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).
Pros and cons of belt drives versus chain drives for engine auxiliaries.
| Identifier | ExFiles\Box 133\2\ scan0180 | |
| Date | 9th November 1935 guessed | |
| (2) With the machine on the exhaust side of the engine, however, and a three corner belt drive which we have set out, it is unfortunate that the direction of rotation causes the fan to be driven after the dynamo, which means that the heavy tension of driving the fan at top speed has to pass round the small pulley of the dynamo, which is not so good for the belt and the dynamo bearing. We have, therefore, not got an ideal and easily applied scheme at the moment to offer. The thing that I personally object to is any attempt at driving the water pump by a belt. With the water pump stopped the car is stopped also in the event of a failure of the above drive, and this is certainly very serious. It is, however, standard practice today on nearly all American and European cars, including the leading makes, to drive both the water pump and the dynamo by belt. I certainly would not advocate such a scheme. With regard to the question of chain drive, it was suggested at one time the Wraith engine should be made with both gears and chains alternatively, but it was very soon apparent that this was not possible because the requirements with regard to centre distances are too different, and the Wraith was, therefore, finally arranged with a silent chain drive in which the water pump was driven in tandem with the dynamo. Our experience is that the chain drive achieves a very good standard of silence, but that the chain wears out and requires replacement at regular intervals, due to chain stretch. Gear drives on the other hand, although more costly and difficult to get right, achieve a higher standard of silence and do not wear out in the same way. So far as we have gone the Phantom 3 gear drive has given considerable satisfaction. The position as we see it at the moment is that having got rid of the magneto on the big bore 20/25 it then becomes possible to consider one or two alternative schemes, and we are looking into these at the moment to see what recommendations, if any, we could put up. E.{Mr Elliott - Chief Engineer} | ||