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).
Secret memorandum on the valve lift and valve springs for the EAC engine, with comparisons to other engines.
| Identifier | ExFiles\Box 72\1\ scan0178 | |
| Date | 18th January 1924 | |
| To R.{Sir Henry Royce} from E.{Mr Elliott - Chief Engineer} c. to CJ. HS.{Lord Ernest Hives - Chair} RG.{Mr Rowledge} S E C R E T. RE. E.A.C. VALVE LIFT AND VALVE SPRINGS. X. 9060 VALVE LIFT. The valve lift with which the EAC. engine is at present running is slightly less than pro rata Goshawk reckoned on the valve port diameter, but is a little more than Hawk and Falcon, these latter being .46" and EAC. .49". The effective EAC. valve port opening however is less than Hawk and Falcon due to the use of 45° valve seats as against 30° shewn below, and we were balanced between getting the valve lift too high, and getting the power too low :- See original for sketch. The effective EAC. port area between the valve head and the seat is just equal to the area of the 1.75 dia. port less the valve stem, and therefore reckoning in the effect of the valve lift is none too large for the valve. The effect of the 45° could be partly countered by making the seatings narrower than we have hitherto used in car practice. The above are the considerations on which the EAC. valve lift was based. Nevertheless we afterwards suggested and received your assent to producing some lower lift cams and expect to calculate these next week. We propose to make these .4" lift which is the same as present 40/50 HP. VALVE SPRINGS. The mean stress in the EAC. valve spring is identical with the mean stress in the largest convolution of the present 40/80 spring, but the stress range is 18% more. It was on this account that the lower lift was desired. By reducing the valve lift to .400" or to be exact .410", the stress range would become the same as 40/50. We propose to do this but also to keep the mean stress and load unaltered so that the valves will then jump at a higher speed than 2500 (74 m.p.h.) e.g. about 2730 (81 m.p.h.) and also the present relation between the valve and valve tappet springs will be retained. We think the engine ought to be able to run up to this speed and that it will most probably do so without touching a period. We are asking Derby to send us models of the moving parts of the valve gear which we have never yet seen, to make contd:- | ||