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).
Investigation into piston scuffing in Wraith engines and proposed experimental solutions.
| Identifier | ExFiles\Box 9\1\ 01-page14 | |
| Date | 2nd February 1938 | |
| 2.2.38. the material, which in all cases is R.R.53. Taking the first three Wraith chassis in the table, which were all new engines, we find they have seized when using either Motorine "C" or Mobiloil "Arctic" oil and with either high or low pressure scraper rings. The 4th. chassis was not new but had a honedoutbore which had previously been lightly scuffed" in this case we had a new set of pistons and standard rings throughout and as we could notafford to scuff this set of pistons which were the only ones available in works, we decided to run in on Castor oil, since this oil had helped us considerably in the past. After running in and subsequently after a 2 hours oil consumption test run on Motorine "C" the pistons were found to be quite free from tight marks. Production have not been experiencing any trouble with piston scuffing on the 25/30 piston which is identical with the Wraith piston except that on certain Wraith engines we have used higher pressure rings. The cylinders in both cases are produced without chills in the bores and are similar in design. The distortion of the Wraith cylinders with the head bolted on, we found to be similar to 25/30 H.P. so that nothing unusual in bore dimensions was causing the trouble. The first production Wraith engine was fitted with high pressure compression rings and run in with De Laval oil which is not new oil and is Mobiloil "A" which is a mineral oil. It appears that new mineral oil is not a good thing for running in engines and particularly so when R.R.53 alloy pistons are used in conjunction with cylinders produced without chills in the bores. In order to overcome the trouble we intend to make the following experiments - (1) Standard pistons and rings in bore without chills using Motorine "C" oil. (2) Standard pistons and rings in bore produced with chills in the bores. (3) Effect of tin plating the pistons. (4) Effect of old oil as used on De Laval. (5) we should like to try the effect of graphite during the running in process only, since graphite is particularly good for Cast Iron. Rm{William Robotham - Chief Engineer}'/Mths.{Reg Matthews} | ||