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 relative timing of the battery and magneto ignition systems.
| Identifier | ExFiles\Box 37\1\ scan 243 | |
| Date | 17th October 1923 | |
| X3949 To EY. from EFC. c. By/Shn. c. EF. c. Hs{Lord Ernest Hives - Chair}/TMW. EFC2/T17.10.23. X.3485 - RELATIVE TIMING OF BATTERY AND MAGNETO. X1551 X3949 X928 X4357 At speeds below that at which the automatic advance of the battery ignition comes into play, the ignition lever range of the battery ignition, viz. 40°, is from 26 a.d.p. to 14 b.d.p. At the other extreme at which the automatic advance is completed, the hand ignition range is from 4° b.d.p. to 44° b.d.p., the range of the automatic advance being 30°. The ignition lever range of the R.O.K Watford magneto advance is 36° viz., d.p. to 36° b.d.p. Thus with hand lever fully retarded and at speeds below 500 engine r.p.m., at which speed the automatic advance begins, the magneto 'break' is 28° ahead of that of the battery ignition. Similarly for the fully advanced position the magneto 'break' is 22° ahead. The advance allowed by the rotor blade without necessitating a jumping forward of the magneto spark from blade to distributor pin is only 8°, i.e. 16° on the engine. Hence at low speeds and full retard of lever the ignition as at present arranged will necessitate the magneto spark jumping forward the equivalent of 10°, which is 5° on the distributor, or .100" at the rotor periphery. Since the magneto advance is slower than the battery advance, this amount is slightly reduced as the | ||