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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).
Ignition plug failures from sooty deposits and the potential of a jump spark distributor.

Identifier  ExFiles\Box 34\2\  Scan101
Date  14th May 1918
  
To EH. from R.{Sir Henry Royce}
c. to CJ.
c. to EFC.

X.2514
14th May. 1918.
R21/G14.5.18.

X2514 RE IGNITION PLUGS.
X.2514.
X.3199.
X.3299.

Recently you wrote me on the subject of ignition plugs in which you found that certain sooty deposit was a cause of failure of certain types of ignition plugs. I should be glad if you would let me know if the jump spark distributor which acts as an external gap can be proved to be a definite advantage from this point of view, and also if Mr. Clark can determine what loss in the length of the spark is caused by the introduction of another very short gap.

It appears from our car experience that the jump spark distributor does not demand the coil to give a longer spark to obtain an ewually reliable ignition. We know, however, that it must have some resistance, but what effect for certain, we have no means of telling. The usual jump spark need only have a clearance of, say, .010", and can have metal points which will not oxidise, such as Tantalum.

R.{Sir Henry Royce}
  
  


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