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 development and testing of A.C.7. aluminium tin alloy for engine bearings.
| Identifier | ExFiles\Box 115\1\ scan0190 | |
| Date | 15th December 1936 | |
| -2- (1) Based upon the low average life of W/M.{Mr Moon / Mr Moore} bearings, Hall's Aluminium tin alloy known as A.C.7. was first tried in the form of lining and run on to steel shells similar to W/M.{Mr Moon / Mr Moore} The failure in this form was due to poor adhesion and though various experiments were tried, the poor adhesion was still in evidence, resulting in chunks of metal coming adrift from the shells. Following, the metal was then cast as a complete solid bearing both for big ends and mains, this being standardised on its test bed performance for the 4.5 Litre Bentley. Compared with previous endurance tests carried out under full throttle conditions at 4000 R.P.M., W/M.{Mr Moon / Mr Moore} bearings had an approximate life of 20 hours. The conditions were made more searching for the A.C.7. solid bearings each hour comprising the following - 30 mins. at 4000 R.P.M. 25 mins. at 4250 " 5 mins. at 4500 " Under these full load conditions the bearings stood up exceptionally well and several endurance runs were carried out without trouble up to 100 hours, and during a total of 700 hours endurance running, not a single failure was experienced. Mainly from these results the A.C.7. bearings were standardised and the first intimation of any forthcoming trouble was a big-end failure in France after 6000 miles. Prior to this, complaints were received on excessive engine roughness due to hammering of the main bearings, this being confined mainly to the rear main bearing, gradually improving towards the front of the engine. In view of the test bed results the big end failure was very surprising and the possible cause was we assumed, due to the A.C.7. facing coming adrift from the steel shim and getting into the bearing. With regard to the hammering of the main bearings, a more careful inspection and recorded Brinell figure were taken on each batch of material cast, but this as proved later was of little consequence in that during the next 15,000 French test on 4.5 Litre Bentley (B.26. G.M.IV.) a big end failed after 7500 miles (Photos graph No.12.) continued | ||