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 a third-speed pinion failure in a Bentley 11 gearbox, with proposed modifications.
| Identifier | ExFiles\Box 86\4\ scan0162 | |
| Date | 20th September 1938 | |
| 228 Da{Bernard Day - Chassis Design}/Hdy.{William Hardy}8/G.20.9.38. c. Rm.{William Robotham - Chief Engineer} GBy 95 in M BENTLEY 11. GEARBOX. There has been a failure on one of the experimental cars of a third speed pinion in the neck of the coupling teeth after approximately 40,000 miles on the road, and 40 hours on 3rd speed on the dynamometer. Consequently, we have investigated the position as regards the over-drive pinion of the overdrive gearbox, and although we think that there is very little risk of trouble in this case, we have made PD.267 attached hereto, which shews an increase in the neck by .020, from .087 to .107, obtained by reducing the root clearance by .005, from .035 to .030, and the length of engagement by .015, from .108 to .093. The proposed root clearance of .030 is a good deal more than is in use on the Phantom lll 3rd speed. This was reduced from .035 to .022 also on account of the weakness of the neck. As regards the suggested length of engagement, this is less than we have used before excepting experimentally in the B.50 box, which has only .075 engagement. We do not think that the reduction of length of engagement will be of any consequence, as there is never any sign of wear of these teeth, and as the reduced clearance is still considerably more than on the Phantom lll it does not seem possible that this can cause trouble. Therefore it seems to us that the increase of strength of the neck shewn by PD.267 should be secured on production pieces at the first convenient opportunity. Da{Bernard Day - Chassis Design}/Hdy.{William Hardy} | ||