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).
Engine head modifications to resolve overheating and pre-ignition problems.
| Identifier | ExFiles\Box 106\5\ scan0166 | |
| Date | 31th July 1936 | |
| -2- In conjunction with the development work carried out for the T.T., we had considerable trouble due to overheating and pre-ignition with the head Ex.2094). On switching off at high speeds the engine would continue running for some time at almost the same speeds. The valve temperature in this condition was about 800°C. and by projecting a jet of water externally on to the valve head all this trouble was overcome. A modified head was produced to Ex.22594 whereby the water spacing in the head was continued further down behind the guide. The extent of this is that in the former head the base of the guide boss was 1.125" above the valve seat and in the modified head .625". Though we have no recorded figure of the valve temperature with the modified head, the temperature was appreciably lowered, the alteration in the deeper and cooler colour being visible to the naked eye. We have been enabled by the modification to increase the compression ratio from 8.5 to 9.5, and can run on the latter with normal B.P. Ethyl with only slight and passable pre-ignition. From these results we definitely recommend that the 25/30 HP. head be modified in the same manner for trial in lowering the valve temperature. Hs{Lord Ernest Hives - Chair}/L.H.Swindall. | ||