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 the causes of piston knocks, identifying alignment and lubrication as the primary factors.
| Identifier | ExFiles\Box 35\2\ scan 110 | |
| Date | 29th August 1919 | |
| To R.{Sir Henry Royce} from EH. c to CJ. c. to BN.{W.O. Bentley / Mr Barrington} c. to E.{Mr Elliott - Chief Engineer} c. to BY.{R.W. Bailey - Chief Engineer} c. to Da.{Bernard Day - Chassis Design} EH4/LG29.8.19. 29th Aug. 1919 X. 2748. RE PISTON KNOCKS. We have been investigating to find the reason why on the majority of our car engines, we get some pistons which knock badly and others which do not knock at all. This of course has been our experience all along and has not come up since using aluminium pistons.. Usually there are one or two pistons which knock out the whole six. As a result of our investigations we find that the variation is due to the following causes:- 1. Alignment of pistons in cylinder. 2. Lubrication. Alignment. The alignment of the pistons is the chief cause of the variation. To test the alignment we are using a cylinder bore which has all the combustion chamber head machined aw-ay so that we can see and feel the top of the piston at any position of the stroke. We find, when we put this cylinder on to a piston which knocks, that the piston rocks about very freely and works truely in the bore. Under this condition we can easily produce a knock by hand by rocking the piston over. If we now pull that connecting rod so that the piston is out of line, we find that we cannot produce the knock by hand, neither will it knock when the engine is running. It is not necessary to tilt the piston so that it is binding | ||