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).
Engine roughness and vibration on chassis B. 154 GA, detailing modifications to main bearing liners.
| Identifier | ExFiles\Box 146\3\ scan0188 | |
| Date | 29th February 1936 | |
| Bentley Motors (1931) Ltd., DERBY.....................Rm.{William Robotham - Chief Engineer} copy to Hd{Mr Hayward/Mr Huddy} (Works). H.{Arthur M. Hanbury - Head Complaints} Iles Sr/VA.I/Crn.30.II.36. SWPC chassis B. 154 GA - M.{Mr Moon / Mr Moore} Perroud. Total mileage ... 8,000 kms. During a road test which we carried out on this car, we observed that there was a very bad engine period, or engine roughness, at about 900 r.p.m. when the engine was pulling, and there was also a very bad period (engine vibration) on the over-run at 2,800 r.p.m. After referring to your memo. Rm{William Robotham - Chief Engineer}6/R.17.II.36. to which you attached a copy of Hd{Mr Hayward/Mr Huddy}'s report on the work carried out by the Repair Department to cure the thud in Raymond May's Bentley, B. 24 GA, we decided to inspect the lower halves of the main bearings. We removed the lower half, and tested the bearings under oil pressure. There was an abundant oil flow from the rear and intermediate bearings. We dismantled the bearing caps and found by measurements taken with a clock that the lower half of the rear bearing had sunk .003" into the cap. We filed the joint faces of the cap, so as to bring same level with the joint faces of the lower half of the bearing. As far as we were able to ascertain with the crankshaft in position, we judged that the upper half of the rear bearing had sunk by .004" into the upper half of the crankcase, or that the joint faces of the upper half of the rear bearing were lower by .004" than the corresponding joint faces of the upper half of the crankcase. It would be obvious that reducing the liners in the ordinary way would not reduce this play. We then decided to 'step' the upper faces of the liners, by filing them in such a way that the thickest part of the liner would put a load on the joint faces of the upper half of the bearing, as per attached sketch. The upper faces of the liners of the remaining bearings were "stepped", as per figures given below :- .002" for N°1 bearing .003" " N°2 " .005" " N°3 " .005" " N°4 " .003" " N°5 " .004" " N°6 " ................ | ||