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).
Cause of failures in Bentley crankshaft balance weights and proposing design improvements.
| Identifier | ExFiles\Box 85\5\ scan0045 | |
| Date | 29th August 1933 | |
| X217. To WOR.{Arthur Wormald - General Works Manager} from E.{Mr Elliott - Chief Engineer} c.c. Hs.{Lord Ernest Hives - Chair} By.{R.W. Bailey - Chief Engineer} Mr. EP.{G. Eric Platford - Chief Quality Engineer} Bentley - Crankshaft Balance Weights. Referring to the failures in connection with the above, it seems clear that the failure experienced at the Works has occurred due to the balance weight flapping sideways and causing a fatigue fracture at the base of the stud. An examination of the stud left in the crankshaft shows the fracture to correspond with this view. We have yet to examine Hancock's engine but we believe the evidence will be identical. There is no doubt that the design of stud used, which is the same as we are employing for securing balance weights on our Phantom 2 and 20/25 chassis, is faulty for resisting a load of this nature. There is a nasty concentration of stress in the first thread of the stud where it is screwed into the crankshaft. Such a load only arises, however, when the crankshaft is running within the fringe of the master vibration. By using a shouldered stud with a sunken thread and cutting away the middle third of the balance weight face we shall probably improve the job 100%. We are not, however, satisfied with this and we propose to secure the balance weight with two shouldered studs so as to make the job four times as good sideways compared with what it is now. This will not affect the crankshaft forging. E.{Mr Elliott - Chief Engineer} | ||