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).
Exhaust and inlet valve failures, material changes, and subsequent valve spring tests.
| Identifier | ExFiles\Box 82\4\ scan0380 | |
| Date | 1st October 1936 | |
| -3- Hs{Lord Ernest Hives - Chair}/CTS.{C. Trot Salt - Carburation}16/KW.1.10.36. As mentioned in the above report, larger exhaust valves were tested, and the only ones available had had considerable previous running. There was insufficient time to have new ones made, but the test proved useless as a valve head came off after 7 hours' endurance. At the same period, 2 inlet valves collapsed, breaking off at the groove of the 'safety ring' device for preventing the valves from dropping into the cylinders. In the case of the inlet valves, it was decided to change the material from Silchrome to KE-965. These failed after 16 hours high speed running (including 10 hours endurance), small pieces breaking away from the seats. It was later learned that these valves had been produced from forgings originally intended for aero valves. It was be appreciated therefore that it would only be necessary to use the centre core of these forgings to produce the valves in question. The same characteristic of failure had been experienced in Aero development, where the cause had been gone into more fully. They found that when using KE-965 for inlet valves, the failures could be traced to the wrong type of grain-flow, brought about in forging. With the abandoning of the "le Mans" 24 hours race, the necessity for long life in high speed endurance for the valves was not so important. In view of the exhaust valve failures, however, valve spring tests were carried out to determine the lightest seat loading that could be used, without allowing valve bounce. The following values were obtained - 20/25 springs - bounce speed = 3700 R.P.M. Standard Bentley springs - " " = 4300 R.P.M. Rm.{William Robotham - Chief Engineer}55 springs - " " = 4500/4600 " | ||