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 Phantom piston knocks caused by cylinder distortion, with proposed solutions.
| Identifier | ExFiles\Box 66\1\ scan0142 | |
| Date | 11th July 1927 | |
| F.C.S To Hs.{Lord Ernest Hives - Chair} from Mr. _____ RECEIVED JUL 11 1927 X8040 Mxl/T11.7.27. Phantom Piston Knocks. The result of our recent investigation of the above with regard to cylinder distortion is as follows:- We find that normal pulling down of a cylinder head results in a distortion of the cylinder bore at the lower end, of an average difference in diameter of about .005, this on the latest long type cylinders, which are less prone to the trouble as they are relatively stiffer than the earlier types. The original Phantom cylinder under the same conditions shews double this amount. The distortion is most marked on Nos. 2 and 5 cylinders i.e. the centre cylinder of each block, and it appears that about 40% of the distortion remains even after the cylinder head is released. We have had very satisfactory results from fitting 4 stiffening plates in the water jacket cover aperture. With these plates fitted there is no sign of the 2 and 5 knock at any engine speed even when "listening in". We have however had to modify the pistons to suit the new condition. We asked the Works on July 1st. to discontinue the stretching of Phantom pistons and to do only such fitting as is carried out on the 20-HP piston which consists of blending in the sharp lines which are left by the grinding operation. We are of the opinion that the final grinding operation should be carried out after completing the split, and for this purpose propose that .005 be left on. We would like to have a piston which does not require any hand filing at all, and no doubt we shall be able to do this in the near future. In an endeavour to attain this we have developed a set of pistons in a set of reinforced cylinders, which when pulled down on a crankcase were practically free from distortion. This chassis has been given a good test both on dynamometer and road, and the engine has no piston knocks, either starting from cold, 2 and 5, or rippling knocks, which latter are the result of local tightness. contd:- | ||