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).
Letter to Bentley Motors regarding the methods and challenges of maintaining bearing clearances on Bentley engines.
| Identifier | ExFiles\Box 146\3\ scan0274 | |
| Date | 24th December 1936 | |
| To Bentley Motors Ltd Derby................... Rm.{William Robotham - Chief Engineer} copy to ................ Hd.{Mr Hayward/Mr Huddy} 1245 Levallois Sr/VA3/GM.24.12.36 re: Stepping of bearing liners on Bentley engines. Maintenance of bearing clearances. With further reference to your Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell}4/JH.18.12.36 ( paragraph 8,9 & 10 on page 2), we do not know of a practical method of determining the exact amount of the final bearing clearance left after the stepping of the upper face of the liners and reducing the joint faces of the caps, in order to take out slack on the outer diameter of the bearings, with the crankshaft in position. As you are aware, there are certain difficulties encountered when trying to ascertain the resultant clearance between the crank journal and the bearing after the stepping of the liners and the reducing of the joint faces of the cap (crankshaft in position) which are as follows:- 1. Oil film between the upper bearing and the crankcase. This may be negligeable. 2. Wear and ovality of the crank journal (Assuming that a car has covered from 15.000 to 20.000 kilometres) 3. Bearing wear (this may not amount to very much). 4. Varying amount of sinkage of each of the 7 main bearings into the crankcase upper half. Concerning the wear of crankshaft main journals, we as reported to you recently, took measurements of the crankshaft journals of B.74.GA Mr. Patrick LE BLAN, the car having, at the time, covered 20.385 Kms.. We found the max. diameter of No. 5 journal to be 2.2465" and the min. diameter has 2.2455". We have thought of the idea of placing a piece of lead wire of suitable thickness between the bearing and the crankshaft, then tightening up the cap and then measuring the wire after it has been flattened out. We have in the past tried out this rather old method on 20 HP. Phantom I and II engines, but we found apart from it not being accurate enough that there was a risk of deforming the bearing and a possible risk of also deforming the caps of the intermediate bearings. We ourselves think the following method may be the best. ..... | ||