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 design considerations including supercharging, cylinder heads, and valve configurations.
| Identifier | ExFiles\Box 133\2\ scan0106 | |
| Date | 19th November 1934 | |
| -3- We have a certain apprehension about the exhaust valve in the high power head, more particularly if we should supercharge it. The question of whether a detachable head should be used with an overhead camshaft drive or not is interesting. We believe that there will definitely be no need for a detachable head from the point of view of the valves requiring attention. Decarbonisation is open to argument. With the excellence of modern oil control, and thermostatically controlled hot spots preventing an over-rich mixture being used for starting, this is becoming a less frequent maintenance job. If we do use a detachable head we are beginning to find ourselves limited on the size of piston which we can use, which is not a very satisfactory position. Generally speaking, we believe we are getting to a state where the piston rings, valves and decarbonisation will only be required at about 20,000 miles and this will be a major service job, so that lifting the block will not be considered to be unreasonable. It must be remembered that there are at the present moment quite a number of cheap cars running about with non-detachable heads; these include the Hornet and the new Daimler Lanchester range, and these will be serviced by far less competent people than the average Rolls-Royce car. With regard to the loss of rigidity when the cylinder block and crankcase are not made as a monoblock casting, we agree we do not know what this will be worth, but experiments can be made on the subject. The one disadvantage we see of a monoblock cylinder head and block is that it will have to be made in aluminium to get the power weight ratio we require, and the necessity for inserts may reduce the valve area available. This is one of the reasons why we have kept to the C.I. head on the Bentley. If we have comparisons of overhead valve inlet - side valve exhaust, two vertical overhead valves, one vertical and one inclined overhead valve, four inclined overhead valves and a sleeve unit, we shall be in a strong position for knowing which way to move in future engine design. | ||