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).
Investigation into crankshaft and main bearing failures, wear, and subsequent modifications.
| Identifier | ExFiles\Box 83\1\ scan0241 | |
| Date | 10th October 1936 guessed | |
| ( 2 ) CRANKCASE & BEARINGS. LOP EB.2737. Existing, complete to above LOP incorporating:- EB.2898 Crankcase T?H.{Arthur M. Hanbury - Head Complaints} EB.1855 Crankcase L.H. Main Bearings in Hall's Solid Metal (latest cast) RM.{William Robotham - Chief Engineer}67 Rear Main Bearings. Groove continued round the inter.bearing. At 9,000 miles we became aware of the crankshaft thumping in the main bearings which produced a rough period extending from 1500 to 2500 rpm. The movement could be felt by lifting the crankshaft by means of a lever through the clutch inspection cover. Examination showed that the bearing shells were loose in the caps, and an oil test showed that Nos. 5, 6, and 7, were progressively worse than the front bearings. Experiments were made to reduce the roughness by means of small balance weights on the rim of the flywheel. Steel strips equal in weight to four 3/8" full nuts, fitted level with the BDC mark effected a big improvement. Investigation of the balance of the crankshaft flywheel and clutch as a unit, would help to explain this and show if the slack in the bearings was caused by incorrect balancing. If this is not the case, the failure indicates that the bearing loads are too high for these bearings and that in order to prolong their life, the maximum engine revs should be reduced until more reliable bearings are available. The trouble was followed by oil leaks into the clutch housing and from the engine front past the fan pulley. The unit was dismantled for examination by G.W.H. at 16,222 miles. The main bearings had fidgeted in the case and caps, which showed uneven wear; the bearings had lost their original curvature with the hammering so that they were tight on their sides and loose up and down. Owing to these deformations and the clearances which were present, the shims no longer held the bearings firmly in the case, so that it was impossible with ordinary tackle to force them into complete contact with the case and caps, and measure the internal diameters at the same time. The bearing surfaces were in good condition and had worn very little. The crank journals showed excessive wear in excess of .003" on N° 7. The total play in the rear main bearing was found to be .011" as far as the limitations referred to allowed it to be measured. The fan pulley boss had touched the front engine case as a result of the play in the bearings, but had not been audible during the running. Handwritten Notes: [Left margin, top] L Smith Report required. [Left margin, bottom] Swell. accurate figures required from the shop This figure also before engine stripped to check up on Chateauroux measurement. | ||