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).
Guide on the maintenance, troubleshooting, and adjustment of a magneto's contact breaker.
| Identifier | ExFiles\Box 4\5\ 05-page037 | |
| Date | 20th February 1912 | |
| THE MOTOR, February 20th, 1912. How the Magneto Works. right position is repairs to the armature. This also applies if you have removed the contact breaker to clean it, or for any other reason.” “How am I to know if it is in the right position?” “If you will turn it over and look at the back of the base plate you will see that there is a taper central boss which goes inside the end of the armature-shaft. This boss is formed with a little key, and the hollow in the armature shaft is made with a little slot to correspond (see fig. 6). In replacing the contact breaker you must see that the key goes into the slot. When in this position the contact breaker is replaced correctly, and the central screw can then be tightened.” “There does not seem much difficulty about that.” “The most important part of the examination is to see that the surfaces of the platinum blocks, where they touch one another, are clean. After long usage they are liable to turn black and become rough, or ‘pitted’ as it is called, and they must be made smooth again. Accessory makers supply small files for this purpose, and probably the makers of your magneto will send you one if you write to them. These files are very small and fine. It is not necessary to remove the parts to use the file, as it can be slipped in between the platinum surfaces and rubbed backwards and forwards so as just to remove the dirty pitted surfaces. Platinum is a very expensive metal, so you must not file away more than can be helped. Half a dozen strokes with a fine file are all that are really required. If the surfaces are merely oily the best thing to do is to dip a small strip of paper into petrol and then press the fibre block so that the platinum surfaces are separated. Then slip the paper into place, release the fibre block so that the paper is gripped, and draw it out gently. The pressure of the spring causes the platinum blocks to grip the paper strip firmly, and the petrol removes the oil and dirt from both surfaces. When the paper strip is removed separate the fibre blocks again, so that you can see both surfaces and make quite sure there is no paper left between them.” Fig. 15.—Separating the platinum points of the contact breaker rocker. “Anything else?” “In very damp and foggy weather I have once or twice found the engine would not start, and on examination I found that the contact breaker rocker was tight on its pivot, and even stuck wide open, the spring not being strong enough to bring the blocks in contact with one another.” “What is that due to?” “Well, the pivot of the bell crank rocking lever is lined or ‘bushed’ with fibre. In the very damp Fig. 17.—Testing the gap of the contact breaker by means of a gauge, whilst the platinum points are held apart by the rocker being on the cam. weather the moisture reached this fibre and caused it to swell so that the bearing at this point was tighter than it should be. If under similar conditions your engine fail to start it is worth while, after having satisfied yourself that you have turned on the petrol and switched on the current, to see whether the contact breaker is quite free.” “How should I do that?” “Merely press the fibre block with the finger, as shown in fig. 16, and see if the rocker moves backwards and forwards quite easily.” “The rocking lever looks fairly strong, but the spring is comparatively thin.” “True, but it very rarely breaks. If you want to be on the safe side with regard to the magneto it might be advisable to obtain a spare contact breaker complete. Then if the spring should break or the rocker stick you can undo the central screw and remove the existing contact breaker and fit your spare one.” “Will it fit my magneto?” “Certainly. All these parts are made absolutely interchangeable, provided you specify the right type of magneto when ordering.” “You say the contact breaker requires correct adjustment. How am I to know when it is correctly adjusted?” “Turn the armature round until the fibre block is in the middle of one of the steel blocks. The platinum blocks are now separated, and the distance that these separate must be nearly correct. The distance is half a millimetre.” “Yes, but how am I to measure that?” “Each magneto maker supplies a gauge, and as a | ||