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 the cause of a 'boom' noise on a Bentley 3-B-IV at 3250 engine revs.
| Identifier | ExFiles\Box 3\6\ 06-page115 | |
| Date | 23th January 1934 | |
| X4553 To Hs.{Lord Ernest Hives - Chair} from Hs{Lord Ernest Hives - Chair}/GWH.{George W. Hancock - Head Chateauroux} HA/GWH.{George W. Hancock - Head Chateauroux}9/KW.23.1.34. Re: Boom on Bentley - 3-B-IV. -------------------------- We have reduced the boom at 3250 engine revs by attention to the following - (1) Silencer mounting was choc-a-bloc. This was made flexible. (2) The front silencer was cracked and had no sliding joint fitted. The latest silencer has been fitted. (3) The rear engine feet mounting: the steel cups for the rubbers were touching on the over-run of the engine. .150" has been taken off the width of the steel cups. (4) Springs have been fitted in place of the rubber in the rear engine mounting. No change was noted by the fitting of the springs but it is possible that springs would be more consistent than rubber. (5) Front torque reaction dampers. There was no load on the dampers. We have tried friction loads of 15, 20 and 30 lbs. The 30 lb. load made the boom slightly more noticeable (approx. 10%). The 20 lb. load steadies the front of the car with no increase to the boom. (6) We are of the opinion that the boom is not connected with the exhaust system. The intensity of the boom with the attention to the above features is very little more pronounced than with the present standard cars when using top gear. Hs{Lord Ernest Hives - Chair}/G.{Mr Griffiths - Chief Accountant / Mr Gnapp} W. Hancock. | ||