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).
The design of 40/50 HP pistons to reduce knocking and improve oil scraping.
| Identifier | Morton\M11\ img201 | |
| Date | 27th August 1919 | |
| To EH. from E.{Mr Elliott - Chief Engineer} Copy to CJ. " " BN.{W.O. Bentley / Mr Barrington} " " EFC. ORIGINAL. E2/G26/8/19. RE 40/50 H.P. PISTONS. X.2478 Referring to your report in which you say that the set of pistons on 49 GB which did not knock, had the rings high up on the piston, Mr. Royce wishes me to point out that the object in dropping the rings was to get over the tendency of the piston to scrape oil upwards, and to provide in effect, a longer piston, which by reason of its increased effective length, would have less tendency to knock. These two aims can only be realised if you succeed in making the piston fit with relatively small clearance immediately above the piston rings, which was part of the alteration that accompanied dropping the postion of the rings. Would you kindly say what clearance you are using at this point. When examining the first set of pistons with the higher rings their tendency to lift oil should be compared with the later type. E.{Mr Elliott - Chief Engineer} RECEIVED 27 AUG 1919 | ||