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).
Conclusion of a report on main bearing failures, comparing the effects of balanced versus unbalanced crankshafts.
| Identifier | ExFiles\Box 115\2\ scan0378 | |
| Date | 10th January 1939 guessed | |
| - 4 - (3) Conclusion. In general the failures of main bearings occur at the end journals or on the thrust faces of the centre journal; the centre and intermediate journals carry the highest loads and so the load on the bearing is not necessarily a criterion of whether the lead bronze will break up, the extent of shock loading above a certain stress seems to be the most likely cause of breaking up, removal of the balance weights reduces the magnitude of this shock load and at the same time reduces the obliquity of the shaft at the moment of highest shock loading. In view of the cracks in No.4. main bearing panel on Kestrel, the crankcase for Peregrine was stiffened and the main bearing studs put deeper into the bosses to even out the load distribution, so that there should not be any further trouble in this direction, even with an unbalanced shaft. The unbalanced shaft weighs 19 lbs. less than the balanced type, and so, if the balance weights can be removed without detriment to the engine in other ways, it would be a definite advantage. The objections to an unbalanced shaft are mostly due to the higher centre main bearing loads and consequent loads on the centre bearing panel. The latter has been redesigned to meet this trouble. From the foregoing analysis it will be seen that for the same speeds with higher M.E.P's. the end main bearing is less affected by shock loads with an unbalanced shaft than with a balanced one. The experience with Peregrine I No.3. bears this out and as future development will probably lie in the direction of increased M.E.P. it would probably be better to use an unbalanced shaft in further work on these engines. Lr{Mr Ellor}/Lov{Mr Lovesey}/Ply. Att. Photos. KF.6,10,12,15 and 17. Blueprints 1,2 and 3. Appendix. | ||