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).
The two-spark magneto for the 40/50 HP Ghost chassis, detailing its advantages and correct sparking plug usage.
| Identifier | ExFiles\Box 10\3\ 03-page164 | |
| Date | 3rd August 1929 | |
| T.S.D. Memorandum No. 195/1. 40/50 H.P. GHOST CHASSIS. THE TWO SPARK MAGNETO --------------------------------------------- The two spark magneto which is standardised on all 40/50 H.P. chassis leaving the works after the middle of October 1928, is a development of the single spark magneto of similar construction. Instead of providing only one high tension current, it provides two simultaneous sparks, one in each of the two plugs with which each cylinder is fitted. The advantage of this is that with two sparks occurring simultaneously at opposite sides of the combustion chamber the ignition of the charge is much more rapid and more complete than is possible with only a single spark. Better and more economical running is obtained, particularly at low speeds. The timing and general instructions for the single spark magneto apply equally to the two spark magneto, and it should be noted that the cam ring setting should be 19 degrees for this magneto and that the adjustment of the contact breaker should be .012". We have discovered that it is necessary to use a special type of sparking plug with the two spark magneto to obtain the best results. We recommend the use of Lodge C.3 plugs, and the gaps should be set to .017"-.019". The object of this memorandum is to draw Agents' attention to the absolute necessity of seeing that the correct type of sparking plug is fitted to these chassis, and the gaps are correctly set. We have recently had several cases of complaints of bad running which have been traced to the fact that the original plugs had been replaced by an unsuitable type. | ||