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).
Distributor performance, focusing on spark variation between cylinders for Delco and RR models, and the resulting engine detonation and noise.
| Identifier | ExFiles\Box 168\3\ img076 | |
| Date | 14th February 1939 | |
| - 2 - Rm{William Robotham - Chief Engineer}/CTS.{C. Trot Salt - Carburation}1/G.14.2.39. [Handwritten: Wide scatter in the spark.] We understand from Rm{William Robotham - Chief Engineer}/Childs, that the difference in 'make and break' ratio, between the two distributors could account for a longer duration of high voltage spark in the case of the Delco, by virtue of the two contact breakers. Our Laboratory work to a limit of ± ½° on their rig, which running at half engine speed means ± 1° crankshaft degrees. This is satisfactory, because we cannot work to any finer limit ourselves in checking distributors on the engine. Our recording device, for the spark position, is taken through the spring drive, which gives rise to a certain amount of oscillation. We find, however, that there is considerable variation between cylinders on both Delco and RR. distributors. Graph S.73 shows this variation to be as much as 5° (crank) on the particular Delco Remy on test. This had been synchronised in the Laboratory, and was not interfered with on test. This point requires investigation, and is important because the effect on the road will be to bring in odd cylinders detonating, with ignition set on the border line of detonation. The phenomenon would be most noticeable on a high compression engine, where actual 'border line' detonation becomes more sensitive, and uneven spark distribution is not conducive to a smooth engine. NOISE. The particular RR. distributor on test is quieter than the original design we tested six months ago, but is not as quiet as the Delco. With reference to initial setting and adjustment of the RR. distributor, we would say that this point was dealt with at some length in our report on the original design. The slight modification incorporated in the distributor now tested, cannot be looked upon as much of an improvement in the light of our previous report Rm{William Robotham - Chief Engineer}/F.Potts.1/AP.12.4.38. We would point out, that the removal of the cam, cannot be carried out with the existing withdrawal tool, because the tool depends upon a projecting spigot which does not exist in the latest design. We have pointed out before, that to remove the cam by levering a screw driver beneath it, is bad practice, because the centre shaft can be bent. The effect of running with a shaft that is only a few thous out of truth, will cause a bigger variation still between the relative spark position on different cylinders. Actually, there are few people left in the factory, who are capable of setting the ignition by this method to anything nearer than ± 2°. | ||