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).
Failures of piston pin locking screws (E-20096) and a proposal for a redesigned version.
| Identifier | ExFiles\Box 10\1\ 01-page59 | |
| Date | 31th July 1923 | |
| Oy1-E-75123 [Handwritten notes:] Record despatch in digest Ref'd to G.E. others for S. [Circled:] R Vace File ID RI/M24823 Dealt Seen July 31, 1923. Mr. Claude Johnson, Rolls-Royce, Limited, London, England. (Copy for attention of Mr. Royce r.{Sir Henry Royce} Platford} Mr. Hives ) X [Handwritten] Dear Sir: Re Piston pin and locking screws We have had several cases on Test of the piston pin lockscrews E-20096 having broken off where the screw passes through the pin. A broken sample is enclosed, from which it can be seen that a perfect Stepton fatigue break is obtained. [Red stamp over text:] COPY In all these cases we know that the little end fit was on the tight side, but the bush had not seized. Since the lockscrew expands the ends of the pin and makes the fit tighter between the pin and the little end bush, occasional tight little end fits are likely to occur, and we therefore feel that there is a real danger of these lockscrews breaking after leaving our hands. At the same time we find that slack develops faster between the little-end bush and pin than it did with the old type pins E-17785 because the bush bears against the pin on two small patches top and bottom at each end of the pin, where it is distorted oval by the lockscrew. We ran 24,000 miles on a set of old type piston pins with a wear of less than one thousandth, whereas the new type pins developed 2 1/2 thousandths slack and produced a very bad engine rattle on the retard, in 10,000 miles. We do not suggest to revert to the old type pin because we find that these wear the holes in the piston bosses oval. Our proposal is shown on print E-20096 enclosed, which shows the lockscrew threaded 5/16 diameter, and the end left 1/4" diameter | ||