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' magazine explaining how to time and set up magnetos for an engine.
| Identifier | ExFiles\Box 4\5\ 05-page044 | |
| Date | 9th November 1912 | |
| THE AUTOCAR, November 9th, 1912. How the Magneto Works. "That is all right supposing there is a coupling on the armature-shaft, but I believe my magneto is fitted with a gear wheel on the armature-shaft which gears with another one on the camshaft. Does it matter if I do not get the gear wheels to mesh together correctly to one tooth?" "Yes, it does. If the armature is a tooth out of position either way the ignition will occur either too early or too late." "How am I to know exactly which tooth is correct?" "Well, there are various ways of timing the magneto exactly. Of course, the gear wheels should be marked so that the correct timing can be seen, but if they are not marked the simplest way is to open the compression taps or take out the sparking plugs and then turn the engine round till No. 1 cylinder is about to commence the firing stroke." "How am I to tell that without taking the cylinder off?" "If you watch the valves as you turn the starting handle round you will see the inlet valve open and then close. As soon as it has closed you know that the piston has reached the end of the suction stroke. When you have turned the handle almost half a revolution further it is near the end of the compression stroke and quite close to the position which we want. Now insert a piece of wire through a valve cap opening of No. 1 so that it touches the top of the piston; then, by turning the handle slowly, you can feel by the piece of wire when the piston reaches the top and stops for an instant before it commences to descend. As soon as the piston has stopped moving it is on what is termed the top 'dead centre.' Make sure that the exhaust valve is not open as the piston rises towards the top dead centre, and then there can be no mistake. The position of No. 1 cylinder is now in the position it occupies when ignition takes place. Now turn the magneto round until the distributer brush is on the segment which you propose to connect up to No. 1 cylinder. Next retard the adjustable ring on the contact breaker to its limit. (At the front of the magneto will be seen an arrow (fig. 24), and the adjustable ring should be moved in the direction of this arrow to its extreme limit.) Now turn the armature round a little distance forward until the contacts are just beginning to break, and then connect up your coupling or bring your gear wheels into mesh. When they are coupled up or in mesh, as the case may be, just see that the platinum contacts are commencing to break, as the coupling may have moved slightly." "It is therefore clear that with the ignition fully retarded the contact breaker is just operating with the piston on the 'dead centre' in No. 1 cylinder and the distributer brush on the segment for that cylinder. Now try the car and take it up a hill on top speed. If the car does not pull as well as it did before, the magneto is not quite far enough 'advanced.' The coupling must be disconnected, or the gear wheels moved out of mesh, and the armature turned a small amount in the direction of the arrow and then be re-connected. It is not necessary to bring the piston of No. 1 cylinder to the dead centre or retard the ignition. We know the position is nearly right, and it is only a delicate adjustment that is necessary. Now try the car again, and if the engine is found to knock with the ignition fully advanced and the car running at nearly full speed, the magneto is probably too far advanced and requires retarding, which is the reverse of the adjustment just described, i.e., the coupling must be unkeyed, and the armature moved Image Captions and Labels: Fig. 24.—Bosch magneto with conductor removed, showing safety spark gap device in its normal position. Labels on Fig 24: SAFETY SPARK GAP, SLIP RING, ARMATURE WINDING, GEAR ON ARMATURE SHAFT. Fig. 25.—Eisemann magneto with high tension conductor removed and the safety spark gap device exposed. Labels on Fig 25: HIGH TENSION TERMINAL, DISTRIBUTER, SLIP RING, SAFETY GAP. Fig. 26.—Simms magneto coupling end. The safety cap is at the end of the magnet instead of encircling the conductor, and is earthed with claws. Labels on Fig 26: HIGH TENSION CONDUCTOR, DISTRIBUTER CAP. Fig. 27.—Testing a Bosch magneto for a spark. The conductor and spark gap are removed, a length of wire being loosely wound round the conductor terminal on the carbon brush holder and carried to within one-eighth of an inch of the magnet. Labels on Fig 27: CARBON BRUSH HOLDER, HIGH TENSION TERMINAL, ADJUSTABLE RING, SAFETY SPARK GAP DEVICE. | ||