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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).
Technical memo discussing piston failure, its causes, and proposed design modifications.

Identifier  ExFiles\Box 180\M3\M3.2\  img018
Date  16th March 1925
  
TO H.S. } FROM R.{Sir Henry Royce}
SECRET
R1/M16.3.25.
E.{Mr Elliott - Chief Engineer} A.{Mr Adams} C.
PISTON FAILURE & SCRAPER RINGS. X8040

This is quite a reasonable failure due to high engine speeds and explosions causing concentrated alternating stresses at the end of the horizontal saw cut. How can these stresses be reduced?

My first idea was to drill a hole to finish the saw cut, then reinforce round the hole.

Another was to use two 1/4" fine thread bolts to reinforce the aluminium. These might bite into the piston pin at one or both ends. They could be used as a means of making the piston pin tight, but I should not recommend slotting (splitting) the boss.

Do we still use the diagonal webs? One thinks that we ought.

My impression is that the aluminium is OK. for compression due to the stresses caused by the explosions, but following these by the tension at high speeds at the end of the exhaust stroke is too much for the metal, and either the section or the metal is different in the die castings.

It would seem that some definite improvement should be made and the engine should be fitted with suitable

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