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 argument against magneto ignition on the Phantom II, focusing on starting difficulties.
| Identifier | ExFiles\Box 182\M19\ img101 | |
| Date | 14th January 1931 | |
| He/AIL. 2/AL.14.1.31. MAGNETO IGNITION ON PHANTOM II. X. 699. The one argument for the battery and magneto ignition when compared with twin battery ignitions is that it should be possible to run the car if the battery is out of action. The slow running properties of the magneto are not comparable with battery ignition and the available range of advance is strictly limited necessitating rather elaborate mechanism for the synchronism of the two ignitions. In quite 80% of cases it is not safely possible to start up a Phantom II car (by means of the starting handle) on magneto ignition after the car has been standing over night even in a well warmed garage. The ignition lever is fully retarded in order to avoid backfires; it is not humanly possible to 'swing' the engine by means of the starting handle, all that can be done is to pull it over each compression as sharply as possible, which will not start up the engine. The magneto invariably fires after the engine has been pulled over to dead centre and the engine runs backwards. There is no risk of injury to the person operating the starting handle because the back fire always takes place well after the engine has turned over top dead centre by which time the starting handle dogs are disengaged. What happens is that the impetus given to the engine by the cylinder compression turns it to the next compression more quickly than it is possible to turn it by the hand. It 'bounces' back off the next compression sufficiently far to cause the magneto points and open then again quickly causing the magneto to fire and turn the engine over backwards. Sometimes the engine will fire three or four times backwards before stopping, very rarely it will fire once or twice backwards and then run forwards. It is very seldom that it can be started at all. If the magneto ignition is advanced it is possible to start up by hand if one cares to take the risk of a damaged wrist due to a back fire. In some cases this happens even with a hot engine, the variation from car to car being due to differences in low speed firing efficiency of the magnetos. This does not occur on a 25 HP. car because it is possible to swing these engines by means of the starting handle sufficiently fast for the magneto to fire. There are other points which do not shew up the magneto favourably in argument against battery ignition. | ||