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).
Analysis comparing the cost and performance of different valve springs, proposing a new universal spring made from Swedish wire.
| Identifier | ExFiles\Box 96\2\ scan0197 | |
| Date | 24th December 1936 | |
| -2- Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell}1/AP.24.12.36. Bentley springs made to Rm.{William Robotham - Chief Engineer}260., are particularly free from surge periods throughout the speed range as seen by the "Rotoscope" in comparison with our standard EB.175 Bentley springs. The latter have a period about 1500 R.P.M. and several above 4000 R.P.M. With regard to the comparative cost of "Swedish wire" with that of S/CV., the following are the prices which have been obtained per dozen springs - Standard EB.175 - 6.096s. mat. 2.111s. Labour = 8.207s. Swedish wire springs as made by the Tempered Spring Co. to EB.175. = 6.00 s. Swedish wire bought direct from Sweden by RR. would by comparison cost 1s.(approx) for material per one dozen.-EB.175 springs. Assuming the same labour cost in coiling and tempering this wire, as for our standard S/CV. at 2.111.s., then the total cost would be 3.111s. or a saving of 62%. Out of approximately 50 hours running at endurance speeds other than the chipping of the thin section ends in several of the special springs, we have had one failure with the "Swedish low carbon" wire. This occured on an RM.{William Robotham - Chief Engineer}53 spring on the second coil from the top. The RM.{William Robotham - Chief Engineer}53 spring is a copy of EB.175 but with .176 dia. wire instead of .160 wire, and the free length adjusted to give the same valve closed load. This type of spring was used in the T.T. race in S/CV. on account of its lower stress than EB.175 and improvement in not bouncing at 4500 R.P.M. In view of the encouraging results and prospective saving in cost, will you please detail and instruct for Swedish low carbon springs as follows. LeC.5417 which is intended to be a universal spring for 25/30, Bentley and Phantom as designed and alternatively with close coiling similar to RM.{William Robotham - Chief Engineer}260 with the exception of the top and bottom coil face which should be terminated at a reasonable section thickness. The springs to be produced by RR. from wire as bought direct from Sweden. Hm{Capt. W. Hallam - Head Repairs}/Swdl.{Len H. Swindell} | ||