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).
The failure of a Bentley Stabilising Bumper Bar and subsequent design modifications.
| Identifier | ExFiles\Box 118\2\ scan0236 | |
| Date | 8th November 1935 | |
| X1023 To Hd.{Mr Hayward/Mr Huddy} (FOR DEPOT SHEET) Hs{Lord Ernest Hives - Chair}/FJH.{Fred J. Hardy - Chief Dev. Engineer}28/KW. 8.11.35. Bentley Stabilising Bumper Bars. A case has occurred recently of a Stabilising Bumper Bar falling off a Bentley car during a 10,000 miles test in France. The method of fixing was of the early type in which the stud passed through a clearance hole in the dumb iron and was screwed and taper pinned into a square nut on the inside of the dumb iron. The failure was not due to fracture of the stud, but to its working out of the square nut. This was possible because when the bumper bar was fitted the taper pin had been sheared in the following manner. The stud had not been screwed completely home in the square nut before the taper pin was fitted, with the result that the outer nut securing the bumper bar had come to the end of its thread and further tightening had screwed the stud further into the square nut and sheared the taper pin. The attached sketch shows the parts concerned. With the present method of fixing in which the square nut is deleted and the stud is screwed and pinned directly into the dumb iron, it would still be possible for this to happen if the stud were not screwed right home in the dumb iron. Will you please ensure that this does not happen on production chassis, by making sure that the stud is screwed right home and seeing that there is sufficient thread on the stud for the front nut. For chassis already in production the detail drawing of the stud has been altered to give a greater length of thread at the front end of the stud, and for future production there is a modified scheme, N.Sch.4676, in which a shoulder on the stud takes the tightening load of the front nut. Hs{Lord Ernest Hives - Chair}/F.J.Hardy. | ||