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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).
Specifying the clearances and fits for 4¼ Litre Bentley main bearings.

Identifier  ExFiles\Box 115\3\  scan0115
Date  19th November 1937
  
1020

To RHC.{R. H. Coverley - Production Engineer} from Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell}
c. By.{R.W. Bailey - Chief Engineer}

4¼ LITRE BENTLEY MAIN BEARINGS.

In reply to your memo RHC{R. H. Coverley - Production Engineer}/2/MJ.19.11.37 regarding a definite decision for clearances with which to assemble engines with white metal thrust bearings and the remaining bearings in Hall's AC.7 alloy, we give herewith the necessary figures for the job.

WHITE METAL REAR THRUST BEARINGS.

To be in accordance with the half drawings EB.791 and EB.614 as standard on 30 HP, with exception of the following limits etc.

(a) End thrust clearance to be .002 normal and .003 maximum.

(b) Working clearance to be .0025 normal with a minimum of .00225 and a maximum of .003.

(c) White metal faced steel shims as standard 30 HP.

REMAINING AC.7 MAIN BEARINGS.

Interference fit, nip and working clearance to be in accordance with latest Bentley drawings EB.3331 and EB.3334 which in figures are -

(a) "Interference fit"
Is the amount the outside diameter of the bearings is in excess of the diameter of the crankcase and cap housing into which it fits. To normal dimensions this is .001 and with extreme limits, size and size.

(b) "Nip".
Is the amount the bearing halves stand proud of the joint face.
This should be .001 at each side of the bearing relative to the joint face on both halves.
  
  


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