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 masked inlet valve timings and camshaft configurations to improve engine idling performance.
| Identifier | ExFiles\Box 158\5\ scan0100 | |
| Date | 13th November 1940 | |
| 1360 To Rm.{William Robotham - Chief Engineer} c. to Rm{William Robotham - Chief Engineer}/CTS.{C. Trot Salt - Carburation} c. to Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden} Jnr.{Charles L. Jenner}1/JH.13.11.40. MASKED INLET VALVE AND IDLING OF THE HIGH POWER HEAD. Rm.{William Robotham - Chief Engineer}1/ML.27.10.40. Before seeing how much the masking of the inlet valve is worth, it was necessary to analyse the inlet valve timings under running conditions, comparing the good slow runner with the poor slow runner. They are :- | Ex.33975 | 113¼° between the cams. | .010 Inlet tappet clearance. | .012 Exhaust tappet clearance (hot) | Slow running 270 r.p.m. | |---|---|---|---|---| | EB.4512 | 109½° between the cams. | .010 Inlet tappet clearance. | .015 Exhaust tappet clearance. | Slow running 340 r.p.m. | When these actual running timings are compared on the usual circular diagram the amount of overlap between the opening of the inlet valve and the closing of the exhaust valve is almost the same, being 32½° for the good camshaft and 30° for the poor one. This amount obviously does not explain the difference in idling. By plotting the closing toe of the exhaust valve and the opening toe of the inlet valve we can detect why the 113° camshaft is the better. It is because at T.D.C. the exhaust valve is only open half the amount approximately, compared with the 109° shaft. This has been shown on PL.400. The proposed masked valve which is recessed to the extent of .015 and having an annular space of .005 at the valve head has been compared with the standard valve for areas for the first part of the lift, both areas are the same for the first 17° movement of the crankshaft after taking up the tappet clearance, then the masking takes effect, but only exists for a duration of 4°. Since this happens at 7° past T.D.C., we cannot see that it would improve the idling. Cont'd.{John DeLooze - Company Secretary} | ||