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).
Fitting aluminium pistons for 40/50 and 20 HP chassis, addressing issues with seizing and knocking.
| Identifier | ExFiles\Box 77\3\ scan0273 | |
| Date | 4th October 1923 | |
| X.4224. To BY.{R.W. Bailey - Chief Engineer} c. to Hs.{Lord Ernest Hives - Chair} c. to Wor.{Arthur Wormald - General Works Manager} for SFT{Mr Swift}/AEM. EP{G. Eric Platford - Chief Quality Engineer}14/H4.10.23. RE. FITTING OF ALUMINIUM PISTONS. X.2748 40/50 AND 20 HP. CHASSIS. X.4224 We have been and still are experiencing a certain amount of trouble with the seizing or knocking of pistons. A considerable amount of attention has to be given in manufacture and during test, in order to ensure that satisfactory results are as far as possible being obtained and maintained. We have tried several sets with different methods of manufacture to see whether an improvement can be obtained in this respect, and we certainly have been able to obtain much more consistent and satisfactory results, both as regards manufacture and testing, by pistons which have been 'annealed' (Works report 350°C for 20 minutes and then allowed to cool off), and the pistons ground with the clearance and taper method of grinding and fitting as adopted by Springfield. The size of the skirt of the piston at right angles to the gudgeon pin is in this case increased .001", whereas the size of the piston across the gudgeon pin is the same as before, but the eccentric grinding is continued farther round the piston so as to leave only about ¼" of existing circular grinding at the top of the skirt at right angles to the gudgeon pin. We find that the ideal piston as regards bedding (which so far we have only been able to obtain by hand fitting) is one which shows after running that the load is more or less taken entirely at the point above referred to, which bedding is fairly hard and continues to the bottom of the skirt tapering outwards as arranged by the taper grinding. The bedding of the piston should then continue from this point towards the sides of the piston but the bedding as shown by the contact should get less pronounced until it gradually fades away and shows no bedding at all at the gudgeon pin ends of the piston. We find it is disastrous for the eccentric grinding to finish off abruptly, especially if this is not at a position somewhere in close proximity to the part of the skirt of the piston at right angles to the gudgeon pin. In fact the only real hard bedding marks should be at points at right angles to the gudgeon pin. Although the pistons we have recently obtained by the above method do not achieve the ideal bedding, they are certainly much better than what we have been getting, and certainly appear to be much more consistent in their results and the bedding contd:- | ||