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).
Modifications to the camshaft, rocker ratio, and valve train for Wraith III and Bentley III models.
| Identifier | ExFiles\Box 98\5\ scan0011 | |
| Date | 14th October 1937 | |
| -2- Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell}4/AP.14.10.37. (a) we wish to retain the reduced rocker ratio of Wraith III. to avoid the trouble hitherto experienced with the high ratio. As the top speed power is more necessary on Bentley than wraith the .400 valve lift should be retained. With this in view the cam lift will have to be increased from wraith at .275 to .310 for Bentley III. (b) The raised cam lift gives a bigger radius of scrubbing and therefore with the existing cone faced tappets unless a compromise is made between the angle of the inclined tappet and the cone angle of the tappet face, the scrubbing radius will exceed the radius of the tappet. Maintaining the existing 45' inclination of the tappet bore as wraith III, the cone angle of the tappet face to be fixed so that the 'scabbing' does not exceed the radius of the bottom tappet. (c) The fact of increasing the cam lift sharpens the tip of the cam profiles. Only by laying out the cam can the extent to which the tip radius is reduced by the increased lift, be seen. If the radius becomes too sharp, can the base circle be increased to retain the same radius at present on wraith III. camshaft.? Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell} | ||