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).
Carbon steel spring failures, comparing American and English methods, and detailing stress figures for modified Phantom III valve springs.
| Identifier | ExFiles\Box 96\2\ scan0139 | |
| Date | 10th September 1936 guessed | |
| (sheet 2) difference lay in the material which was of carbon steel but which was free from the decarburisation defects present in the English variety as Hl's examination showed. It would appear that the Americans have better methods of producing these carbon steel springs than are available over here. The cause of the R.R. springs failing in this case is still a mystery and no explanation was forthcoming from the examination of the broken pieces by our Lab. Referring now to the Phantom III valve springs as originally designed, these worked to very low stresses. They have however since been twice increased in loading by the Experimental department to deal with a phenomenon of this mechanism picking up incipient bounce which showed on the automatically adjustable valve tappet gear. Again this may be associated with our high positive cams and flexibility in the valve gear. The corrected stress figures for the outer springs are as follows:- | | Valve closed. | Valve open. | Max. choc stress. | | :--- | :---: | :---: | :---: | | P.III springs LeC. 4124 as designed. | 21,000 | 64,000 | 72,000 | | As increased 1st time. E.87498. On production now. | 30,500 | 73,500 | 81,500 | | As increased 2nd time E.87952 and 1st instructed on production. | 37,000 | 80,000 | 87,500 | These Phantom III springs are of the double variety and there is an inner spring of similar taper with somewhat higher stresses than the outer of LeC.4124, which has never been altered, and has never given any trouble. | ||