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).
Analysis of piston stop failure, attributing it to crankshaft vibration and the twisting action of the connecting rod.
| Identifier | Morton\M18\ img069 | |
| Date | 14th October 1932 | |
| Hs.{Lord Ernest Hives - Chair} from GWH.{George W. Hancock - Head Chateauroux} 14.10.32. 19-EX. Pistons Failure. The failure of the piston stops is in our opinion due to crank-shaft vibration causing a twisting action of the connecting rod of a high period. This period is transmitted to the pistons. We believe that the piston rings are held firm by the pressure on the cylinder wall. The cause then of the piston ring stops wearing away is the circular vibration of the piston, due to the whip of the crankshaft being transmitted up in a twisting action of the connecting rod, which caused the ends of the piston ring to rub on the stops. We had a very good sample of this on 19-EX. On one of the pistons taken out the piston stop had been worn down to approx. 1/32" in dia, the dust was still in the hole caused by the wear of the stop. We were able to break off the thin pip left, by lightly touching it. The ends of the piston ring were bright and polished. The piston itself showed no rubbing marks as would indicate any rolling action. There was only the bearing surface that was free from carbon. This surface was of a matt. condition rather proving that besides an up and down movement a twisting motion had taken place. We had a similar failure on the first high compression 25 HP. car, 12-G-IV, run in France. We believe that the failure would not be re-produced on English roads as the high speeds cannot be maintained. We are of the opinion that vibration is set up between speeds of 70 and 80 m.p.h. when the engine is definitely rougher than at any other speeds. It may be stated that over this speed the engine became remarkably smooth. Hs{Lord Ernest Hives - Chair}/GWH.{George W. Hancock - Head Chateauroux} | ||