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 Leyland Motors discussing the causes of crankshaft failures in diesel engines.
| Identifier | ExFiles\Box 140\3\ scan0131 | |
| Date | 1st January 1938 | |
| 1175 also p. Rml/R.{Sir Henry Royce} 1st January, 1938. W. West, Esq., Leyland Motors Ltd., LEYLAND, Lancs. Dear West, I was very interested in your paper. The only point I would like to comment on is the exceedingly rapid failure of your cast cranks in the diesel engines. In the first place, our experience hardly agrees with the statement that the stressing of crankshafts is largely the result of mal-alignment or wear of the bearings. We do not recollect having a crankshaft failure that could be attributed to this cause. Our failures are usually either (1) Aero. ) Fatigue failure due to over-stressing 12-cyl. ) the shaft due to the high M.E.P's necessary and the necessarily light weight of the crankshafts. (2) Car. ) Almost invariably due to the crankshaft 6-cyl. ) vibrating torsionally at its natural frequency, due to exitation caused by the regular explosion or inertia loads imposed upon it producing resonance. Most six throw crankshafts to-day, in engines between 3&7 litres displacement, when fitted with a flywheel and connecting rods have a torsional vibration frequency of between 12,000 and 24,000 cycles per min. In a 6-cyl. engine there are three explosions per revolution, and, therefore, with a shaft having a 12,000 per min. frequency, at 4,000 R.P.M., the explosion impulses are exactly in step with the cranks torsional oscillations & resonance occurs | ||