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).
Results of tests on various modified pistons for Wraith and Bentley models.
| Identifier | ExFiles\Box 148\3\ scan0405 | |
| Date | 4th October 1938 | |
| To Rm.{William Robotham - Chief Engineer} from Rm{William Robotham - Chief Engineer}/OTS. Rm{William Robotham - Chief Engineer}5/R.4.10.38. P I S T O N S. In accordance with Byl/G.15.7.38., a straight-forward test has been carried out to determine whether there are any detrimental effects from the alterations suggested in the memo. The attached photograph shows. Piston No.1. A standard Wraith piston, the only modification being, the top land increased by .004 (dia). Piston No.2. (EW.1882-3). A standard Wraith piston modified as follows:- The top land increased by .002 (dia.) and width of top land reduced from .250 to .125. Piston No.3. EB.3122. A standard Bentley piston (Aerolite). The result shows that an increase of .004 is too much, causing a hard rubbing of the aluminium, while an increase of .002 keeps the top land sufficiently clear of carbon without rubbing too hard. The suggested piston for production is shown on ECD.911. This has not been tested, but it only differs from the tested piston No.2 by the top land width being .200 instead of .125. The latter is the more severe test, so these pistons are still being run, and if they continue to do so satisfactorily, we consider that ECD.911 will be satisfactory for production. Cars will be fitted up with the latter as they become available. Running Time. No.1 piston completed 12 hours full throttle @ 4,000 R.P.M. No.2 piston completed 7 hrs.10 mins. full throttle @ 4,000 R.P.M., when the test was broken down by a valve failure. Rm{William Robotham - Chief Engineer}/CTS.{C. Trot Salt - Carburation} | ||