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).
Experiments to reduce piston knocks using an oil-damped cylinder versus a spring.
| Identifier | ExFiles\Box 35\2\ scan 149 | |
| Date | 9th October 1919 | |
| X.2748. To R.{Sir Henry Royce} from EH. c. to CJ. c. to EN. c. to E.{Mr Elliott - Chief Engineer} c. to Da.{Bernard Day - Chassis Design} c. to EP.{G. Eric Platford - Chief Quality Engineer} c. to BY.{R.W. Bailey - Chief Engineer} RE PISTON KNOCKS. EH2/LC9.10.19. X.2748. X.3651. We have been experimenting with some standard pistons into which, on the non-pressure side, we have screwed a small cylinder. Into this cylinder we have fitted a piston which is 1.0" diameter. We have arranged an oil feed from the gudgeon pin to feed oil to the back of the piston. There is an annulus in the big end bearings so that we get the main oil pressure at this point. This is the scheme suggested by Mr. Royce; it promises to be good. We find that the success of this scheme is not so much due to the pressure of the oil keeping the piston against the side of the cylinder but to the fact that when this small cylinder is completely full of oil it is difficult for the piston to cross over quickly wnough to cause a knock because there is nowhere for the oil to leak out quickly enough for this to happen. The oil feed has simply got to be sufficient to replace any of the oil which is squeezed or leaks out. We find that if we use a spring instead of oil pressure we do not get as good result. With the spring fitted, it slightly reduces the knock at very small throttle openings but if we increase the load and open the throttle a little more, the knocks are still bad. We have tied with various springs up to 30 lbs. pressure. The strongest springs would not prevent the piston knocking if we applied a load such as one would get | ||