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 the standard allowances for fitting pistons to prevent knocks, with different specifications for various materials.
| Identifier | Morton\M11\ img203 | |
| Date | 1st August 1919 | |
| To from R.{Sir Henry Royce} Copy to C.U. " " H.V. " " E.P. " " HON. " " EPC. D ORIGINAL SEP 1919 RECEIVED RE PISTONS X. 2748 R6/G27/8/19. (2) I would like it to be thoroughly understood that I have never recommended the fitting of pistons tighter than our usual standard allowances with the object of preventing piston knocks. These allowances are difficult to describe in a letter as they vary with different parts of the piston, and different types of pistons. Generally speaking, however, it is an average of .004" or .005" clear for cast iron or steel, and double this amount for aluminium. for a 4 1/2" dia. Piston. R.{Sir Henry Royce} | ||