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).
Tests on R. engine timing and camshafts, including diagrams comparing different timing settings.
| Identifier | Morton\M9\ img023 | |
| Date | 24th June 1931 | |
| The 20/25 benefits from 'R' engine inlet cams 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} Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}6/KT. 24.6.31. X7090. TIMING AND CAMSHAFTS. We have made some more tests with the 1140 R.{Sir Henry Royce} engine cam form camshaft. Hs.{Lord Ernest Hives - Chair}403 shews that we can pick up some of the low speed M.E.P. with an earlier timing. This once more confirms the fact that if a reasonable M.E.P. is required below 1000 R.P.M. it is useless to leave the inlet valve open after about 58° past B.D.C. (.020 tappet clearance.) Curve Hs.{Lord Ernest Hives - Chair}404 shews that the 1140 shaft is not so good as the 110° shaft even with exactly the same inlet valve timing, the reason being that to close the inlet valve early enough with this shaft the exhaust has to be opened far too early owing to the large angle between the cams. Again referring to Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}8/KT.17.6.31. we were wrong in assuming the timing on LeC.2918 to be with .020 tappet clearance whereas it is with .013 and therefore the inlet valve is not kept open as long as we thought, in fact it is almost the best timing with the 110° shaft, R.{Sir Henry Royce} cams with the inlet valve opened late (we think this is rather unnecessarily late) to avoid roaring and the exhaust valve closing earlier to avoid too much over lap presumably. .020 TAPPET CLEARANCE [Diagram 1] EX, IN, 9, 18, 50, 59 BEST TIMING R.{Sir Henry Royce} SHAFT [Diagram 2] EX, IN, 4, 9, 45, 50 RECOMMENDED TIMING ON LeC.2918 | ||