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).
Test results of AC.9 main bearing material for Bentley 'M' Series chassis engines.
| Identifier | ExFiles\Box 115\2\ scan0408 | |
| Date | 23th January 1939 | |
| Spec lde 1020 BENTLEY CHASSIS - SECOND HALF OF 'M' SERIES. RE: PROPOSAL TO USE AC.9 AS A MAIN BEARING MATERIAL. It was agreed some time ago that we should fit six engines with AC.9 well before the time when the material would normally be brought on. Three of these engines have been run and dismantled for examination, the results were :- (a). The first engine showed the bearings generally poor two of the bearings had definitely seized. The whole set of bearings was then passed over to H1/Mr.Talbot who confirmed that two of the bearings had been so hot that they were completely annealed, the brinell figure having dropped to 45 from between 75/85. (b). In the second engine the bearings were passible, but required some touching up. (c). The 3rd engine - the bearings were quite satisfactory. In view of the fact that one out of three had a seizure when fitted with bearings produced from the same batch of material and worked under exactly similar conditions, goes to show that the material is inherently unreliable, as being put forward at the moment. It may be due to foreign matter in the engine that the two bearings picked up and seized, but this is exactly what happened with the AC.2 material, and I have therefore decided that since we are only committed to a further 100 engines that we should complete these engines with AC.7 material, facing the abnormal scrap which may be involved in producing the bearings rather than create another set of conditions similar to AC.2 by which 77 cars have had to have all the main bearings replaced at RR. charge. In regard to the connecting rod big end bearings, the material appears to be satisfactory, as we have been using this for a considerable time without the slightest disability. P.S. I waited before sending the above memo out to see the result of further engines, Two further engines show definite signs of hard rubbing prior to seizing. I appreciate it will mean a hold-up, but I consider we have no alternative. BY.{R.W. Bailey - Chief Engineer} [handwritten initials] | ||