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).
On two design considerations for Bentley engine development, focusing on engine height and exhaust valve noise.
| Identifier | ExFiles\Box 82\4\ scan0155 | |
| Date | 17th September 1935 | |
| To E.{Mr Elliott - Chief Engineer} x200 Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}7/KW.17.9.35. Bentley Engine Unit Development. Two points on the design of this engine occur to me that we missed yesterday - (1) We want to keep the engine height down to the minimum. This means that we do not want to have to put anything on the block to enable us to remove the gudgeon pin from the piston as on the existing SpectreCodename for Phantom III. Therefore it occurs to us that the stroke bore ratio ought to be at least sufficiently square to ensure that we get a reasonable big end and that the connecting rod can be drawn through the bore. Advantage can of course be taken of the diagonal splitting of the big ends as on the Buick. (2) As we see the design at present, the exhaust valve is likely to be noisy. It is a big valve and we know of no suitable steel for it at present that has not a high co-efficient of expansion. It appears to us that an investigation has been made to see if the Halford tappet can be used on this valve in case of necessity. The objection to the Halford tappet on the present push rod Bentley was that it lowered the bouncing speed about 600 R.P.M. With a push rod engine we had not anything in reserve. There is no doubt that we did develop these to a considerable degree of reliability as proved by the fact that the Vulture has now run well over 12,000 miles fitted with a set and given the minimum of trouble. Since the total amount of valve clearance which these tappets will have to accommodate on an overhead valve engine will probably be less than .015", their movement can be limited so that the clatter when starting up is kept down to a minimum. Even on the Vulture we do not think that this was prohibitively objectionable. Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} | ||