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).
Ignition timing adjustments and spark plug experiments for the Big Bore 20/25 HP engine.
| Identifier | ExFiles\Box 101\1\ scan0202 | |
| Date | 18th April 1936 | |
| X5004 To Mx.{John H Maddocks - Chief Proving Officer} Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}5/KW.18.4.36. Ignition Timing - Big Bore 20/25 HP, and Sparking Plugs. This is to confirm that you are going to check over that you are not losing performance by timing your ignitions on the 20/25 by 14°. With the new head we have found it necessary to time the ignition at 18° to 20° to get maximum performance on pick-up. We admit that this increases the roughness of the engine on tick-over, and that you may want to come to some sort of compromise, but we should like to know that your results are in line with ours. With regard to sparking plugs, we admit we have not done this job satisfactorily. Our best results with regard to slow running have been obtained with the wrapped mica type of plug which we have just condemned on the Bentley because it will not stand up to leaded fuels. We have not yet satisfied ourselves that the new plug which we have standardised on the Bentley will give the desired results on the 20/25. The solution for the moment appears to be to carry on with the wrapped mica type of plug for test purposes, while we conclude our experiments. Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} | ||