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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).
Potential causes and tests for piston knocking issues.

Identifier  ExFiles\Box 148\3\  scan0049
Date  21th February 1928 guessed
  
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(3) Is the trouble from tilting of the piston due to dry or tight patches on the skirt? All aluminum pistons are cleared away so much at the ring "lands" and are so flexible in the skirt that there is strong feeling in the "trade" in Detroit (where the Bohn "Nelson-strut" pistons are universal) that the knocking is due to what they call "tumbling" of the pistons in the bore.

DORRIS
now comes forward with the piston shown in attached folder (toNa.) in which one of the rings is held central by a steel plate, which is a few thousandths smaller than the inside of the ring, thus giving a rigidly piloted piston more like the cast iron designs.

We want to try this scheme in an engine, which already knocks, as it is a design which appears to overcome one of the chief disadvantages of the al. piston. (We know that in extreme cases we see marks of "tumbling" in the bore.)

(4) Out of round bores can be left out of the discussion as if this were the trouble it would be worst on 2 and 5, whereas it is worst on 3 and 4.

(5) It may be due to distribution being not good enough with American fuel (similar to early experience on the S. Ghost) so that the oil in the bores of 3 and 4 is continually washed off by liquid fuel.

But 2 and 3 and 4 and 5 have siamesed intakes, so that it is difficult to see how distribution could particularly affect 3 and 4.

(6) Do 3 and 4 cylinder bores run colder than the others due to water inlet being opposite them? I think we can prove this point on MX{John H Maddocks - Chief Proving Officer}-3 with water inlet to the head.

Items 1, 3, and 6 above are all in line for testing before the cold weather is over.

I recommend that we should carefully examine the results from the point of view of forming a correct idea of the cause.

Meanwhile will Maintenance give us all possible assistance by finding exactly the conditions under which piston knocking has occurred in the depots, and what has been done to affect a cure.

MO r/

OY
Maurice Olley
  
  


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