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).
Correct procedure for replacing Bentley main bearings, recommending complete unit removal.
| Identifier | ExFiles\Box 115\1\ scan0254 | |
| Date | 12th January 1937 | |
| Swidn please return to Rm{William Robotham - Chief Engineer} 1020 To Rm{William Robotham - Chief Engineer} from HPS.{Horace Percy Smith - Experimental Factory Mgr} HPS.{Horace Percy Smith - Experimental Factory Mgr}6/VS.{J. Vickers}12.1.37. BENTLEY MAIN BEARINGS. Service Replacements. With reference to Sr/VA3/ET.6.1.37 in connection with the above. Whilst it would be incorrect to say that new bearings could not be fitted without first removing the crankshaft, the fitting of bearings with the unit in the frame is definitely not a practice we would care to recommend for customers' cars. The difficulty of topping a new bearing so as to obtain the correct fit and nip in its housing can no doubt be overcome in the manner described, but it would be entirely wrong to proceed afterwards to transfer a fitted bearing to another crankcase for reaming and expect to obtain on reassembly a perfectly round bearing with exactly the right amount of clearance. The suggested procedure is apparently based on the assumption that the sizing of housings is perfectly consistent, which is most improbable; if this were the case bearings could obviously be finished to size on the joint facings and subsequent fitting work would be unnecessary. There is also the question of clearances to be considered because it is obvious that unless both the new and the old bearings are of exactly the same size, either one or the other are going to do more than their fair share of the work. The reaming size of a new bearing depends, therefore, not upon the journal diameter of the crankshaft, but upon the size of the remaining bearings, which can only be determined by measurement after assembly with the crankshaft removed. For the reasons stated it is therefore considered that it would be a far more satisfactory proposition from all points of view to remove the unit and strip completely in order that the fitting, reaming and assembly of any new bearings which may be required can be undertaken under conditions which would ensure these operations are carried out with all due care and attention. HPS.{Horace Percy Smith - Experimental Factory Mgr} [Signature] | ||