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).
Particulars of pistons, including ring configuration, scraper ring design, and material selection.
| Identifier | ExFiles\Box 148\3\ scan0058 | |
| Date | 8th May 1929 | |
| Rg.{Mr Rowledge} E.{Mr Elliott - Chief Engineer} } FROM R.{Sir Henry Royce} HS.{Lord Ernest Hives - Chair} X4004 RL/M8.5.29. Copy to Sg.{Arthur F. Sidgreaves - MD} Wor.{Arthur Wormald - General Works Manager} By.{R.W. Bailey - Chief Engineer} RE. PISTONS X3996 E.{Mr Elliott - Chief Engineer} is sending you further particulars as to the grinding of the pistons which have the so called 'Invar' skirt. It is understood that our standard practice shall be, whenever we are making an alteration, three narrow gas rings and a wide scraper ring all above the piston pin, all these four rings being pinned for position, which should be better than five unpinned rings. The scraper ring is understood to be of the perfect circle type with the central groove cut as side as is necessary to get the scraping action. We are proposing this type of ring because of its mechanical perfection. We understand that it can be made more and more effective as a scraper as the pressure on the lands is increased, by increasing the set on the ring, or by cutting the central clearance groove wider. It is thought that this combination of rings gives: (1) The lightest piston. (2) 3+ gastight rings (3) 3 scraper edges. It is also good and lasting, in that there is a good surface top and bottom of the ring to propel the ring along the bore of the cylinder. As regards the length of the piston we find no advantage over the moderate length shewn on our latest drawings. As regards the material we understand it is universal in our aero engines to use forged pistons of 'Y' metal, or Hall's alloy, and that our car pistons are made from castings, preferably die castings in the usual copper aluminium alloy, or in Hall's alloy, which we understand is lighter than any other alloy possessing the same strength at the high working tempera- tures. It is understood that we are not altering the diameter of the piston pin from the 23% of the cylinder diameter. R.{Sir Henry Royce} | ||