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).
Experiments to cure piston knock using oil pressure fed to the gudgeon pin and pistons.
| Identifier | ExFiles\Box 48\1\ Scan110 | |
| Date | 30th September 1919 | |
| -4- find, however, that it is necessary to have a pressure of oil conducted to an annular groove on the piston before it is effective. For our experiments we have made use of a connecting rod which had an annular groove in the big end bearing so that we could obtain the full pressure of oil up to the gudgeon pin. The gudgeon pin was drilled and from there we led the oil to an annular groove round the pistons. The pistons we used for this experiment were standard which had been ground smaller so that the clearances were .011" and .007". These pistons knocked badly under ordinary conditions. They also knocked badly even if the extra oil was kept on the whole time or if we allowed the oil to only leak through the gudgeon pin. With the oil pressure on, the pistons knocked at the first instant of starting up but as soon as the oil pressure had built up, the knock disappeared entirely although the engine was still quite cold. We repeated this test several times and got consistent results. This is the only way so far that we have been able to definitely cure bad piston knocks by means of oil. having the extra oil on the whole time does not have the desired effect. As one would imagine, when we use this pressure of oil, we get into trouble with oil working past the piston. We are endeavouring to overcome this; at Bn{W.O. Bentley / Mr Barrington}'s suggestion we are using two scraper rings in series. The experiments we are now concentrating on as regards piston knocks are pistons which are split on the non-pressure side and the piston which has an oil supply fed by pressure. EH. | ||