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).
Investigation into an engine knock, focusing on the rocker arm and valve spring assembly.
| Identifier | ExFiles\Box 66a\2\ scan0015 | |
| Date | 19th March 1926 guessed | |
| contd :- -2- thrust is on the valve stem. With this in view we packed up the rocker shaft and so bringing the line of contact of the pad to its correct position, lesson the forward thrust on the valve stem. We found however that although the rocker mechanism was quieter, it did not cure the knock. We found during these tests that we could not get the correct sweep of the pad until the rocker arm centre was raised .125". Examination of the standard rocker arms show that the circle of the pad is not quite correct to the drawing, but in view of the above tests, we have instructed a rocker arm which we believe will bring the line of contact correct and also gain the advantage of quietness that was noticed when the rocker shaft was packed up. Having proved that the rocker arm was not the cause of the knock, and by reason of applying only a light pressure on one side of the valve spring the knocking ceased, whereas when applied at the opposite side the knock increased. (The side in question varies with different valves). We then changed the valve spring knowing that previous troubles of this kind had been caused by the spring clicking on the spigot of the bottom washer. In this case however it did not cure it. We then changed the spring, top and bottom washers, and inserted a new felt washer. This, for a short time, cured the knock, but after racing the engine up, the knock returned. This led us to examine the fit of the bottom washer on the spigot of the valve guide, and we found that as a spigot, it was useless, the clearance being too great. This allows a valve spring that is not contd :- | ||