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).
Engine testing regarding oil control, spark plug gaps, ignition systems, and timing to resolve unstable running.
| Identifier | ExFiles\Box 36\2\ scan 188 | |
| Date | 10th October 1928 guessed | |
| contd :- -4- trouble as we can with reasonable certainty control the oil consumption by means of the amount of rubbing surface of the 'Perfect Circle' type of scraper ring. When preparing another engine we should go to the full extent of this control. The Lodge A.40. plugs used appear quite suitable for this work but should be adjusted with not more than .010" gap as we found that on the average this increased to .025" at the end of the 100 hrs. We have previously proved that the gap, to a considerable extent, controls the range of weakening possible before unstable running is manifest. While with a larger gap it is possible to reach the stage of max. economy we run much nearer the unstable region and any fluctuation in speed runs us into this region and is attended by popping and missing. Unbraided high tension cables are essential we have proved by experiment, as the metallic braiding considerably reduces the energy of the spark and means that if the plug gap increases our mixture range in the weak direction is considerably reduced. We have also found during the duration test that the max. energy given by the magneto appears to be in about the half retard position at which position it is much better able to deal with increased resistance at the plugs through oil. For this purpose we think the position of max. energy should be accurately determined and the timing set so that we work within this range over the throttled range. We have found that when running throttled an inlet plug becoming oiled up, gives more trouble through popping when running weak than an exhaust, due no doubt to the contd :- | ||