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).
Investigating a flywheel failure on an Open Bentley caused by engine over-revving.
| Identifier | ExFiles\Box 3\4\ 04-page374 | |
| Date | 1st July 1933 | |
| To Ox. From Hs.{Lord Ernest Hives - Chair} c. to W. c. to C. c. to Sc. c. to Nor. c. to S. Re.OPEN BENTLEY. We are sorry this car went wrong with you as the weather was ideal for enjoying an open car. The failure on the car is the flywheel coming loose. We have had two cases of this previously. In both instances when it has happened before it has been caused by the gear coming out and the engine over-revving to such an extent that it went through the motor period. In the first case the gear came out due to the cushion of the car preventing the top gear going in properly. In the second case the car was being tested on the dynamometer on one of the gears which worked out. We have already decided that it will be essential to put a red mark on the speedometer on the bentley at 4,500 engine revs. The sole use of the engine rev. indicator is to prevent damage to the engine. Previously when we have had engines which gave very little power at high speeds it was not possible to damage them to any extent by over-revving them, but on the Bentley engine it is certain that if 4,500 engine revs. is exceeded there is a risk of either shaking the flywheel loose or shaking the slipper wheel loose, or breaking the crankshaft. The fact that the Bentley engine will rev. up without any noise and fuss makes it possible that on low gears the engine can be over-revved without the driver realising it. It is for this reason that we intend to mark the rev. counter. The fact that the car went wrong in your hands has satisfied us that a similar failure could occur in the hands of any customer. It is possible on this car as the flywheel has come loose before, that it was not in a perfect state when we left you the car or it is possible that on our run down to Brooklands, or at Brooklands, we may have started the trouble. We should however be interested to hear from you whether there were any occasions when you ran up to the maximum engine revs. on low gears. The rev. counter fitted to the car was reading about 5% low. It has already been agreed that we shall alter the flywheel fixing and we are proposing to fit up the open car with a flywheel fixing which it is intended, to use on production. We would like to send this car back again to you on Friday night so that you can run it for the weekend and give us | ||