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).
Technical discussion on crankshafts, counterweights, and the properties of materials like cast iron and steel for crankcases.
| Identifier | ExFiles\Box 25\3\ Scan361 | |
| Date | 13th November 1928 guessed | |
| contd :- -5- make a single crank in two short bearings turn safely up to 7000 r.p.m. On some cars only a few counter weights are used, on those journals where the loads are likely to be high due to the arrangement of the cranks. Sometimes on shafts with large spans between main bearings, counter weights are placed in the centre of each span, to reduce centrifugal distortion, instead of providing another main bearing. Disc webs and extended webs are also steps towards better local balance. CRANKCASES. There is no doubt that rigidity and reduction of vibration is the principle reason for using cast iron for the crankcases on a lot of cars, particularly in America. We should expect to find the freedom from vibration inversely proportional to the modulus of elasticity of the crankcase material, other things being equal, and some values of this are :- Aluminium 10,000,000 lbs/sq.in. Grey cast iron 12/ 20,000,000 " " " White " " 20/ 25,000,000 " " " Mild steel 30,000,000 " " " This means that the stretch produced in a bar of aluminium by an applied load would be three times that if the bar were steel, and nearly twice that if it were cast iron. When doing crankshaft torsional vibration tests we have observed that 1-G-1 engine is far smoother than a std. 20 HP. having the same crankshaft, conn. rods, and spring drive. The lower periods can hardly be picked out at all, and the contd :- | ||