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).
Road failures and issues related to B.2.LS and AC.2 bearings in cars.
| Identifier | ExFiles\Box 114\3\ scan0046 | |
| Date | 5th December 1938 guessed | |
| - 2 - (2). Of these ten, four resulted in failures on the road, and in the case of B.2.LS. the big end came through the crankcase and the repair bill was £110. This particular car was a Bentley Trials, as was also the second one which failed at Oxford. In neither case had there been apparently any warning, as although they were Trials cars they were passed over for the runs on which they failed as being in first class condition, and I therefore believe that the failure was rapid, occurring completely during the two runs in which failure occurred. These two cases are a graphic illustration of the instability of the material, as both chassis were examined at Derby round about a mileage of 10,000 and passed as in first class condition. (3). The oil flow test in the case of AC.2 material when it indicates close fitting bearings is not to be relied upon, as the ageing of the material reduces the clearance, and therefore appears to show that the bearings are rather above standard, when as a matter of fact the bearing clearance has been reduced by the ageing and the engine is therefore in a precarious condition. (4). It now appears to me certain that cars fitted with AC.2 bearings in the hands of high speed drivers would be less prone to fail owing to the fact that the increased wear engendered by the high speed running completely counteracts the growth of the bearing during the ageing, and as the ageing is a slow progess the wear of the bearing increases somewhat faster than the ageing growth, which would cause trouble. Conclusion. In view of all the facts, and particularly from the appearance of the five sets of bearings taken from the cars quoted above, I am satisfied that it is dangerous to leave cars on the road with AC.2 bearings, as we are liable to have sudden failures if and when an owner after running fairly steadily for a period gives a car an all-out run, as the lighter work would result in bearing growth, reducing the running clearance to what is a danger point when the car is run at high speeds under such decreased clearances. BY.{R.W. Bailey - Chief Engineer} | ||