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 valve springs and camshaft provisions for the 20HP engine.
| Identifier | WestWitteringFiles\T\2July1928-December1928\ Scan200 | |
| Date | 10th November 1928 | |
| BY.{R.W. Bailey - Chief Engineer} [crossed out] FROM E.{Mr Elliott - Chief Engineer} C. to BY.{R.W. Bailey - Chief Engineer} [crossed out] HS.{Lord Ernest Hives - Chair} ORIGINAL [stamped] E3/M10.11.28. X290 [handwritten] X5060 [handwritten] 2610/11.X7060 [handwritten] 20HP. VALVE SPRINGS. 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 approximately 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 end 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 20HP., 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 '33', 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} | ||