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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).
Clarifying sizing and stamping conventions for Wraith pistons and cylinder blocks.

Identifier  ExFiles\Box 9\1\  01-page15
Date  14th June 1938
  
636.

To RHC{R. H. Coverley - Production Engineer}/SS.{S. Smith} from Rm{William Robotham - Chief Engineer}/Mths.{Reg Matthews}

Rm{William Robotham - Chief Engineer}/Mths.{Reg Matthews}4/MH.{M. Huckerby}14.6.38.

WRAITH PISTONS.

There is apparently some doubt as to the correct pistons to fit with various cylinder diameters. The procedure in the past has been to stamp cylinder blocks as "standard" as long as the diameter has been within the limits of the drawing; this means, of course, that a cylinder block may be stamped "standard" although it is .001 over the nominal size of 3.5005. With such bores it has been the custom in the past to fit standard size pistons.

In the case of a cylinder block stamped "plus 1" the bore may be from .001 to .002 over the nominal size and a .001 oversize piston should be fitted. [handwritten] Can be? ✓

Similarly, a cylinder stamped "plus 2" is actually .003 over the nominal size.

Rm{William Robotham - Chief Engineer}/Mths.{Reg Matthews}
  
  


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