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).
Research engineer's report on engine after-firing, crankshaft vibration damper, and overdrive gearbox issues.
| Identifier | ExFiles\Box 158\4\ scan0280 | |
| Date | 14th December 1938 | |
| W.A.Robotham. -2- 14.12.38. trouble of this sort occurred shortly after the adoption of the downdraft manifold and there had been no other change in the engine which would account for this trouble. Checks made on a particular engine with both the downdraft and up-draft indicated that it was the mixture in the manifold that was making the difference rather than any change in valve temperatures. In other words, if conditions are such that just before the engine comes to a stop the cylinders are furnished an explosive mixture, several explosions may take place before the engine stops. A "good" engine, as regards after-firing, is as likely to be good because there is a poor mixture in the manifold rather than because of better than normal cooling of the valves. In some experiments that were made with the sodium-cooled valves, we found that these valves gave a great improvement when the engine was shut down immediately after operating for a time at full load at 3800 r.p.m., whereas the improvement was negligible if the engine were operated at 1,000 r.p.m. before the ignition was turned off. As to the crankshaft vibration damper, we have had very little trouble which might be ascribed to too small an amount of rubber in the driving cone. We have encountered trouble from time to time due to the use of a poor grade of rubber and at one time, with an earlier design, experienced a considerable amount of rubber destruction as a result of the running out of the damper after a moderate amount of operation at high speed. Since installing the bakelite sleeve, which tends to guide the damper flywheel and hold it central, there has been very little evidence of insufficient damper life. As for the overdrive gear box, we make no provision to prevent drivers operating in direct gear thru the kickdown at high speeds. It is realized that this may occur occasionally but there is a distinct noise due to the action of the solenoid when the "kickdown" is operated and I believe that it will be very rare that an operator will leave the car in direct gear, even though he may at first occasionally operate the kickdown accidently. Yours very truly, S.W.Sparrow. Research Engineer. SWSparrow/MCA. | ||