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).
Crankshaft dampers, engine vibration issues, and potential solutions.
| Identifier | ExFiles\Box 132\2\ scan0213 | |
| Date | 24th May 1941 | |
| FILE 1116 To Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden} from Rm.{William Robotham - Chief Engineer} c.c. to Jnr.{Charles L. Jenner} c.c. to Rm{William Robotham - Chief Engineer}/CTS.{C. Trot Salt - Carburation} Rm.{William Robotham - Chief Engineer}8/SW.24.5.41. Crankshaft Dampers. As I suspected when I asked you to make the calculations, we have materially lowered our crankshaft frequency by fitting a Humber Damper. We have done the same thing by making our connecting rod big ends heavier. I should be interested to know how much the increase in weight of our connecting rods is worth in critical speed. I should also like to know what we can do to the Humber damper to reduce the effective inertia of its hub. Presumably without the spring driven crankshaft pinion, the inertia of the cam wheel is bound to have some bearing on the crankshaft critical. We may have to be resigned to the fact that, if we build a 6 cylinder engine with a crankshaft length which is fundamentally suitable for a 4½ litre 6 cyl. engine, then if we wish to run above 4,000 revs. without trouble from the timing gears, we shall have to have our some-what elaborate damped spring drive. One other point is that the vibration which is troubling us, has been shown to be due to the piston inertia, and therefore, we have made matters worse by steadily increasing our piston weights. On our 3½ litre engines, we are determined to get back to our original split skirt piston figure of 16 ozs., since we have practically no evidence that these pistons ever gave trouble in customers hands. If we rubber mounted the fan pulley on the Humber Damper, presumably we might take its inertia out of the system. Alternatively, would the pulley be satisfactory in aluminium? Rm.{William Robotham - Chief Engineer} | ||