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 valve material issues, specifically lead attack and stretching, on the 20/25 model.
| Identifier | ExFiles\Box 101\4\ scan0091 | |
| Date | 6th September 1935 | |
| G.W. Hancock Esq., Hotel de France, Chateauroux, Indre, France. X500a Hs{Lord Ernest Hives - Chair}/Rn.{Mr Robinson}9/KW.6.9.35. Exhaust Valves on the 20/25. We wired you to-day as follows :- "ONE AND FOUR EXHAUST VALVES SILICHROME ANTICIPATE THESE WILL FAIL WITH LEAD. SHOULD LIKE REPORT ON CONDITION OF OTHER VALVES. ROBOTHAM." One of the main things we wanted to find out on 21-G-IV was whether the stellited silichrome steel would be a satisfactory valve material. You will recollect that the objection to KE-965 is that it has a high expansion, which means that on the Bentley we have to run with a large exhaust valve clearance which causes noisy valve gear. The objection to Silichrome is that it is very susceptible to lead attack and when the seat of the valve gets scaled by the lead it overheats and the head drops off. The ideal therefore appeared to us to be stellited silichrome valves, as we do not expect the heads to drop off if the seats keep in good condition. Another point is that when we ran Firth's Crown on the 20/25 a long time ago we found that they stretched. KE-965 is much the same material as Firth's Crown. We concluded that they stretched on the 20/25 and not on the Bentley because of the slow closing toe on the camshaft allowing the valves to get hotter than the short toe Bentley camshaft. Briefly, therefore, the information we should like on 21-G-IV is :- (1) Are the KE-965 valves in Nos. 3 & 6 cylinders showing any signs of stretching ? (2) Is the exhaust valve which failed in either cylinder 1 or 4 ? If so, both these exhaust valves should be replaced. | ||