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).
Pros and cons of different crankshaft bearing arrangements and related material choices.
| Identifier | ExFiles\Box 103\3\ scan0177 | |
| Date | 2nd August 1933 | |
| To WCR. from E.{Mr Elliott - Chief Engineer} c. Hs.{Lord Ernest Hives - Chair} By.{R.W. Bailey - Chief Engineer} Bn.{W.O. Bentley / Mr Barrington} J.3. Crankshaft. Memo Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}4/KT.31.7.33 raises an issue which we have had under review for some time, e.g. the question of departing from what has always been Rolls-Royce practice of having a mainbearing on each side of each crank throw. We think there is little doubt that the best alternative arrangement from a bearing loading point of view, is the four bearing crankshaft which is so generally in use, although on the occasions when "R" considered this problem he had leanings towards the three bearing design arranging the engine in two groups of three. This latter scheme has good induction port spacing for a single carburetter, Nos. 3 and 4 being the maximum distance apart, but the centre bearing loads are very high and the crankshaft span calls for exceptionally large crankpin diameter. We, therefore, consider the four bearing arrangement the only reasonable one and have to accept the disadvantage of ports 3 and 4 being close together failing some means of wriggling them apart in the design. Actually the crankpins of the four bearing shaft have to be made larger in diameter than on the seven bearing scheme, on account of increased span and this runs us into a difficulty in assembly due to the interference fit of the gudgeon pin in the piston. The con rod big end on J.3. only just passes through the cylinder bore now. We have been pursuing enquiries for some time through HL to find a suitable steel for gudgeon pins with a larger coefficient of expansion which in combination with a lower expansion piston metal would enable us to assemble and pull apart pistons and rods without heating. There is a Nickel Chromium Manganese steel in view at the moment for this purpose. | ||