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 ring experiments, detailing issues with L-section rings, blow-by, oil consumption, and proposed solutions.
| Identifier | ExFiles\Box 144\3\ scan0108 | |
| Date | 11th August 1936 guessed | |
| -/4- We cannot definitely explain why the L section ring is so effective and maybe due to any or a collective result of the following. (a) Improved scraping as the shape of the ring suggests. (b) Gas inside the ring forcing it on to the wall. (c) Gas pressure trap in the L section forcing the ring as a seal on the bottom of the piston ring groove. (d) Oil filling the L section, sealing any further leak, by virtue of the gas pressure on the top side of the ring. MX.{John H Maddocks - Chief Proving Officer} reported a considerable improvement by fitting stops in the existing piston ring groove which we confirmed by a run on the test bed. Running at 4000 R.P.M. with the air intake breather removed, the consumption figure improved from 300 miles/gallon under standard conditions to 800 miles/gallon. The blow by the stops caused an excessive crankcase back pressure, so much that oil was leaking everywhere possible. If on the other hand the breather to intake was connected up, the oil consumption was down to 200 miles/gallon due to the amount of oil vapour being blown into the intake by the excessive back pressure. In a normal engine where there is little or no blow by, disconnecting the breather makes no difference to the consumption figure. Again in the case of the stopped ring piston, the improved result is not due entirely to the fact that the rings being stopped they bed to conform with the bore, as the result is immediate. How much we cannot yet say, but the gas leak, past the unsealed stops is, we are convinced responsible in some way to the improvement. Though a four ring piston with stops has been drawn to Lec.5206, and is being produced for experiment, the disadvantage is that the rings are more liable to stick, the breakage of stops and leaks past the unsealed stops. | ||