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).
The optimal number of piston rings to prevent blow past and a proposal for a new piston design test.
| Identifier | ExFiles\Box 15\3\ Scan025 | |
| Date | 10th October 1928 guessed | |
| contd :- -3- With regard to the number of piston rings we consider we should benefit by employing more than three. The Test Dept. have experienced a marked improvement on the 20 HP. chassis since adopting the five-ring piston. Considerable trouble was encountered previously due to blow past, high crank-case pressure and piston noises caused by the blow past. The slow running is also impaired by piston leakage. We think that making the number of rings less than our present standard would be a retrograde step. We admit it is possible fewer rings on the piston give us slightly less friction loss, but judging from our abserva observation during tests on the 'SS{S. Smith}' engine and the experience of the Test Dept., we think any slight gain in this direction would be considerably outweighed by other troubles. We should therefore like to test out the single bolt pedestal piston with four pressure rings and a perfect circle scraper ring above the skirt. Removing the ring from the bottom of the skirt should increase the flexibility of this part which we consider a desirable feature. The pistons fitted to 14-EX car at WW. are single bolt pedestal with 5 rings! Hs{Lord Ernest Hives - Chair}/A.C.Lovesey. | ||