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).
Piston knocking issues and the practice of intentionally tilting pistons to resolve them.
| Identifier | ExFiles\Box 35\2\ scan 111 | |
| Date | 29th August 1919 | |
| H.H. Contd. STR. 15-4-19: C. 2554 2. EH4/LG29.8.19. against the cylinder walls, it is sufficient if it is tilted so that most of the clearance is taken up. We have now definately cured five or six bad knocks by tilting the piston out of line. We have also made pistons which were not knocking, knock badly by lining up the piston and rod. We have examined several engines and find that in all cases of distinct piston knocks the piston worked truely in the cylinder bore.. We realise it sounds bad to suggest adopting this as our practice to prevent knocks but we must not shut our eyes to the fact that the majority of pistons which are running are tilted more or less. There are such a number of parts which could effect the alignment that with very fine limits the errors would add up sufficiently to tilt the piston to overcome the knock. It means that with the tilted piston, when it reaches its maximum temperature and fills up the cylinder bore, the rod must be deflected slightly, but as we know many pistons are running like this; the rods do not appear to mind this treatment at all. We think this also explains why we find pistons which have a longer bearing surface have less tendency to knock because a less amount of tilt would be required before the clearance is taken up. For the same reason any decrease in the working clearnace is very beneficaal. We find if we adjust the alignment of the pistons we can fit up a car with the present aluminium pistons and the standard clearances which will not knock even when started up cold. Contd. | ||