has two spring catches, one arranged on each side. These have to be pressed together and then pulled away from the magneto. This removes the contact breaker cover plate. The adjustable ring can then be withdrawn. The actual contact breaker in all the three magnetos is the same, the only difference being in the manner of attachment of the covers. To make the matter clearer we will undo the central screw and remove the whole contact breaker. Directly you try to undo the screw the armature revolves, so we have to hold the other end of it. When the screw is removed the contact breaker can be pulled outwards away from the magneto. It is generally rather stiff, but a straight pull does the trick. The contact breaker when removed looks much simpler than it does when in place (see fig. 6a). You will notice the bell crank lever is provided at one end with a fibre block, whilst at the other end it carries a platinum block. There is a curved spring attached to the bell crank lever, anchored at the other end to the base plate, and this presses the platinum block down on to another platinum block formed on the end of an adjustable screw, which is secured to the base plate. If you press the fibre block with the finger the platinum points will be separated. How the Magneto Works. What is that little spring blade which presses down on the centre of the bell crank lever? That is merely a spring which holds the bell crank lever on to its pivot, as you will see if you press the spring away from its position. It is merely a simple means of securing the rocking lever in place. Now each time a spark is required for the engine ignition the platinum blocks move apart. How is that done? If you will look at the adjustable ring (fig. 7) which we have just removed, you will see that it has fixed to it two steel blocks or cams arranged opposite to one another, the ends of which are bevelled. You will remember that the contact breaker is fixed to the armature by means of the central retaining screw. As the armature revolves it therefore rotates the contact breaker, with the consequence that the fibre block at the end of the rocking lever strikes the bevelled steel blocks or cams, which are stationary. There being two of these cams equally spaced, for every revolution of the armature (and therefore of the engine), the contact breaker platinum points separate twice, and, as each time the contact breaker works the current passes out of the armature to the slip ring, you will see that the ignition mark is provided twice per revolution. [Image of a distributor end] Fig. 8.—Distributor end of an Eisemann magneto. Labels on image: SPRING CATCHES, EARTH TERMINAL. [Image of a distributor and contact breaker] Fig. 9.—Distributor and view of a Simms magneto with the contact breaker removed. The latter is shown below, face downwards, so that the integral key can be seen on the base plate. Labels on image: CONTACT BREAKER, BASE PLATE. Does the contact breaker give any trouble? Not if it is properly looked after. By that I do not mean that it requires a lot of attention, as doubtless you have gathered from the fact that you have driven your car two or three months without touching the contact breaker. From this you will see that it does not often require attention, but to save trouble on the road it is advisable to take off the cover occasionally and examine the contact breaker. Well, I might examine it all day without being a bit the wiser as to whether it is likely to go wrong or not. How can I know whether it is likely to give trouble? In the first place, the central retaining screw must always be screwed up tightly. It is pretty certain to be tight at first, but if you remove the contact breaker at all be careful to see that the screw is screwed up tightly. The contact breaker must also be in | ||