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).
The pros and cons of a monobloc engine design with a cast iron crankcase and an aluminium head.
| Identifier | ExFiles\Box 134\2\ scan0105 | |
| Date | 16th February 1937 | |
| -2- (1) If we make it with a monobloc cast iron crankcase and cylinder, and aluminium head, it has the cast iron where it is most needed for rigidity, and the aluminium where it is most needed for heat conductivity - on our present standard Bentley engine this state of affairs is reversed. (2) It permits of the engine being made very short, and, at the same time, extremely good breathing can be obtained. (3) Material costs are less than the present Bentley. (4) It should simplify Foundry work enormously. (5) The all-aluminium engine of the J.III. type has to be spread out considerably to make it possible to get adequate water spaces in the cylinder head. The present P.III. is 3 1/2" longer than the Bentley, and it is generally conceded that it ought to be another 1 1/2" longer to make the cylinder head casting easy to produce; in other words, for equal Foundry technique this engine might be expected to be 4" to 5" shorter than P.III. construction. One of the biggest advantages of a short six cylinder engine is that the crankshaft master period lies out of the running range. Another is ridigity. (6) Apart from Foundry considerations, the monobloc construction should save appreciably in factory cost. The disadvantages of this engine would be that with the cast iron monobloc construction it would weigh 55 lbs. more than the present standard Bentley, and, of course, considerably more than the all-aluminium unit, some of which would be compensated by the reduced overall length of the motor-car. Briefly, we believe it is worth going into a design of this type of unit for a six cylinder engine, and getting it costed. Obviously, any recommendations other than that a complete unit should be built as an experimental piece of apparatus would be entirely premature as many troubles may manifest themselves on the multi-cylinder unit which were not apparent on the single cylinder unit. Basically, however, we consider that only by dividing the valving between the cylinder block and cylinder head can the optimum breathing be obtained continued | ||