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).
New taper valve springs and camshaft provisions to increase engine speed for the 20 HP model.
| Identifier | ExFiles\Box 17\6\ Scan057 | |
| Date | 10th November 1928 | |
| BY.{R.W. Bailey - Chief Engineer} from E.{Mr Elliott - Chief Engineer} c. to BJ. Hs.{Lord Ernest Hives - Chair} X7060 E3/M10.11.28. 20 HP. VALVE SPRINGS. Z.290 X.5060 X.7060 We send you herewith LeCs 2610/11. The former shews a new valve spring of increased load for putting up the speed at which the valves begin to jump. The increased speed is not more than approx. 5%. This spring is of the taper variety that we used in large numbers on the Silver Ghost. We have the idea that valve springs break at the top and mostly due to the heavy accelerations in the valve lift curve causing the coils to surge towards the top end, and putting up the stress range conditions locally. We therefore think the taper spring should be an improvement over the parallel one due to the decreased radius, and consequently lower stress in the upper coils. The coils should be wound to give constant clearance all the way up. Referring to LeC.2611 this gives information with respect to timing diagrams and a new exhaust valve lift curve for the 20 HP., using the present exhaust valve as an inlet. We have previously written in connection with this matter asking you to get out some cam forms on the lines of the SS.{S. Smith}, but as we had cause to investigate the point ourselves we looked into it and found it necessary to depart slightly from the original instructions, as R.{Sir Henry Royce} wished to use the old cam form if possible - LeC.1050. This cam form has a length of 56 divisions over the heavy accelerations, and because of this we have fixed the length of the new exhaust cam as 60 divisions over the heavy accelerations. We shall be glad if you will complete the information where required. The decelerations have been arranged with a 25% difference as per R's latest memo. With these new provisions for the camshaft there should be an increase in top engine speed of about 9%. E.{Mr Elliott - Chief Engineer} | ||