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).
Experiments on camshafts for the Phantom II engine.
| Identifier | ExFiles\Box 13\2\ 02-page092 | |
| Date | 12th June 1931 | |
| To E.{Mr Elliott - Chief Engineer} From Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} c. to By.{R.W. Bailey - Chief Engineer} 870.90 Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}3/KT.12.6.31. P.II. CAMSHAFT EXPTS. We have conducted some experiments on camshafts on the P.II. The idea was that with the R.{Sir Henry Royce} engine shaft we have more duration and possibly slightly more lift than we require and could therefore, by varying the tappet clearance, get some useful results. Sheet I. shews the effect of varying the tappet clearance on each valve separately. It will be noted that the high speed power is almost unaffected by a decrease of 30° in its duration and .040 reduction in the valve lift. At .040 tappet clearance, on the other hand, the low speed M.E.P. is improved by 4 lbs/sq.in. The inlet valve is much more sensitive to any alteration at high speeds and also slightly more sensitive at low speeds as will be seen by the curves; combining the results of sheet I. Sheet II. shew that we get the best results with an inlet duration of 256 Crank Degrees and an exhaust of 236 Crank Degrees. LeC.2918 shews an Inlet duration of 244, at .013 clearance or 232 at .020, which we think will not drop more than 5 or 6 H.P. at the top and will give a good low speed M.E.P. If we alter the timing so that the inlet closes say 56° A.B.C. we can check if the inlet opening 12° before T.D.C. creates a roar but our previous roars from early opening inlets have not been nearly so bad as the roar from twin carbs. "ramming" and therefore we think that we can silence both together. Therefore we think that the Inlet on LeC.2918 is what we want as it has aero accelerations and a .480 lift and we presume the long toe will not spoil the result by increasing the effective duration unduly. With regard to the exhaust valve, you have given us 252 crank degrees duration and we only want 236 degrees for a good low speed torque. We should therefore like to make up a camshaft with the same cam for inlet as exhaust with the following timing (1). Even better might be an exhaust cam having (1) divisions less duration than the inlet giving a timing (2). (Diagram annotations) IO.12 EC.12 IC.56 EO.56 | ||