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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).
Report page detailing the sparking range and characteristics of various magnetos, including Watford and Bosch models.

Identifier  WestWitteringFiles\I\July1922\  Scan127
Date  31th July 1922
  
Contd. -9- EPCL/T31.7.22.
34°, which amount of range is that required for our engine.This applies in the case of most magnetos, in which the best retarded position requires to be as advanced as possible). as better low speed sparking is obtained the greater the advance over this portion of the range).

On sleeve type magnetos, however, this does not apply , and it may even be that the selection of the 34° range from the more retarded portion of the available range will give the better low speed sparking characteristic in the retarded position of the lever.

On the Watford EO.6c magneto the makers range is only 33° and the advance and retard is limited by the movable sleeves, so that the makers fully retarded position was used in the comparison.

On the M.L.O.6 magneto the advance and retard is still limited by movable sleeves attached to the cam ring; the range provided being 62°, a selection of 34° had to be made. It was found that better retard low speed sparking results were obtained by selecting the more retarded portion of this range, so that our retarded position agreed with the makers, whereas our advanced position was 28° less advanced than the makers.

(15) High Speed Sparking Characteristics.

U.S.A.Bosch ZR.6. The maximum regular sparking gap lengths at all speeds from 1100 to 3400 R.P.M. for the three positions of the timing lever were:-

Advanced 4.5 mm.
Central 7.5 mm.
Retarded 7.5 mm.
Contd.
  
  


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