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).
Letter regarding specifications and modifications for silent tappets on vehicle 28-EX.
| Identifier | ExFiles\Box 11\5\ 05-page146 | |
| Date | 10th August 1934 | |
| 27941 G.W. Hancock Esq., Hotel de France, Chateauroux, Indre, France. From Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}19/MJ.10.8.34. SILENT TAPPETS ON 28-EX. Attached is a specification of the silent tappets fitted to 28-EX. We found that it was possible to run with much finer plunger clearances on the mushroom valve tappets than with the ball valve tappets, the reason being that the latter hold the valves off their seats unless we have quite a large leakage factor. We have therefore fitted the poppet valves to your car. You also have cast iron eccentrics with a copper shaft. Here again this combination allows us to run with less clearance than the white metal lined eccentrics running on a steel shaft. We think this combination should be more or less trouble free as we have been doing a lot of running. We believe that owing to running with such fine tappet clearances the exhaust valves will tend to burn and for this reason have stellited numbers 2, 6, and 10 and fitted them with N.M.C. seats. At the end of your run you will be able to say whether this is necessary or not. We are sending you a complete set of spare silent tappet pieces which include ball valve plungers, steel eccentrics, and a hardened shaft. We only want you to use these if you have insuperable trouble with the others. Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} | ||