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).
Proposed depot sheet detailing main bearing replacement and crankshaft lubrication modifications for the 4 1/4 Litre Bentley.
| Identifier | ExFiles\Box 115\3\ scan0009 | |
| Date | 6th July 1937 | |
| PROPOSED DEPOT SHEET 4 1/4 LITRE BENTLEY. MAIN BEARINGS. (1) In reference to paragraph (1) of your Depot Sheet dealing with the 'taking up' of A.C.7. main bearings when due to hammering, the bearings sink below the joint face, we recommend the following. That the bearings are taken up in the way you describe by stopping the liners once only. If a car comes in for the second time with the same complaint of roughness and thumping due to hammered out bearings, we recommend that a new set of main bearings be fitted. These to be in the latest standardised alloy A.C.2. (not yet in Production) which has a higher Brinell to resist the hammering out. When fitting new main bearings the halves should always stand slightly proud to allow for nipping up, before reaming to size. The clearance for the A.C.2. main bearings is the same as the standard A.C.7., that is .003" diametrically. Our reason for the fitting of new bearings rather than 'liner stepping' for the second time is as follows. All the 'take up' is in a vertical plane such that, although the thump be taken out of the engine we are still left with excessive clearance on the horizontal plane. This allows for a big oil escape and consequently the big end bearings tend to be shy of oil. Seeing that the crankshaft has to be removed to fit new main bearings advantage should be taken of carrying out the following modifications to the oil holes in the crankshaft for improved lubrication to the big ends. (a) An extra and opposite hole drilled in each crankshaft journal as EB.163. (b) An extra and opposite hole drilled in each crankpin .125" dia. The crank to be thoroughly cleaned and every burr removed. The resultant of the above modification is that there are 2 - .2187 dia. holes in each journal and 2 in each crankpin, the original .2187 dia. and the other .125 dia. (2) There are several conditions to be noted when a big end bearing fails and should be dealt with as follows:- continued | ||