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 a case of engine bearing thump and piston knock, detailing the diagnosis and rectification process.
| Identifier | ExFiles\Box 131\2\ scan0067 | |
| Date | 30th September 1937 guessed | |
| - 5 - main and number 7 (see Chart B.117.JY chassis). During this week end a remarkable case of bearing thump has been dealt with. The owner's complaint was of an idling knock which disappeared as the engine warmed up. This was diagnosed as an ordinary case of piston knock, but the measurement of the cylinder bores, the pistons and the fit of the ring in the grooves, eliminated any possibility of any knock from this quarter. The gudgeon pins and bushes were in an 100% condition. The pistons were tested for cracks and were found O.K. A further examination of the engine disclosed the fact that main bearing sinkage was bad and all con. rod shells were loose. All the bearings were preloaded and refitted and on test no knock was apparent. I was present on the incoming test and at the moment the engine started its first run after rectification. In conclusion I would point out that it cannot be definitely stated that main bearing sinkage will in every case give audible warning when the amount of sinkage reaches the figure of .010" - even then the engine may only become rough and not necessarily shew even a drop in oil pressure. (See chart B.117.JY engine unit). Rm{William Robotham - Chief Engineer}/GWH.{George W. Hancock - Head Chateauroux} | ||