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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).
Modifications to the 25 HP crankshaft to improve high-speed smoothness.

Identifier  ExFiles\Box 103\3\  scan0072
Date  4th August 1931
  
To E.{Mr Elliott - Chief Engineer} from Hs{Lord Ernest Hives - Chair}/Gry.{Shadwell Grylls}

85010.

Hs{Lord Ernest Hives - Chair}/Gry{Shadwell Grylls} 2/AM.4.8.31.

25 HP. CRANKSHAFT.

One of the means which we have found for getting high speed smoothness is to balance both the crankshaft and the big end. We did this on the 25 HP. 2" pin crankshaft. The top torsional period began to be felt at 3750 R.P.M. which speed we anticipate reaching shortly on the road. If we could raise the fringe of the period by 200 R.P.M. the car should then be smooth under all conditions.

We are submitting a sketch of the stiffest crankshaft we think can be made from the existing forging and fit the existing crankcase. Will you let us know whether you consider it worth while making a shaft to these dimensions.

We should have liked to increase the journals to 2.500 dia. but find that no increase can be made without using thinner white metal (now .050) or steel shells (present thickness .125) because of the position of the studs in the crankcase. Would you agree to recessing the shell in order to miss the stud? We could then add about .200 on the journal diameter.

Hs{Lord Ernest Hives - Chair}/Gry.{Shadwell Grylls}
  
  


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