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 knock, its causes, potential cures by misaligning the connecting rod, and the suggestion to educate drivers.
| Identifier | ExFiles\Box 35\2\ scan 122 | |
| Date | 5th September 1919 | |
| Contd. -3- R3/G5.9.19. of the small end of the connecting rod. So that it would appear that in the past we have been throwing away the most perfectly made pistons and retaining the pistons and connecting rods which give us some slight want of alignment. As our system of manufacturing pistons and connect- ing rods produces generally excellent parts, we are naturally the ones who would be troubled with the greatest percentage of knock- ing pistons. It would therefore be quite easy for the Works to turn out cars with either cast iron or aluminium pistons which do not knock while warming up or afterwards, by throwing the con- necting rod's 'little end' slightly out of square. As far as can be detected the amount of this error required to stop a piston knock does absolutely no practical harm. I cannot, however, agree to such a practice, but it opens our eyes to the fact that we have been throwing away in the past, our most perfectly made pistons, and hunting for a pair of pistons and rods which are imperfect. As soon as the fact becomes known that a piston knock can be cured by a slight set near the little end of the rod, we shall probably hear no more of piston knocks, but I cannot cir- culate it or agree to it as a legitimate cure for the slight im- perfection of an engine which has a perceptible sound during the first few minutes of warming up. It would be nearly as bad as agreeing to the fitting of very tight cast iron pistons which are liable to sieze. What we really want is for the Sales Dept. to educate the drivers that there is absolutely no harm in the slight piston Contd. | ||