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 regarding the standardization of higher lift camshafts and stronger valve springs for the 25HP engine.
| Identifier | ExFiles\Box 102\5\ scan0104 | |
| Date | 24th November 1931 | |
| By.{R.W. Bailey - Chief Engineer} c.Hs.{Lord Ernest Hives - Chair} Y5090. BY/SS{S. Smith}4/N.24.11.31. Re: 25HP. Valve & Fittings - Valve Springs. x5060. Since it is intended to standardize the Higher Lift Camshaft and Stronger Valve Springs at an early date, the table below, and attached blueprints show the conditions under which these two features are being tested in france on 18-G-IV. The increased load is obtained by "pulling out" the standard valve spring approximately .500". It will be seen the new conditions involve several features which we suggest are unsuitable for production practice. These may be summarised as follows:- (1) The increased valve lift reduces the calculated clearance per coil from .026 to .015. Measuring an actual finished spring (enamelled) we find this clearance is reduced to .011. (2) With the maximum limits there is the danger of the top washer fouling the bottom washer when the valve is open. (3) The proposed valve spring Hs.{Lord Ernest Hives - Chair}451 is working at 100,000 lbs stress when the valve is open. Using existing parts we suggest it is possible to improve the coil clearance by lowering the bottom washer spring face .025. Since the 20/25 engine has always been a close job as regards valve washer and spring clearances, it may be considered necessary to lengthen the valve stem, raise the rocker shaft centre, and increase the length of the push rods by .075 - .100. An alternative is to modify the cylinder head by lowering the valve guide and bottom washer .050; which with the lowered spring face mentioned above, gives the total .075 required. Cont'd.{John DeLooze - Company Secretary} | ||