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 valve gear design, back pressure issues, and cylinder head development.
| Identifier | ExFiles\Box 134\2\ scan0147 | |
| Date | 23th August 1937 | |
| -9- (viii) Valve Gear. The valve gear, looked at from the point of view of the bottom tappet appears to be rather heavy. Loadings of the valve spring are up to Wraith figures, viz., 32.6 lbs seat load and 130 lbs valve open load, and in addition bottom tappet springs have to be employed. A lightened valve gear in duralumin has been asked for, and will be tested on the single cylinder unit. Modified inlet rockers have also been requested giving a reduced lift of .350", and it has also been decided to try smaller valves in conjunction with venturi ports, this it being hoped giving the same power with a lighter and smaller valve. A consideration of the exhaust valve loading shows that gas load, coupled with a large valve and high lift, are leading to very rapid tappet wear. It has been suggested, therefore, that a scheme be got out to try the bottom tappet acting directly on the valve stem. This will eliminate several moving parts, and reduce loading and tappet wear. It will, at the same time, however, reduce valve lift, which may seriously affect power output, though this is not anticipated. This feature can be tested on the single cylinder unit. (ix) Back Pressure. It has been found that the power loss at high back pressures is directly influenced by exhaust valve timing, especially at top speeds. Further tests are, therefore, to be made to investigate this matter thoroughly. As will be seen from the above, development has reached a stage when a cylinder head and block can be designed with a fair degree of confidence. Modification to the single cylinder head will no doubt have to be made to adapt it to a main engine, and this will involve a final test of the head of the type employed. Provided, however, that the points noted above are adhered to, no serious snags are anticipated. Rm{William Robotham - Chief Engineer}/Ed.{J. L. Edwards} | ||