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).
Investigating coil ignition misfires and spark plug gap issues on the 20/25 HP chassis.
| Identifier | ExFiles\Box 181\M13\M13.2\ img078 | |
| Date | 3rd August 1931 | |
| To R.{Sir Henry Royce} from Hs{Lord Ernest Hives - Chair}/HEW. c. Sg.{Arthur F. Sidgreaves - MD} Wer. c. Rg.{Mr Rowledge} E.{Mr Elliott - Chief Engineer} c. Ey. Da.{Bernard Day - Chassis Design} ORIGINAL Hs{Lord Ernest Hives - Chair}/HEW2/AM 3.8.31. X6095. COIL IGNITION ON 20/25 HP. CHASSIS. We have been trying for sometime to eliminate misfires on the full load "pick up" on the 20/25. A partial cure was effected on production by closing up the sparking plug gaps to .020" but when the coil has been thoroughly heated up occasional misfires from 5 to 20 m.p.h. on top gear "pick up" still persist. It has been thought that "building up" in the induction system was the sole cause of this "lumping" at low speeds under full load, but the fact that reducing the spark plug gap partially cures the trouble, would appear to negative this explanation, and we have now shown by a series of coil tests that it is fairly definitely due to the inability of the ignition coil to cope with the extra high pressure conditions in the cylinder which occur with a full load pick up. This was also shown to be the case by Dr. E.A. Watson of the M.L. Co. some time ago when he carried out plug voltage tests under varying conditions on a Rover car, and we have similarly proved that these extra high voltages exist at the spark plug by measuring the voltage across the plugs on a 20/25 when running on the road. We could possibly cure the trouble by reducing the plug gaps to .010" but we consider this a retrograde step because the closer we make the plug points, the worse for slow running and the more critical will be the correct adjustment in customers hands, and we have already had cases of ignition trouble in customers hands due to the plug point gap not being properly adjusted. We feel that our battery ignition would give more satisfaction with customers on 20/25 cars if we made the coil powerful enough to deal with all sparking plug conditions particularly where the plug gap has not been set accurately. We have carried out a number of road tests on 18-GIV fitted with a Japan engine, with ignition coils of various makes in order to find out the coil which gave the best performance under the conditions previously described. The coils tried were all up-to-date samples of modern practice with outside primary winding and no ballast resistance, as | ||