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).
Analysis of piston pin wear and rattling issues, with a proposed design alteration to prevent distortion and knocking.
| Identifier | ExFiles\Box 81\2\ scan0085 | |
| Date | 10th December 1923 guessed | |
| Oy2-E-121023 -2- The attached sketch shows how we think this occurs, distortion being greatly exaggerated. A shows E-17765 compressed a little sideways against the aluminum. In case of (perhaps) an initial looser fit than usual, after a time this pin develops vertical slack by pounding away the metal at D which is not well placed to support the loads. In the case of B, the present type, this is not likely to occur because the aluminum is better placed to support the load. But whereas pin A is always marked lightly on the sides by the little end bush and does not wear the bush top and bottom, pin B always marks hard top and bottom at the ends as shown, and wears the bush rapidly. Also since pin B, like A is quite easy in the piston when hot the lockscrew gets rattled against the sides of its hole and shakes the threads loose, and we find two or three lockscrews in the crankcase of nearly every engine we overhaul on service, which we never found before. Proposed type C merely aims at making the pin stay round as the pre-war pins did, and gets rid of elusive knocks by avoiding the distortion which caused A to hammer loose. I think you should try this as it is a simple alteration scarcely affecting service and using E-17766 screw without alteration. Probably the reason that the pin does not knock if it stays round, even though expansion makes it loose in the piston, is because oil gets in between the pin and the aluminum. If not, all the engines which let the pin float in both rod and piston would knock and there are too many of them for this to be possible. Oy. M.{Mr Moon / Mr Moore} Olley MO/E | ||