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 development issues concerning valves, valve springs, and cylinder head casting for engine 22-G-V.
| Identifier | ExFiles\Box 101\1\ scan0197 | |
| Date | 17th April 1936 | |
| X500a Sq. from E.{Mr Elliott - Chief Engineer} c. Wer. Hs.{Lord Ernest Hives - Chair} By.{R.W. Bailey - Chief Engineer} RHC.{R. H. Coverley - Production Engineer} Bft. De. R/GNR. (text is struck through) re 22-G-V.{VIENNA} With reference to the above, it will be remembered that this engine was first instructed with larger valves. These valves were of the same particular type that we had developed on the Bentley. It was then feared during the short time available for development that the large valves would not give good enough slow running, and it was decided to revert to the original 20/25 diameters. Unfortunately however when this was done we find that the old type of exhaust valve with a recess under the head was used instead of the Bentley type. This does not necessarily account for the breakage on test, but this particular shape of head does lengthen the amount of stem exposed to the heat, and the alteration we are making to 22-G-V immediately, and to production, is to use the Bentley shape of head with the larger Bentley radius between the stem and the head, which gives increased section at the point of breakage. The next point is the question of valve springs. The original instructions for 22-G-V were to use the Bentley strength of spring to EB.175. The actual springs with which 22-G-V was running were however to drawing E.60420, and this weaker spring it appears was fitted to reduce the valve bouncing speed and provide a margin of safety to prevent the engine reaching the major critical. It is felt however that the car may be run at such a speed as to cause incipient bouncing without the driver knowing it, and we therefore propose to revert to the original springs instructed, namely EB.175. We have now cut up the cylinder head and have found horizontal fins in the casting which may have interfered with the cooling of No.5. cylinder, although there is no blockage of the main flow horizontally underneath the fin. Core holes are provided in the design for inspecting for the presence of these fins, and are on the actual cylinder head on which failure occurred. | ||