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).
Modified 20 HP cylinder head with large diameter valves.
| Identifier | ExFiles\Box 106\5\ scan0008 | |
| Date | 30th May 1927 | |
| X5060 To E.{Mr Elliott - Chief Engineer} from Hs{Lord Ernest Hives - Chair}/ACL. Hs{Lord Ernest Hives - Chair}/ACL1/LG30.5.27. X5050 20 HP. CYLINDER HEAD WITH LARGE DIA: VALVES. In reply to E7/M26.5.27. Enclosed is a blue-print of the 20 HP. cylinder head made for use with larger valves. This was made from a standard casting by machining out the ports, both inlet and exhaust, to 1.400 dia. at the valve end. The ports at the manifold end remained the same as standard. The valves used were mushroom shape. It will be noticed that the valve seats are cut at 15°. At the time that this head was made 15° was the angle used on the standard engines. If this angle were increased to 45° - as with the present standard - we should not anticipate any appreciable difference in power. It will be remembered the seat angle was increased as it was found from tests that with the larger angle the valves were less liable to burn if run with very small tappet clearance. Hs{Lord Ernest Hives - Chair}/A.C.Lovsey. | ||