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).
Camshaft recommendation for the Bentley III unit, comparing it with the standard camshaft.
| Identifier | ExFiles\Box 98\5\ scan0010 | |
| Date | 14th October 1937 | |
| 407 To Da.{Bernard Day - Chassis Design} from Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell} 200 B Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell}4/AP.14.10.37. BENTLEY III. CAMSHAFT. Regarding a camshaft for the above unit we recommend that a shaft in accordance with the valve lift curve LeC.5426 be used. This is representative of the best that can be done combining the following features. (a) Low Velocity closing toes up to a lift of .020 to give quiet operation of valve gear on par with Wraith. (b) Minimum overlap in order to obtain slow running, by use of higher velocity opening toes than closing toes. (c) Shorter duration under main accelerations of the valve lift curve giving less overlap for improved slow running and Inlet close and Exhaust open positions nearer to bottom dead centre for improved M.E.P. at the low and middle speeds. The above remarks are made in comparison with the existing standard Bentley camshaft, likewise the following. As tested on a standard 4¼ litre Bentley, the recommended LeC.5426 camshaft gives the same max. power at the same speed, but begins to fall short above 4000 R.P.M., whereas the M.E.P. is 5 lbs/sq.in. or 4½% up at the low speeds. The attached curve shows the actual power comparisons of the two shafts. At .012 tappet clearance (LeC.5426) shaft has appreciably quieter valve operation and the slow running a slight improvement in comparison with the standard camshaft with tappet clearances of .006. From these results it will be seen therefore that it is difficult to conceive a shaft that would give better all round results. Regarding the application of this LeC.5426 to Bentley III. which has flat bottom tappets, there are several points requiring explanation and are as follows:- continued | ||