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 performance and failure modes of different big end bearing materials and designs.
| Identifier | ExFiles\Box 97\1\ scan0014 | |
| Date | 15th December 1936 | |
| -4- The effect of increasing the groove area on the intermediate main bearings is to improve the supply to Nos.2 and 5 big end bearings which are the worst off in this respect and in the majority of cases are the ones that fail. On the 3½ Litre Bentley having no grooves whatever in the intermediate main bearings, big end failures were confined more or less solely to either No.2. or No.5. (3) Big End Bearings. The material as tried in our recent tests has been Hall's A.C.4, A.C.2 and A.C.1., also RR.56. in the form of solid big end bearings. In the A.C. series the number represents the percentage of tin in the alloy and are all cast with the exception of A.C.1. which is the forged version of A.C.2. As seen from the following figures the less the tin element the stronger the alloy, with a higher Brinell. Of the failures this follows through in that a seizure with standard A.C.7. and A.C.4. results in a completely broken up bearing which before the engine is stopped the rod is flapping about and liable to come through the crankcase or damage the cylinder head. A.C.2 failures result in seized bearing without breaking up. A.C.1. results in plain seizure without breakage and in one particular case has rolled out and finished by shearing the shims and running round the connecting rod (Photo.No.5). In the single case of R.R.56. this seized the engine solid, though in all seizures the crankpins have not been badly damaged and easily cleaned up. Material Max.Stress Yield Pt. Elong. R.A. Brinell. A.C.7. 9.3 7 3.5 5.0 45 A.C.4. 10.7 9.2 2.7 3.5 55 A.C.2. 15.2 12.0 1.3 1.0 85 A.C.1. 26.0 18.5 12.0 22.0 127 RR.56. 28.5 24 10.5 18 132 The only type of bearing which stood up to the ¼ load conditions with standard lubrication was RR.56, which ran 10 hours without trouble. (Photo. No.6) continued | ||