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).
Analysis of hydraulic systems versus solid rocker gear, comparing power, quietness and performance.
| Identifier | ExFiles\Box 96\2\ scan0233 | |
| Date | 1st June 1937 | |
| -3- In the present hydraulic system the valve is not free to do this owing to the friction imposed by the mechanism holding the rocker in close contact with the valve stems throughout the "cycle". We are not pessimistic over the solid rocker gear, but realise that we have not got to deteriorate from the present high standard of quietness which the hydraulic system gives. The result of the 15,000 miles' test will indicate the prospects of deleting the hydraulic system. POWER & SLOW RUNNING. As shown on the attached curve SP.{Mr Spinney}39A., the solid rocker gear in conjunction with the camshaft (Lec.5401) and the 4 port head is between 1 and 2 lbs per square inch M.E.P. down in comparison with the present production 6-port head with hydraulic tappets but crossing at 3,000 R.P.M. is 10 B.H.P. up at the high speeds. In comparison with the 4-port head with standard camshaft and hydraulic tappets, the solid rockers and camshaft (Lec.5401) with the 4-port head gives identical power at low speeds, is down by 2-3 lbs per square inch M.E.P. at the middle speeds and 15 B.H.P. down at maximum speeds. The reason for these results is that the solid rocker camshaft by reason of the low velocity quietening toes, the timing at the running clearance is of longer duration than the hydraulic mechanism and camshaft gives, and yet is a shorter duration camshaft on the main accelerations. The effect of the above is that the long toes are sufficient to detract from the low speed performance, and yet are of no help at high speeds, where, owing to the shorter duration of the main portions of the camshaft some power is lost. | ||