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).
Modifications to the aluminium piston design to address piston knock and improve heat transfer.
| Identifier | ExFiles\Box 181\M11\ img089 | |
| Date | 31th October 1918 | |
| To EH. from R.{Sir Henry Royce} Copy to OJ. ORIGINAL 31st October, 1918. R1/G311018. [Stamp: 4 NOV 1918] X. 3402. X. 3400 [crossed out] RE ALUMINIUM PISTON FOR CAR. With reference to piston knocks, I think your suggestion is quite a reasonable one, but I fear we shall have to get over the trouble in a lighter and simpler form. For instance, we are anxious that the piston should carry its heat to the cylinder wall, so that the sleeve idea would have the disadvantage of being a heat insulator of the piston. My chief fear, however, is that it would either make the parts very thin, or the weight would be prohibitive. In the future there are two or three ways we can modify our present practice to get improvements. Firstly, a smaller diameter of piston, which will naturally follow for other reasons, a longer piston with a piston pin low down, and thirdly, the abandoning of the idea of the lower scraper ring, so that the oil can be all over the smooth surface of the trunk of the piston. We have every confidence that with these modifications* piston knocks will be a thing of the past. You will remember that our car engines are running particularly dry, that is, you never see any smoke at the exhaust. Secondly, although the Zephyr piston works cool, it does not seem to be one which carries the heat to the cylinder wall before reaching the little end, and the part which controls the piston. Moreover, we understand from Mr. Platford that pistons can be fitted so that knocks are not noticeable when the pistons are new, and we are (Contd.) [Handwritten note]* the overstatement of the decade! | ||