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).
Advantages and proposed procedures for using Aluminium Alloy bearings over steel-backed bearings with white metal liners.
| Identifier | ExFiles\Box 115\3\ scan0097 | |
| Date | 16th November 1937 | |
| -2- RHC{R. H. Coverley - Production Engineer}/SB.{Mr Bull/Mr Bannister}6/MJ.16.11.37.Con When steel backed bearings were used it was possible to attain much greater accuracy because the final liners could be correctly surface ground, furthermore, the white metal liner facing being soft and of the same nature as the bearings facilitated reaming and ensured a satisfactory bore, regarding size. The present Aluminium Alloy materials are much harder than white metal which renders accurate sizing difficult due to the rapid reamer wear, and in addition the liners are of a much harder Brinell than the bearing itself which creates an unsatisfactory condition due to the unbalanced cut and unless great care is taken the bearings are liable to be oval. The rotation or creeping of bearings without liners would be prevented by the 'nip' allowance in the housing assisted by one dowel which is quite sufficient because the coefficient of expansion of the bearings is approximately similar to the crankcase. This ensures that the original 'nip' is maintained when the crankcase is in a hot condition which of course would not apply with steel backed bearings. The only objection to this scheme appears to be with repairs, but it would be possible to supply Depots with bearings in a finished condition which would render it necessary to merely remove the old bearings, replace with new and reassemble. This would again ensure that relative alignment of crankshaft and camshaft are not disturbed when fitting new bearings, thus helping to eliminate troubles encountered with noisy timing gears after engine overhauls. It is therefore considered that Repair Depts. would profit in this direction to an extent which would more than compensate for the deletion of liners and the advantages claimed for this feature. The old bearing shells removed during overhaul could be returned to the Works and re-melted subject of course to the correct material analysis being maintained. Wraith engines without main bearing liners have already satisfactorily complete 3,000 miles running, and it is proposed that the temporary steel liners used for boring shall be retained for use with the true half bearing (until the existing stock of crankcases is absorbed), after which additional metal may be left on the bearing caps and crankcase to compensate for the deletion of liners. This procedure can also be applied to connecting rods in addition to crankcases, and would result in a much higher standard of accuracy in assembly because machine accuracy would be maintained and fitting skill entirely eliminated. RHC{R. H. Coverley - Production Engineer}/S. Bannister. | ||