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 new type aluminium pistons for the X.2638 40/50 HP chassis, focusing on gudgeon pin issues.
| Identifier | ExFiles\Box 35\2\ scan 050 | |
| Date | 8th February 1919 | |
| W.H. 235a (500 T) (S.D. 408. 26-4-17.) Bm. 2/156/13. To R.{Sir Henry Royce} from EH. c. to E.{Mr Elliott - Chief Engineer} c. to BY.{R.W. Bailey - Chief Engineer} c. to Da.{Bernard Day - Chassis Design} X.3400A EH2/LG8.2.19. 8th February 1919. X.3400[PRE struck through] NEW TYPE ALUMINIUM PISTONS FOR X.2638. 40/50 HP CHASSIS We have fitted up a set of these pistons but we do not feel altogether satisfied with the system for holding the gudgeon pin. We found that if we carried out the instructions on the drawing, in rolling out the mild steel ring, we invariably damaged the bore for the gudgeon pin. The bore for the gudgeon pin has to be finished before the ring is put in, it takes then only the slightest burr to upset the fit. We found the best way we could fit these mild steel rings was to make them the diameter of the bottom of the recess then cur a slot out of them so that they would squeeze together small enough to pass into the recess. We made a tool to hold them squeezed together and found that they had sufficient spring to open out again when they were in the recess. We have on the aero engines been recommending that the gudgeon pin should be push fit and that the holes in the pistons should be broached. We carried out a 50 hour test to convince the A.I.D. that when the pins are push fit or .0005" slack or .001" slack, that they did not cause any harm after continuous running nor did they wear the pistons. The chief thing is, of course, to get a nice true smooth bore in the piston for the gudgeon pin. We found we got by far the best bore by broaching. The hand reamering of aluminium pistons, unless great skill is used, is not very satisfactory. | ||