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).
The development and testing of inlet and exhaust valves, including different types, timing and bounce issues.
| Identifier | ExFiles\Box 134\2\ scan0139 | |
| Date | 23th August 1937 | |
| -4- (i) Inlet Valve. Two inlet valves have been tried, one a flat valve, the other of the tulip type. The former type, however, suffered two failures by cracking, and was abandoned in favour of the tulip valve, with which no trouble so far has been experienced. The valve timing was varied, and for the great majority of the tests, the inlet duration was set at 210° with a timing of I.O. 2° BTDC; I.C. 28° ABDC. The valve lift was maintained at .400", with the exception of the inclined valve head where it was reduced to .375", apparently without loss of performance. Some trouble was experienced at first due to valve bounce, but this was cured by fitting stronger springs to LeC.4185. It is obvious that loading would be fairly heavy on the valve gear due to rapid accelerations and heavy valves, and an attempt to reduce this by reducing the valve lift to .350" was made, this being done on No.1 head. A serious drop in power was experienced, however, and for the time being, the .350" lift was abandoned in favour of .400", which with the exception mentioned above was used throughout the development. When the inclined valve head came forward, however, it was decided to try some more valve timing tests with the object of increasing low speed power, and a timing of I.O TDC; I.C. 30° ABDC was ultimately selected, in conjunction with an exhaust valve timing of E.O. 35° BBDC; E.C. TDC. This timing, it will be noted gave no overlap, and is anticipated to be rather good for tick over and low speed power on a main engine. Valve bounce was experienced on this head at speeds as low as 3750 R.P.M., and ultimately this was traced to worn bottom tappets. On replacing these, a bounce speed of 4450 R.P.M. was observed. (ii) Exhaust Valve. When the unit was first designed it had an exhaust valve of 1.400" diameter. Open exhaust power was very much improved, however, by increasing the valve size to 1.500", and this is the size used for the great majority of the tests. | ||