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).
Results of 10,000-mile tests on Halford and Cadillac silent tappets and proposing design improvements.
| Identifier | ExFiles\Box 17\6\ Scan308 | |
| Date | 6th September 1934 | |
| To E.{Mr Elliott - Chief Engineer} c. to WoR.{Arthur Wormald - General Works Manager} c. to By.{R.W. Bailey - Chief Engineer} c. to Wd.{Mr Wood/Mr Whitehead} x7060 Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}11/KW.6.9.34. Silent Tappets on Rolls-Royce Cars. Since writing Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}18/KW.27.7.34. we have had 10,000 miles tests in France on both the Halford tappet on the 20/25 and the Cadillac tappet on the 40/50. The results of the tests are all in favour of the Cadillac scheme. One serious disadvantage of the Halford scheme is the amount of oil which is released on top of the valves. In the 10,000 miles run this caused bad top overoiling. Another feature was that under the high oil temperature conditions encountered on the Continent the Halford tappet was not sufficiently quiet for Rolls-Royce standards. The stronger valve springs which have to be used with the Halford scheme are bound to react unfavourably upon the wear of the valve gear. We have therefore decided that in the case of the 20/25 and the Bentley where the layout of the engine is ideal for Cadillac tappets, we should go to this scheme. Since we expect the Bentley to remain in production for several years it would be well worth while carrying out the necessary design work, which will of course be directly applicable to the 20/25. Information we have so far obtained indicates that the following points should have attention - (1) We think that an eccentric ratio of 8 to 1 is about right. We prefer the eccentricity of the Phantom to that of the SpectreCodename for Phantom III as the latter has shown signs of sticking. We suggest as a compromise an eccentricity of .100. (2) We should like cast-iron eccentrics and E.Z.N. shafts coppered. These give the greatest immunity from eccentric jamming. | ||