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).
Stresses of tapered valve springs on the 'Phantom III' and recommending a switch to parallel springs for improved safety.
| Identifier | ExFiles\Box 96\2\ scan0135 | |
| Date | 4th September 1936 | |
| X 354 [Text crossed out] [Text crossed out] c. Hs.{Lord Ernest Hives - Chair} BY/Cgh.{W Clough}1/W.4.9.36. "Phantom III" Valve Springs. Further to BY.12/G.26.8.36, although the stresses by calculation do not appear to be excessive we consider that the actual stresses are very much higher owing to the fact that these springs have a large taper. As you are aware, we have tried tapered springs previously but they were always arranged with a relatively small amount of taper and although it has always been doubtful as to the advisability of using this type of valve spring, the taper of the "Phantom III" springs being relatively large, the coils at the small end are stressed considerably higher than what they appear to be by calculation, and evidently above the safe limit. Although the valve springs on the 25/30 H.P. and Bentley are tapered, the amount of taper is not so much as in the case of the "Phantom III", consequently the coils at the small end evidently do not reach the danger zone. We suggest that the taper of the springs is reduced, or better still, that the springs are made parallel in order that we may have a greater margin of safety and avoid having to maintain absolutely 100% quality material, workmanship and manufacture. BY/Cgh.{W Clough} | ||