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 breakage on a 20 HP chassis and proposing design modifications to the piston rings.
| Identifier | ExFiles\Box 16\1\ Scan202 | |
| Date | 7th July 1928 | |
| BY.{R.W. Bailey - Chief Engineer} from E.{Mr Elliott - Chief Engineer} c. to BJ. Hs.{Lord Ernest Hives - Chair} Handwritten: X741 E6/M17.7.28. 20 HP. PISTON. X.741 X.5040 We have not yet seen any report, or the broken pieces, of the piston which went to bits on the low geared 20 HP. chassis, but we are working on the assumption that it is the same type of breakage as the Phantom, which was met by strengthening the diagonal web etc. We send herewith Lec.2577 which illustrates the various points mentioned in R's last telegram on this subject. The number of rings on this piston have been reduced from 5 to 4, but all are now pinned. It is thought that the 4 pinned rings are equal in value to 3 pinned and 2 not pinned. A number of different combinations of rings are shewn in the lettered diagrams, which should be tested for oil scraping properties, and as substitutes for the 'L' shaped rings at present being used on production. It is thought that the type of 'L' shaped ring in which part of the surface in contact with the cyl. is cut away is quite a good scraper ring, but cannot be used in all the rings of the piston because its gas holding properties are impaired by the groove. To overcome this disadvantage we have suggested a special ring illustrated in the diagram D.{John DeLooze - Company Secretary} in which the oil collecting cavity consists of a number of gashes round the lower edge of the ring. As the cavity is not continuous the gas holding property of this ring is not impaired, and it can be used in all the grooves of the piston simultaneously. This ring is considered to be quite a promising substitute for those at present in use. Age and wear should not spoil its efficiency if it has any oil scraping properties at all. The various other points of interest in connection with the piston are enumerated on the drawing. As regards the question of weight the saving of one ring and of some metal around the inside circumference of the head should go far to counterbalance any additions made for strengthening the piston in the locality of the break. The angle between the diagonal webs has been left unaltered with a view to utilising the present dies, if it is found possible to modify same. E.{Mr Elliott - Chief Engineer} | ||