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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).
Technical letter discussing bearing material performance, oil supply issues, and research findings on crankshaft hardness.

Identifier  ExFiles\Box 115\4\  scan0085
Date  18th June 1940 guessed
  
(2)

Under conditions of normal civil use we would not have had time to sort the whole job out, but it was with War Department contracts in view that we felt it incumbent upon ourselves to take some immediate action to protect the position should this erratic behaviour become more marked, and have alternative bearing materials in being.

As the result of our discussion in the Engine Shop during your visit threw rather a different light upon the problem as far as the writer is concerned, and a careful survey of the position would appear to indicate that temporary cessation of oil has caused the breakdown of certain bearings under service conditions. There is no question that a copious supply of oil to a bearing must at all times be beneficial, and when Mr. Howlett was at the Works he raised the question as to whether we had not been sufficiently generous in our bearing clearances, both axial and diametral, to ensure that this copious supply of oil was maintained under all conditions.

You asked in your letter why I should make the statement that copper-lead bearings were not so susceptible to shortage of oil as A.C. 9. I can only reply that as the result of service testing with a considerable quantity of copper-lead bearings we have not yet had returned any one bearing which has shown 'picking-up' due to apparent shortage of oil. I have also been advised that on a competitive engine copper-lead bearings have given the utmost satisfaction, and that bearing troubles had been eliminated by their use in conjunction with a cast iron crankcase, and running on a nickel chrome shaft with unhardened pins.

Further, as a result of our own testing in Research Department it was indicated that a certain hardness figure should be arrived at where a satisfactory combination of materials could be assured, and although admittedly the hardened crankshaft must be beneficial in any combination of bearing material, from a service angle it would appear that unless A.C.9 can run on a crankshaft pin to an equivalent hardness to that obtained on an ordinary nickel chrome or carbon steel shaft, there is a danger that an operator will re-grind until the hardness figure has been reduced, which would not provide consistent good running with A.C. 9 material.

With regard to RR.56, I admitted to both yourself and Mr. Howlett that we have had isolated bearing failures during the whole of the time we have been running on this material, but when we had the solid Duralumin connecting rod, as far as my knowledge goes, this trouble was practically unknown.
  
  


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