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).
Series of experiments to reduce engine noise on a 1-B-IV Bentley car.
| Identifier | ExFiles\Box 138\1\ scan0174 | |
| Date | 10th May 1935 | |
| To Sg.{Arthur F. Sidgreaves - MD} & Wor{Arthur Wormald - General Works Manager}: c. to E.{Mr Elliott - Chief Engineer} c. to By.{R.W. Bailey - Chief Engineer} c. to Ex. c. to Bx. Bentley Engine Noises. We have been carrying out a series of experiments on the engine of 1-B-IV car, with a view to "deadening" the engine noises, such as tappets and timing gear rattles, which are so noticeable when standing at the side of the car with the engine idling. Our method has been the further use of felt encased in thin sheets of aluminium, to cover the top and both sides of the engine. We arranged first of all an additional flange on the cylinder head to carry a second rocker cover entirely covering but not touching the present rocker cover. This cover quietened the tappet noises appreciably, but there was still plenty of noise coming from the cylinder head, cylinder block and top half crankcase, and it seemed that if one quietened noises at one particular point on the engine, they still found their way out and remained objectionable at other points, and so we made up two covers one to each side of the engine, entirely covering the cylinder block from the rocker cover to the crankcase. These covers had the effect of still further reducing the audible amount of engine noise. We then plastered the timing case with asbestos (first made plastic by immersing in water) and this also considerably quietened the knocks and rattles from the timing gears. 1-B-IV engine unit is a very old one and much more noisy than a production car, but the results obtained lead us to believe that suitably designed and fitted covers would result in an approximately 50% quieter Bentley engine, of which figure we apportion 20% to the extra rocker cover and 10% each to the side covers and damped timing case. We realise that we possibly could not cover the timing case with any sort of material because of trouble with oil temperatures, but we could fit metal strips or even cast them in the case so as to reduce the "sound box" effect which our present timing case gives. In addition, the fitting of the engine covers gives the whole engine a much cleaner and neater appearance. | ||