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).
Comparison of the turning evenness between a 12-cylinder Packard camshaft and a standard 6-cylinder camshaft.
| Identifier | ExFiles\Box 35\3\ scan 012 | |
| Date | 20th April 1920 | |
| X.2464 To R.{Sir Henry Royce} from Hs.{Lord Ernest Hives - Chair} c. to CJ. c. to Bn.{W.O. Bentley / Mr Barrington} c. to E.{Mr Elliott - Chief Engineer} c. to Da.{Bernard Day - Chassis Design} Hs{Lord Ernest Hives - Chair}3/LG20.4.20. X.435. CAMSHAFTS. X.3423. ----- --------- X.2764. ----- We have been comparing the evenness of turning the 12-cylinder Packard camshaft and our standard 6-cylinder car camshaft. There is a very big difference in the evenness of turning when they are turned over slowly by hand. With the 6-cylinder camshaft, six times in the revolution of the camshaft it runs forward for a period of approximately 12°. This occurs when the valves which are open, just across over at the top of the cam. The camshaft at that point runs forward until the spring pressures of the valves opening and the valves closing balance. With the 12-cylinder Packard camshaft compared in a similar way, it turns very much more evenly. There is no sign of it over-running, although one can feel variations in the load required to turn it. Does not the 12-cylinder camshaft gain one advantage due to the fact that the weaker valve springs can be used owing to the small diameter valves of the 12-cylinder? We have tried our present car engine with weaker valve springs and find that the the camshaft turns less unevenly. When the engine is running we find that it requires less braking on the camshaft to silence it when we used the weaker valve springs than it does when we use the stronger valve springs. We have made the following experiments on one of the standard car engines:- Contd. | ||