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 the cause of a broken rocker shaft on a Phantom III demonstration car.
| Identifier | ExFiles\Box 153\1\ scan0260 | |
| Date | 15th April 1939 | |
| 1380 Sr. Da.{Bernard Day - Chassis Design} Rm.{William Robotham - Chief Engineer} c. Sg.{Arthur F. Sidgreaves - MD} c. C. c. Hs.{Lord Ernest Hives - Chair} c. BY/SD. BY.7/G.15.4.39. PHANTOM 111. PARIS DEMONSTRATION CAR. RE: BROKEN ROCKER SHAFT. As the result of examining the broken rocker shaft, I can say positively, and without any reservation, that the failure was simply due to an excessive impact on the front right hand road wheel. The evidence displayed in the form and type of fracture indicates that such a failure could only be produced by a single excessive impact on the wheel. The tensile strength of the actual shaft which was broken is 64 tons per square inch, the torsional moment to cause failure would be twelve and a quarter tons at one inch radius or an actual load of one and three quarter tons on the ball joint at the outer end of the pendulum lever. In round figures a load of 4000 lbs. or 1800 kilogrammes on the ball joint in question. We have had rocker shafts twisted as you point out, but not without an adequate reason in the form of a shock on the road wheel; in every case where the shaft has been found to be twisted in this country we have found the reason was the car had run into an obstruction. I have examined three or four shafts twisted up to 8º to 10º in accidents, but in no case had the shaft been found to be cracked nor would the shafts have been a source of danger if they had not been changed. In regard to this point of damage being produced without apparent adequate reason, we have changed quite a number of Bentley pendulum levers which have been found to be bent, during overhaul, and often it has taken a good deal of questioning before the owner could find a reason in the way of a 'bump'. Coming now to what may have been the actual cause of the failure of the shaft under discussion, I am of the opinion that it might be due to the right hand front wheel ploughing through the mound of loose earth. If the mound had been tightly packed the wheel would have ridden over it without serious shock, but with loose earth the wheel would | ||