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).
Failure of narrow pin crankshaft bearings and proposals for improvements, including material tests.
| Identifier | ExFiles\Box 82\3\ scan0342 | |
| Date | 1st June 1935 | |
| X 201 a To E.{Mr Elliott - Chief Engineer} c. to Wor.{Arthur Wormald - General Works Manager} c. to By.{R.W. Bailey - Chief Engineer} HS{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}1/KW.1.6.35. Narrow Pin Crankshaft Bearings. You will have observed that a big end has failed on the test in France. The car there is of course fitted with a narrow pin crankshaft and strip lead bronze bearings. The failure in this case was undoubtedly due to the method of securing the big end bearing from turning being insufficiently strong mechanically. We are proposing to let the car complete 15,000 miles on the remainder of these big end bearings, and then we are going to replace them by some having a greater wall thickness. The wall thickness dictates the strength of the tab which prevents the bearings turning. To establish the narrow pin crankshaft is in our opinion of vital importance on the Bentley, because we have got to live with the 6-cylinder engine for a considerable time and when we come to the large bore unit the car will be tending to run at higher engine speeds and therefore nearer to the critical crankshaft period. The attached analysis shows that with the existing engine the narrow pin connecting rod bearings are no more heavily loaded than those of the Kestrel, and by increasing the length by 1/8" we can keep the loading the same with the large bore unit. It is interesting to know that the main bearings on the engine in France are breaking up, which indicates that we have got to get a main bearing which can stand higher oil temperatures than the existing white metal. For this reason we are pushing on with the tests on Hl's metal and the high cadmium bearings. We have always been of the opinion that we ought to be able to make the narrow pin crank engine smoother than the present standard as the crankshaft is undoubtedly stiffer, and now that Hancock has got the correct slipper wheel loading he seems very pleased with the absence of vibration. | ||