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).
Design and failure of Phantom III valve springs, with handwritten queries.
| Identifier | ExFiles\Box 96\2\ scan0138 | |
| Date | 17th September 1936 | |
| y354 Lt. Smith from E.{Mr Elliott - Chief Engineer} C. Wor.{Arthur Wormald - General Works Manager} Hs.{Lord Ernest Hives - Chair} By.{R.W. Bailey - Chief Engineer} Handwritten notes: ① If the springs surge what limit - and, is there to the stress range ② Surely, 30,000 to 81,000 is higher than Americans use. ③ How can we measure maximum coil separation when surging? Typed text: Phantom III Valve Springs Replying to your memo Sg.{Arthur F. Sidgreaves - MD}5/E.14.9.36, we are pursuing a renewed development with a view to producing a very low stressed valve spring which will run in carbon steel wire, but this is by no means the first time the matter has received our attention. We have from time to time made and tested springs of this type suitable for this type of wire, using large and heavy coils with plenty of wire, and alternatively triple springs of finer wire having low stress range and low maximum stress. These springs have broken up due to surging, and it is clear from the results obtained that there are factors other than spring design which influence the situation. My own view is that R.R. have always been so clever with cam design that they have obtained positive accelerations far in excess of what is generally used, and although this is good for power output it demands a spring with a high surge point, or in other words, a spring with the minimum of inertia in its free coils. Also apart from periodic effects these high positive accelerations do give the valve springs a frightful jab which loads up the end coils more on a high inertia spring. The balance between this requirement and the ability of the steel to withstand stress has resulted, in my opinion, in the type of spring we are using today giving the best results on test. To use a very low stressed spring may require a different cam form and some sacrifice of power output. The valve springs which were made for Rm.{William Robotham - Chief Engineer} in America to replace R.R. springs broken on the Bentley were identical in design with the Bentley springs. The only | ||