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 failure, scraper rings, and a proposed new ring design with a sketch.
| Identifier | Morton\M3.2\ img019 | |
| Date | 17th March 1925 guessed | |
| (2) valve springs and extra high compression, and run at a speed of say 3,300 RPM. for a long time. This would prove or otherwise the theory of the failure, and shew how much difference it is necessary to make so that the pistons shall be free from such a failure. Higher speeds that are likely to occur on the car or additional weight of crown could be used to prove that we had a margin of safety, but we ought to reduce the stress at the beginning of the fracture at least 50%. E.{Mr Elliott - Chief Engineer} will let us know what is being tried, but certainly do something more than materials. In passing I would like to point out that my idea of all scraper rings has the defect of making the piston less gas-tight because the gas can run round the grooves. Perhaps the grooves should be milled in and stop short of the joint - [Sketch of a piston head with rings] E.{Mr Elliott - Chief Engineer} will understand my sketch. You will also remember that the idea of bevel-ling the ring or any scheme for unequal surface pressure, will wear wrongly. It has occurred to me that a way to get this result is to put two narrow rings in one groove - one - the lower - being stiffer or have more cut out, so that its pressure on the cyl. walls shall be greater than the upper one, and so scrape downwards. The stiff or extra loaded ring will wear faster but can feed the wear for a considerable time. R.{Sir Henry Royce} | ||