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 shorter duration cam form for the Bentley valve gear.
| Identifier | ExFiles\Box 88\4\ scan0195 | |
| Date | 16th December 1936 | |
| Swell. S dev 254 Rm.{William Robotham - Chief Engineer} c. Sg.{Arthur F. Sidgreaves - MD} Hs.{Lord Ernest Hives - Chair} By.{R.W. Bailey - Chief Engineer} Da.{Bernard Day - Chassis Design} Psn. Bentley Valve Gear. We are issuing LeC.5426 showing the cam form for a shorter duration timing, as proposed for trial with the head which has been developed from the Ulster results. It will be remembered that we proposed sacrificing some of the horse-power at the higher speed for the sake of improving the lower speed performance. The timing with this valve lift curve using the same form for inlet and exhaust gives a 5º earlier closing point for the inlet valve, which is a significant difference. The exhaust closes correspondingly later, but this as we know does not have so much effect. At the same time the overlap between the valves has been reduced by about 5º. This cam form has been provided with the longer duration toes required for the increased tappet clearances and on the closing side the toe has been made still longer and of the same dimensions as we are proposing for the new PhantomCodename for PHANTOM I III camshaft to suit non-hydraulic tappets and large tappet clearances. This shorter duration cam form requires a slightly stronger spring, and we have accordingly issued a spring with a slightly heavier gauge of wire, as shewn on LeC.5417 in which the average loading is increased and suitably proportioned to the force change curve. The present standard valve spring used in conjunction with the present standard camshaft is giving an exceptional result with regard to the bouncing speed. Our observations show that this bouncing speed is on the average 88.5% of the theoretical which is very much higher than that ordinarily obtained, particularly compared with the recently published results given for American engines. | ||