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).
Valve seat materials, lead attack, and engine cooling methods for air and water-cooled engines.
| Identifier | ExFiles\Box 173\1\ img103 | |
| Date | 25th January 1934 | |
| -2- With regard to valve seat materials, air cooled engines are still using aluminium bronze inserts with heavy type sodium cooled valves, some of which have hollow heads of semi (not fully cooled) type. Latter have not been standardised on all engines although a certain number of Cyclone engines have been fitted with same. This type of valve is not entirely satisfactory owing to variation of material section, which has been proved at Works cannot be controlled effectively to the necessary fine limits, and also difficulty of inspecting makes it impossible to guarantee that material meets the growing requirements. The cylinders on the Conqueror are of butt-ended type with seats cut in roof of liners (see sketch). Therefore no alternative seat materials have been tried, but various valve material including stellite valves have been tried on both types of engines. Results, however, are so conflicting that while some consider stellite reduces lead attack, others think there is little improvement. The following is a summary of test results to date: 1. Sodium cooling apart from pre-ignition does not necessarily reduce lead attack. Hollow head valves have been used as already mentioned but not fully cooled. 2. They are not certain that hot valves are more immune from lead attack. 3. It is thought that lead attack is more pronounced under high power output conditions, but under lower powers corrosion causes valve sticking on stems. 4. Air cooled engines are considered to be slightly better than water cooled with regard to lead attack, but it is thought that if design would permit the introduction of two exhaust valves instead of one, tremendous improvement would result. | ||