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).
Piston knocks, detailing the theory that a flexible piston skirt is required for silent operation across various temperatures.
| Identifier | WestWitteringFiles\N\2October1925-December1925\ Scan21 | |
| Date | 12th June 1925 | |
| R.R. 493A (50 H) (D.D. 31, 12-6-25) J.H.D. EXPERIMENTAL REPORT. Expl. No. REFs//ACL/LG1C.10.25. To R.{Sir Henry Royce} from Hs.{Lord Ernest Hives - Chair} c. to CJ. BJ. c. to RG.{Mr Rowledge} E.{Mr Elliott - Chief Engineer} c. to DA.{Bernard Day - Chassis Design} BY.{R.W. Bailey - Chief Engineer} c. to Wor.{Arthur Wormald - General Works Manager} PISTON KNOCKS - E.A.C. Continuing our experiments on pistons the results obtained up to the present time all tend to confirm our previous theory, i.e., that the type of piston required to operate silently over a wide range of temperature conditions is one having a flexible skirt which will accommodate itself evenly to the cyl. bore as it itself expands. By accommodating itself to the bore, we mean with regard to an even bedding surface, fore and aft, so that a good oil film is preserved. No particular difficulty seems to present itself in obtaining this condition on the pressure side but on the split side it is a little more difficult. We can make a piston which is a good fit when cold, and when running under these conditions in an engine, i.e. when starting from cold - it will be quite silent but will develop a knock as the temperature increases, being due to we think its losing its good contact surface, and thereby not maintaining a good oil film on the split side as this distorts in taking up its own expansion with the increase of temperature. Also the decreased viscosity of the oil will tend to aggravate the trouble. It seems from our tests that a flexible skirt is a means of obtaining, and maintaining, the good contact surface we require under different conditions of temperature. We have tried two types of piston - which contd :- | ||