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).
Effect of cam profiles on actual and theoretical valve bouncing speeds.
| Identifier | ExFiles\Box 17\6\ Scan258 | |
| Date | 21th June 1934 | |
| -3- Hs{Lord Ernest Hives - Chair}/Smth.23/KW.21.6.34. Effect of Cam Profile. Table II shows the actual valve riding speeds and the theoretical bouncing speeds for various springs and with different camshafts and cylinder heads. TABLE II. Head | Camshaft | Spring Initial Load & Rating | Actual Speed for Valve Riding | Theoretical Bounce Speed | Pt. at which Valve bounces | Ratio Actual sp.{Mr Spinney}/Theor. Spd. --- | --- | --- | --- | --- | --- | --- Vulture | E.{Mr Elliott - Chief Engineer} 82448 | 65/256 | 2650(EX) | 4540(EX) | 1st ch. over | 1.71 | | 85/256 | 3100(EX) | 5010(EX) | " | 1.62 | E.{Mr Elliott - Chief Engineer} 80070 | 65/256 | 3200(IN) (EX. unknown) | 4640(IN) | 1st ch. over | 1.45 | | 85/256 | 3300(EX) | 5060(EX) | " | 1.53 Standard | E.{Mr Elliott - Chief Engineer} 80070 | 65/170 | 3250(IN) | 4290(IN) | 1st ch. over | 1.32 | | 80/110 | 3300(IN) | 4310(IN) | nose | 1.31 | | 85/170 | 3400(IN) | 4770(IN) | nose | 1.40 These figures confirm the dependence of the trouble experienced with Cadillac Tappets on the tendency for the valve to bounce, but the discrepancy between the actual and theoretical valve bounce speeds and between the bounce speeds of different valves operated by the same camshaft indicates that the actual cam profile may depart considerably from the design. The difference in bounce speeds between valves actuated by the same camshaft may be of the order of 300 r.p.m. which indicates a discrepancy of some 2070 in the decelerations of the respective cams. Furthermore, two camshafts of the same piece number were tried in the engine and with the same results, which suggests that the trouble lies in differences between the contours of the master cams with which the master shafts are built up. | ||