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).
The comparison of bearing materials, test bed seizures, clearances, and issues with main bearings.
| Identifier | ExFiles\Box 97\1\ scan0015 | |
| Date | 15th December 1936 | |
| -5- Rm{William Robotham - Chief Engineer}/Swd1.12/AP.15.12.36. In comparison with A.C.1. in which we have had several 1/4 load failures, RR.56. appears to be the better material as a big end, so far as our tests have gone. If the two types of bearings are put on a gauge void of oil, A.C.1. tends to pluck and bind to a worse degree than RR.56. No measurable slack or distortion has taken place in the runs carried out on RR.56. The minimum clearance we have found necessary with RR.56. big end is .002. The failures experienced under 1/4 load and under road conditions with A.C. bearings is, we think, due to the high alternating load created by the inertia of the rod and the low gas pressure combined with the cap half bearings riding hard on the shaft on the upward stroke, thus destroying the oil film. Some road failures indicate thrashing of the rod from side to side on the crankpin and the insufficient bearing strength to withstand this. Tabulated are the test bed seizures under 1/4 load - Material Running Time Failures RR.56. 10 hours. - A.C.1. 7 " 2 A.C.4. 5 " 2 A.C.2. 3 " 2 Standard A.C.7. in view of number of road failures, was not included in these tests. (4) Main Bearings. The hammering out of the main bearings particularly the rear is serious, in that the engine becomes rough and the big ends are robbed of oil, the latter with possible serious consequences. This is not confined to reducing the bearing section, but also hammering out of the actual crankcase which renders any "take up" difficult. In this case actual wear in the bearings becomes a minor feature in the issue. This is a more difficult problem than the big ends as we have definitely got to get a bearing which is strong and hard enough not to start fidgetting and yet will not cause excessive crank wear. continued | ||