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 valve spring performance, comparing double, single, and taper springs to address issues like bouncing and surging.
| Identifier | ExFiles\Box 56\2\ Scan064 | |
| Date | 20th February 1929 | |
| - R.{Sir Henry Royce} FROM E.{Mr Elliott - Chief Engineer} [R.{Sir Henry Royce} is crossed out] SECRET. C. to SS.{S. Smith} RG.{Mr Rowledge} HS.{Lord Ernest Hives - Chair} BY.{R.W. Bailey - Chief Engineer} [HS.{Lord Ernest Hives - Chair} BY.{R.W. Bailey - Chief Engineer} is crossed out] VALVE SPRINGS. X290 [Handwritten, and also handwritten and crossed out below 'VALVE SPRINGS'] The double valve spring originally instructed for SS.{S. Smith} had a bouncing speed of 2700 compared with 2900 for the standard Phantom spring E70442., in spite of, as we find, its average pressure being about 2.5 lbs. more. These double springs were instrumental also in causing the valve gear to emit a "loud high pitched clicking noise" at 1250 RPM. which could be heard on the road, particularly on the over-run, and which was consistent on a number of engines. The first engines were therefore run with standard single valve springs E70442. [Handwritten note: Phantom] Subsequently it appears that single springs of heavier gauge and load were fitted by Derby and used on the 10,000 miles test. These probably put the bouncing speed up to 3200. When we came to look into the question of designing a SS.{S. Smith} taper spring of the 20HP. pattern it was somewhat puzzling to know in which direction to proceed, as the original double springs which had proved a failure had an exceptionally good figure of merit-e.g. 1.2., and this latest spring used by Derby was only .95 (FOM = 90,000 / Max. Stress range. ) Nevertheless we proceeded on the principle that any parallel spring can be improved by making it taper and we calculated some springs of about the same loading but somewhat improved figure of merit of about 1.05. Needless to say we were not satisfied and before putting these springs forward for your inspection we entered into general investigation of this peculiar state of affairs. Naturally the question of surging and periodic vibration was the phenomenon to be considered as we have observed that any spring we have put forward that has had a particularly good figure of merit for stress has always been noticeably bad for surging; moreover we have never succeeded in consistently demonstrating that springs so designed for low stress were an improvement as regards standing up. We first calculated the periodicities of a number of different springs of known performance as follows: (1) | ||