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).
Experiences with Bentley and 20/25 pistons, focusing on issues with castings and the benefits of ageing.
| Identifier | ExFiles\Box 86\2\ scan0165 | |
| Date | 28th November 1933 | |
| To Hs.{Lord Ernest Hives - Chair} from E.{Mr Elliott - Chief Engineer} c. Sg.{Arthur F. Sidgreaves - MD} Wor.{Arthur Wormald - General Works Manager} By.{R.W. Bailey - Chief Engineer} Mx.{John H Maddocks - Chief Proving Officer} x236 E.4/HP.28.11.33. Pistons. I have been talking to Mx.{John H Maddocks - Chief Proving Officer} about his experiences with Bentley and 20/25 pistons. He has recently taken down two trials car engines, one of which had done six thousand and one seven thousand miles, and the condition of the pistons he has described as practically perfect. Also the chalk test has not disclosed any cracks. These pistons were put through the same routine as the 20/25 in respect to light running and running in, this process being in no way shortened or accelerated even in spite of the great urgency attached to these trials Bentleys at the time. Both of these cars have had a gruelling time and one of them has done part of its demonstration work in France. The standard 20/25 piston from which the bentley was developed is also giving very good results, and piston troubles have become a thing of the past. It is true that some time ago a holdup was experienced with seized and distorted pistons on the 20/25 production, but this was traced to piston castings being fed on to the machines as soon as they arrived in the stores from the foundry. When the castings were taken from the back of the shelf corresponding to about a fortnight or three weeks ageing, all troubles and difficulties disappeared. Mx.{John H Maddocks - Chief Proving Officer} from his experiences is convinced that the aluminium piston cannot be hurried as the material requires time for the physical changes which occur before it reaches the final state of a completely run in piston. We are in full agreement with him on this point and we believe the importance of a sufficiently long period of light running followed by incremental loading cannot be overstressed. | ||