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 failures after 6,300 miles and proposed modifications to prevent seizing.
| Identifier | ExFiles\Box 86\2\ scan0036 | |
| Date | 22th August 1933 | |
| X236. E.{Mr Elliott - Chief Engineer} From Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} c. to By.{R.W. Bailey - Chief Engineer} c. to Mx.{John H Maddocks - Chief Proving Officer} Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}6/MA.22.8.33. We hand you herewith two of the pistons which have been returned by GWH.{George W. Hancock - Head Chateauroux} having failed at the completion of 6,300 miles running. We think there is a reasonable chance of improvement in these pistons by altering the dimensions of the ring lands above the skirt. All these failures started on the top of the skirt and presumably the amount of deflection at this point can be limited. We find that in improving the bedding of the skirt the clearance between the bottom land and the cylinder has been increased by no less than .007" from the original 25HP. piston. There is no sign on the unbroken piston that the lands have been in contact with the cylinder wall. We have, therefore, sent a new set of pistons out to GWH.{George W. Hancock - Head Chateauroux} having the top dimensions of the original 25HP. piston and the bottom dimensions to EB500. In the meantime we are carrying out experiments to see if we can increase the diameter of this bottom land still further without running into seizing troubles. We do not want to loose this piston evidence and should be glad therefore if E.{Mr Elliott - Chief Engineer} would either preserve the parts himself or return them to us. GWH.{George W. Hancock - Head Chateauroux} reports that the top rings were gummed up on this car this is the first time we have experienced this trouble on the Bentley, and it may be due to very high oil temperatures which have been experienced in France or to the increase in clearance round the top land. Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} | ||