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).
Service instructions for addressing bearing roughness and thumping on a 4¼-Litre Bentley.
| Identifier | ExFiles\Box 115\1\ scan0214 | |
| Date | 16th December 1936 | |
| 1020 Hd.{Mr Hayward/Mr Huddy} from Rm.{William Robotham - Chief Engineer} (for Depot Sheet). Rm{William Robotham - Chief Engineer}6/R.16.12.36. BEARINGS - 4¼-LITRE BENTLEY. (1) When a car comes in for roughness and thumping with the above type of bearings it is usually confined mainly to the rear main bearing which has hammered, graduating less to the front bearings. The procedure should be as follows:- Remove the main bearing caps only, and measure by clock the amount of sinkage below the surface of the crankcase shim face. Replace the steel shims which have Hall's metal facings by solid RR.56 shims. Leaving the part of the shim which actually faces on the bearing section at standard thickness of .100", reduce the remaining portion which joints between the cap and the crankcase by the amount of sinkage as measured. This is clearly shown on the attached sketch Rm.{William Robotham - Chief Engineer}271. With regard to the cap half, the sinkage can be recovered by machining off the joint faces of the cap. Following these modifications the crank and bearings to be oil pressure tested. Wear without sinkage can of course be taken up in the normal way by reducing the shim in its overall thickness by the requisite amount. If for any reason a new set of main bearings have to be fitted or the existing ones completely removed, then the modified grooves Rm.{William Robotham - Chief Engineer}244 should be incorporated in the intermediate main bearings. (2) Whilst the lower half is removed and the main bearings are being overhauled, the connecting rod bearing caps should be removed to inspect the shims and the bearing surface. If there is any sign of the Hall's facing breaking away from the shims, then these should be replaced by shims in solid RR.56. Unless it is necessary to take up for wear then the RR.56 replacement shims should be made exactly the same thickness as the ones removed. Providing the bearing surface is good without signs of failure, then there is no necessity to remove the connecting rods which entails removal of the head and decarbonising, etc. | ||