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).
Depot sheet concerning main bearing failures and replacement procedures for the 4¼ Litre Bentley.
| Identifier | ExFiles\Box 149\2\ scan0171 | |
| Date | 19th October 1937 | |
| DEPOT SHEET. Juler 1020 19.10.37. 4¼ LITRE BENTLEY - RE: MAIN BEARINGS. We have arranged in view of the sudden failures of engines which have not shewn roughness or knocking, to institute an oil flow test which will indicate when the main bearings of an engine are in dangerous condition due to wear. GWH.{George W. Hancock - Head Chateauroux} at Kingsbury is making the necessary tests to give the date on which Depots will replace the bearings with the new AC.2. material. In addition, in future no 4¼ with A.C.7 main bearings will be "taken up", they will when worn or hammered to such a state as to fail on the test referred to above, be replaced by AC.2 bearings with .002 nip on each half of the bearing, giving a total nip of .004. At the same time connecting rod big ends will be examined, and if they are slack in the rods they will be replaced by new bearings with a positive nip of .002 on each half of the bearing, giving a total "nip" of .004. This amount of "nip" is demanded in order to cover the minus limit on the bushes as originally produced, and the plus limit in the rod; when, however, the later bearings become available which have been specified with an interference fit of three quarters of a thousandths, then it will be desirable to reduce the "nip" to .001 on each half of the bearing or a total "nip" apart from the interference fit of the shell in the housing or rod of .002. | ||