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).
Analysis of possible causes for a series of engine failures, focusing on crankshafts, bearings and oil system blockages.
| Identifier | ExFiles\Box 124\2\ scan0352 | |
| Date | 11th September 1941 | |
| -2- Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden}1/JH.11.9.41. Until it was suggested by Jnr.{Charles L. Jenner} that the oil hole could be obstructed despite the oil flow test a number of other possibilities had been considered. In the remote event of the obstruction proving to have resulted from disintegrated bearings these possibilities may have to be taken up again. Briefly they are as follows - 1. There are signs on all the connecting rod bearings, the pistons and the crankshaft journals that the pistons and rods have been inclined slightly towards the rear of the engine. Coupled with this the crankshaft appears to have been riding forwards excessively. This could result in failure of the only thrust shim called upon to take the load, i.e. the shim at the centre bearing, and the subsequent failure of the bearing. If the cylinder centrelines were not perpendicular to the crankshaft centreline, but sloped slightly to the rear, this effect would be caused. Also the effect would be proportional to main bearing loading, which, higher up the range, means piston inertia and square of the speed. 2. The cylinders and their jacketing help the crankcase proper to resist longitudinal bending. The main bearings, however, are in the rigid crankcase proper, and weakness in the cylinder portion can hardly be expected to cause displacement or misalignment of the bearings. It is not therefore thought that the water jacket crack has any bearing on the failures. Jnr.{Charles L. Jenner}, however, is still not happy about the centre bearing pedestal and thinks there is a possibility of a crack which opens under conditions of high load and temperature. 3. It has been suggested by Jnr.{Charles L. Jenner} that the first three failures were due to a faulty crankshaft, and that the oil holes subsequently became blocked and caused the fourth failure. In support of this, and forgetting By's. findings, the crack in the crankshaft would be expected to open up at high speeds when going through the 4th. major critical vibration. If the obstruction proves to have come from the foundry this supposition only holds good, if the sand had floated around the oil system until quite recently without building up. Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden}1/JH | ||