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).
Experiments to increase the critical speed of a Bentley crankshaft.
| Identifier | ExFiles\Box 85\5\ scan0068 | |
| Date | 24th July 1934 | |
| +217 To SG.{Arthur F. Sidgreaves - MD} C. to Wor.{Arthur Wormald - General Works Manager} C. to E.{Mr Elliott - Chief Engineer} C. to Hy.{Tom Haldenby - Plant Engineer} C. to RMO. C. to Bn.{W.O. Bentley / Mr Barrington} Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}16/KW. 24.7.34. Critical Speed - Bentley Crankshaft. Since trouble was experienced on test and in experimental running with flywheels being shaken loose owing to the critical crankshaft speed being reached on the Bentley engine, we have been working to improve the position in this respect. Originally duralumin connecting rods were tried running directly on the crankshaft and these gave satisfactory results as a bearing. However, it was found upon making enquiries in America that these rods were likely to tighten on the shaft under extreme conditions of cold, and for this reason the experiment was abandoned. The next step was to take advantage of the improved bearing qualities of lead bronze and shorten the width of the connecting rod bearings, adding the amount taken from the big end to the journal in the shape of a stiff section. At the same time advantage was taken of RHC{R. H. Coverley - Production Engineer}'s ability to produce a very thin strip bearing to lighten the weight of the connecting rod big end. The net result of this modification to the crankshaft and connecting rods was an increase in the critical speed of the crankshaft from 5,000 to 5,300 r.p.m. At the same time the amount of balance on the shaft was increased from 62% to 74%. 21 hours running has now been completed on this engine, the last 10 hours of which have been at 4,250 and 4,500 continuous high speed, full power endurance, and on strip the condition of the engine appears to be excellent. The engine is now being re-built and run on the road. | ||