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 memorandum discussing cam forms and valve timing for J.III and Peregrine engines, comparing theoretical values with test results and Alfa Romeo designs.
| Identifier | ExFiles\Box 13\2\ 02-page162 | |
| Date | 18th April 1932 | |
| -2- Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}2/A.18.4.32.contd. With regard to the cam form. We notice that the Alfa inlet valve is opening very rapidly, more so than ours between .013 and .020 lift. Cannot we copy this. Also can we get rid of some of our 'Toe' when we get the oil adjusted tappet. ('Toe' undesirable for burnt exhaust valves and 'roar' on inlet valve). EXHAUST CAM. The limiting point about this is how much over-lap we can have without spoiling the slow running. Alfa's have 80, P.II has 50. If we can cut the toe down we believe we can run with 30 to 100 without running into trouble. If we have got to close the exhaust valve at 80 A.T.C., we do not think we should open it later than 450 B.B.C. though Alfa's succeed in running opening 400 B.B.C. Supercharge may allow them to do this. On Sheet II therefore we give the recommended timing for J.III which we can reproduce experimentally by using two of the exhaust valve cams of the existing J.III shaft to Sch.1543. If we can have three cams for Peregrine with duration 222o, 230o and 235o we can reproduce the three timings shewn which should cover the range from a normal Peregrine to an ultra Bensport. If we are to get an indication as to how the valve gear will behave on Bensport we ought to run the 235o duration shaft on the first engine as this, be allowing a longer period for slowing up the valve, may allow us to use lighter valve springs than if we have a 22o inlet valve duration. Whilst on the subject of cam forms, we should like to point out again that we seem to get two or three degrees less duration in practice than we ought to get according to theory, probably due to deflection in the operating mechanism. Thus we have had two J.III's on test so far with the following results. Theoretical Valve opening duration at 1st J.III 2nd. J.III .020 CLCR. Crank Degrees. Unit. Unit. -------------------------------------------------------------------- Inlet 216o 210o 213o Exhaust 232o 225o 223o Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} | ||