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).
Technical article explaining the function, maintenance, firing order, and timing of a magneto.
| Identifier | ExFiles\Box 4\5\ 05-page035 | |
| Date | 2nd November 1912 | |
| 790 THE AUTOCAR, November 2nd, 1912. How the Magneto Works. The ball bearings require lubrication about once every thousand miles with a few drops of oil put into the oil holes you see on the front end plate, and also at the top near the distributer. Fig. 5.—Simms magneto with spring blade uncoupled and the contact breaker cover removed. Image labels: ADJUSTABLE RING, COVER, CONTACT BREAKER, SPRING BLADE. "What if I put too much?" "It will only leak out through openings provided for that purpose. Well, now, are you 'quite clear so far?'" "Yes. I am quite clear that as long as the magnets are magnetised and the armature revolves in its bearings a current is generated. This current, you tell me, comes out of the armature winding as far as the brass slip ring on the end of the armature. That is all quite clear, and I suppose from the brass ring it goes to the engine in some way. There does not seem to be any great mystery so far, but I notice you have left out all about the 'magnetic field' and things that bothered me previously." "Yes, because an intimate knowledge of them is not necessary to the motorist; it is so to the man who is going to make and repair magnetos. Do you happen to know the order of firing of your cylinders?" "Well, no; but I know they fire one after the other." "So they do, but not in the order you would expect. One would naturally suppose that if the cylinder next the radiator fired first, the second cylinder would fire next, and then the third, and finally the one next the dashboard, but this is not so. If this were the case the engine would vibrate badly, and the best results are obtained by firing in the order 1, 3, 4, 2, counting from either end (see fig. 4). (In a few cases the order is 1, 2, 4, 3, but this is very rare. Daimlers, however, adopt it.) This does not apply only to the magneto ignition, but to all four-cylinder vertical engines with accumulator or any other ignition. The cylinder next the radiator fires first, say, and then the rear but one from that, followed by the one next the dashboard, whilst No. 2 is the last (see fig. 4). After No. 2 the one next the radiator fires, followed by No. 3, and so on. Is that clear?" "'Quite.' It is only necessary to remember the numbers 1, 3, 4, 2. Are the cylinders marked?" "Not as a rule, but you can very easily mark them. It is usual, though not universal, to count from the radiator end. It is well to note the order of firing, so that if the magneto be taken off it can be connected up properly so that the cylinders fire in the right order, otherwise the engine will not run." "You said you would tell me what troubles are likely to occur with the various parts. You have explained to me about the magnets, now what is likely to occur with the armature?" "The armature will not give you any trouble, and you can ignore its existence. The brass slip ring must be kept moderately clean. To clean this it is not necessary to take the armature out of the magneto; in fact, it is distinctly advisable not to remove the armature." "Why is that?" "Well, the magnets deteriorate if the armature be out of place, unless the pole-pieces are bridged with what is called a 'keeper' for the time being. Also in replacing the armature it is necessary that the gear wheel should mesh correctly with another gear wheel which will be referred to later. For these two reasons it is distinctly advisable not to remove the armature. In fact, it is never necessary. I tell you the reasons for not doing this to emphasise the advice to leave the armature always in its place. As you will gather, the armature gives practically no trouble, and requires no attention." "Well, the magnets and the armature seem to be simple enough." "Now we are coming to the timing. You are aware that during each revolution of the engine two explosions take place, the cranks being so set that as two of the pistons are moving up the other two are coming down. Just as one descends on the firing stroke ignition takes place, and during this firing stroke another of the pistons is moving up on the compression stroke ready for the firing directly the first has reached the bottom. It is, therefore, necessary that the current should flow from the magneto to the engine twice per revolution of the armature at equal intervals." "Yes, that seems quite clear." Fig. 6.—Views of Simms (at left) and Bosch contact breakers removed from the armatures and the central retaining screw being shown below. Image labels (left): FIBRE PLATE, ROCKING LEVER, PLATINUM SCREW, SCREW. Image labels (right): SPRING, SPRING BLADE, BLADE or ROCKING LEVER, FIBRE BLOCK. The magneto armature revolves at the same speed as the engine, and at the end of it is fixed the contact breaker. The contact breaker is practically the only part of the magneto which requires attention, and one must therefore understand it quite clearly. For access... | ||