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).
Table and analysis of valve spring loads against critical speeds for valve bounce.
| Identifier | ExFiles\Box 17\6\ Scan257 | |
| Date | 21th June 1934 | |
| -2- Hs{Lord Ernest Hives - Chair}/Smth.23/KW.21.6.34. TABLE I. Table Headers: Spring Loads, Valve at 1st ch. closed over pt., at max. lift, Rating, Speed for Valve riding, Calc. bounce speed, Ratio of Th.speed/ actual speed Table Data: Row 1: 50, 66.6, 130, 166, 2600, 3,920, 1.51 Row 2: 65, 90.6, 188, 256, 2650, 4,560, 1.72 Row 3: 70, 94.7, 189, 247, 2800, 4,660, 1.66 Row 4: 80, 96.6, 160, 166, 2900, 4,710, 1.62 Row 5: 85, 110.6, 209, 256, 3100, 5,050, 1.63 Row 6: 110, 128.5, 199, 186, 3250, 5,420, 1.67 Fig. 1 shows the critical speeds plotted against the valve spring loadings on a logarithmic scale. In the case of each of these springs the valves should commence to bounce at the first changeover point. That this is occurring in practice is evident from the curve. It is found, however, that with the Cadillac tappets the valves ride at some 60% of the theoretical bouncing speed (neglecting friction and gas pressure effects), whereas with the standard valve gear power does not fall off due to valve bounce until a speed of 3500 r.p.m. is reached, i.e., about 80% of the theoretical bouncing speed. Since the automatic tappet adjusters will take up the least amount of clearance occasioned by valve bounce, it is to be expected that trouble will arise from this source at speed lower than those at which the bounce is sufficiently violent to cause a fall in power with standard tappets. | ||