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).
Investigation into an engine 'boom' noise in S.S. and 21-EX cars, attributing the cause to gearbox amplification of engine vibration.
| Identifier | ExFiles\Box 69\4\ scan0260 | |
| Date | 5th July 1929 | |
| X8770 Expl: Dept: Messrs. Rolls-Royce Ltd., Derby, Angleterre. 5th. July 1929. Messrs. Rolls-Royce Ltd., Sevres, Paris, France. X7770 X8770 Mr. Hancock from Hs{Lord Ernest Hives - Chair}/Rn.{Mr Robinson} Sales have severely criticised S.S. cars in general and 21-EX car in particular because of the boom which comes from the engine at speeds round about 50 m.p.h. on top gear. The boom is clearly an engine noise as it is also present at 40 m.p.h. on third speed and 28 m.p.h. on 2nd. You will remember that we suspected that it was an exhaust boom, but since then we have done a number of tests which prove that this is not the case. The most convincing test we have done is to remove the cyl. head on 9-EX car and 19-EX car and tow them. We found that while the engine appeared to be equally rough at the periodic speeds in question, the noise that can be heard in the driving seat on the SS.{S. Smith} is enormously greater than the noise which can be heard in the driving seat of the Phantom. We are therefore forced to the conclusion that the trouble which Sales complain of, is due to the gearbox amplifying the engine vibration which has always existed in the Phantom engine and is now causing a boom in the front seats. As we are very concerned with this noise, and 21-EX car was the one which Sales specifically tried and condemned contd:- | ||