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).
Bentley Flywheel Fixing issue, potential crankshaft breakages, and proposed modifications.
| Identifier | ExFiles\Box 85\2\ scan0021 | |
| Date | 5th July 1933 | |
| X 212 To WCH. from E.{Mr Elliott - Chief Engineer} E.1/HP.5.7.33. c. Hs.{Lord Ernest Hives - Chair} By.{R.W. Bailey - Chief Engineer} Sft.{Mr Swift} RHC.{R. H. Coverley - Production Engineer} re Bentley Flywheel Fixing. Referring to Sg.{Arthur F. Sidgreaves - MD}11/E.4.7.33, the flywheel coming loose has probably prevented crankshafts being broken under the conditions where we know the engine has run up through the master period. Nevertheless we cannot accept a flywheel fixing which is disturbed under these conditions, and an improved scheme has been issued - LeC.3549 which will be on test tomorrow in which the existing flywheel is machined out and mounted on a centre to fit the existing crankshaft and secured with stronger nuts. BY and Hs.{Lord Ernest Hives - Chair} are in agreement that the scheme to be tested is most hopeful and has an added advantage that the centre being a separate piece from the flywheel can be made in better material to resist fracture when flexing. We contemplate increasing the number of bolts by 50% later but as we have 15 crankshafts finished for the first batch of cars, we are testing out the improved scheme with the existing number of bolts, and will decide this point later. Actually we think from the evidence that the weakness of the existing scheme, which is identical with the 20/25, lies mostly in the thickness of the nuts and the flywheel flange and we should soon know if these points have been sufficiently dealt with We can also put in the next larger size of bolt for these 15 cranks if necessary. In the meantime we have got to accept that the Bentley engine is much more susceptible to damage from over revving than any of our previous products owing to the smaller margin between the valve gear floating speed and the crankshaft master period. This position is generally accepted on sports cars and is usually safeguarded by fitting an engine speed indicator with a red mark at max safe speed as proposed in Hs.{Lord Ernest Hives - Chair}3/MJ4.7.33 or by a series of red marks on the speedometer, one for each gear ratio. E.{Mr Elliott - Chief Engineer} | ||