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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).
Load reduction through crank balancing, bearing fit, and heat treatment procedures.

Identifier  ExFiles\Box 116\1\  scan0051
Date  18th July 1938
  
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Rm{William Robotham - Chief Engineer}/CTS.{C. Trot Salt - Carburation}16/MH.{M. Huckerby}18.7.38.

If the crank was balanced it was stated that the load would be reduced by approx. 800 lbs./sq.in. This procedure, however, Dennis would adopt only as a last resource.

If the crank pins were drilled the loading would be reduced by approx. 200 lbs/sq.in.

The bearing is fitted into a cast iron crankcase with an interference fit of .003. There were signs of pinching due to lack of space for expansion, it was suggested, therefore, that the bearing should be made a "fit".

Heat Treatment.

The bearing in question had a heat treatment as follows:-

12 hours at 180°C followed by a second period of 12 hours at 180°C. The hardness was checked after the first period and found to be 55 Brinell. After the second period it was 62-64 Brinell.

In this condition, there was about .062 of metal to be removed by final machining and the point was raised whether the bearing ought to be further heat treated after rough machining and and prior to final boring.

It was decided therefore to try a bearing thus treated, together with the altered "fit" of the bearing in the c/case.

This constitutes the next test condition proposed to be carried out by Messrs. Dennis.

Rm{William Robotham - Chief Engineer}/CTS.{C. Trot Salt - Carburation}
  
  


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