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 causes of and solutions for piston scuffing on experimental Wraith engines.
| Identifier | ExFiles\Box 145\3\ scan0170 | |
| Date | 5th April 1938 | |
| To By.{R.W. Bailey - Chief Engineer} from RM{William Robotham - Chief Engineer}/Mths.{Reg Matthews} c. Ms. c. RHC.{R. H. Coverley - Production Engineer} c. Ds. c. Ex. c. Da{Bernard Day - Chassis Design}/Jnr.{Charles L. Jenner} c. Rm{William Robotham - Chief Engineer}/GWR. Rm{William Robotham - Chief Engineer}/Mths.{Reg Matthews}1/WH.5.4.38. PISTON SCUFFING. We have recently been experiencing considerable trouble with "scuffed" or partly seized pistons on experimental Wraith engines. The trouble first became apparent with the use of low viscosity oils and higher pressure rings, but we have now established that neither of these items were a direct cause of "scuffing". Our tests to date have established the following facts :- (1) A plain mineral oil such as Castrol 'XL' or Mobiloil 'Arctic' is not an ideal lubricant for running in purposes when used in the new condition. (2) Moderately higher pressure rings are not a cause of "scuffed" pistons. (3) Oil viscosity has no bearing on piston "scuffing". (4) Castor oil is one means of avoiding piston "scuffing". (5) No scuffing occurs when a plain mineral oil which has been used before and cleaned thoroughly, such as oil used on Production De Laval test, is used. (6) Tin plating enables any oil to be used for running in purposes. (7) It does not necessarily follow that a bore which has previously "scuffed" a piston and has been cleaned up, will "scuff" any new pistons fitted to that bore. (8) We should say that in about 90% of the cases of "scuffing" the pistons "iron" themselves out and no serious damage occurs. (9) After completing the "running in" period on De Laval oil it is quite safe to run on straight mineral oil thereafter, without "scuffing" occurring. RECOMMENDATIONS. (1) Continue to "run in" on Mobiloil "A" De Laval oil as used at the present time for production engines. Cont'd.{John DeLooze - Company Secretary} | ||