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).
Technical analysis of engine valve gear bounce speeds, with a table comparing theoretical speeds for various car models.
| Identifier | ExFiles\Box 17\6\ Scan298 | |
| Date | 18th July 1934 | |
| -3- The ratios in the last column do not indicate that flexure of the push rod in the case of the car engines is causing any undue lowering of the bouncing speed. This point has been checked in the case of Phantom, which gave the same bouncing speed with dural rods as with steel rods of 2 1/2 times the stiffness. The difficulty in estimating precisely the actual bouncing speed renders some of the ratios given in the table approximate only, but faults in the cam forms probably account for the large values found in some of the cases. Experience with Phantom has shown that there may be 200 or 300 r.p.m. difference between the bouncing speeds of the best and worst valves in a given engine. Owing to the effect of gas pressure, with equal weights of valve gear and with the same springs and cam forms, the inlet valves will bounce at a lower speed than the exhaust. Our experience indicates, however, that if the theoretical bounce speed (neglecting friction and gas pressure) of the inlet valve is more than 1% higher than that of the exhaust valve, then the exhaust valve will bounce first. Tappet Spring. The following table gives the theoretical bounce speeds for the tappet alone and for the rest of the valve gear alone, for various car engines. | | Tappet Alone | Rest of Gear Alone | |---|---|---| | Phantom II | 4700 | 4300 | | Bentley | 5400 | 5300 | | 20/25 HP. | 3200 | 4900 | | ||