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).
Failure of 3 1/2 Litre Bentley valve springs and recommending a design improvement.
| Identifier | ExFiles\Box 88\4\ scan0061 | |
| Date | 11th May 1934 | |
| c.Hs.{Lord Ernest Hives - Chair} c.Wex. X 254 BY.2/J.11.5.34. 3 1/2 Litre Bentley Valve Springs. We note that you have received a copy of the Laboratory Report H1.2/AG.3.5.34. in regard to the failure of valve springs both on the Bentley car Rm.{William Robotham - Chief Engineer} took to America and also the spring which failed whilst a car was being brought back to these Works from the coachbuilders. It is clearly shewn on this report that there was no defect either of material or workmanship which could be held responsible for the failures which have occurred. We believe it has been suggested in the case of the spring which failed in this country that the wire was faulty, but Laboratory examination shows that this was not the case. In regard to the springs which failed in U.S.A. this might have been caused through the extreme cold experienced at the time the failures occurred, although it must be noted that valve springs both aero and chassis have functioned under similar conditions without giving trouble. The failures therefore would suggest that the Bentley valve springs are probably overstressed. As an immediate improvement, we recommend that these springs should be produced in the same manner as the old Silver Ghost type of taper valve spring, i.e. with a graduated distance between the coils designed so that the whole of the coils closed down simultaneously. As the spring is produced at the moment with equal distance between the coils, it means that the larger coils are closing and becoming choc-a-bloc before the smaller ones at the top end of the spring. BY RM{William Robotham - Chief Engineer} P.S. We understand that as a result of the examination carried out on the broken springs in America, Rm.{William Robotham - Chief Engineer} concurs that no fault could be found with the material or with the heat treatment. | ||