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Tech. Advice: Industrial Engines
V-Twin Magnetos
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<blockquote data-quote="Nigel Spaxman" data-source="post: 89999" data-attributes="member: 2907"><p>There is one thing about the behaviour of the V twin magnetos that is not quite symmetrical. It is the reason that one spark has to be after the maximum magnetic flux and not before. Even after the maximum magnetic flux has occurred the current in the coil tries to stay constant, because that is what coils do. The coil current continues even though it is not pushed by the flux because it is propelled by the magnetic properties of the coil. That is the reason the spark on the front cylinder can be reasonably strong even though the magneto is 25 degrees (magneto armature degrees) past the point of maximum magnetic flux. A spark timed 25 degrees before would be a lot weaker than the one 25 degrees after. But apparently some mags on 45 degree V twins are timed with one spark before and one after, but those would only be 11 1/4 degrees before and after maximum magnetic flux. Probably there would be a point that would be even better to get even sparks but that might vary with engine speed (maybe 5 degrees before and 16 1/4 degrees after) </p><p>This problem of timing the spark so it is synchronized with the maximum magnetic flux is also the reason why manual advance mags (the Lucas type ones) don't have as good a spark for starting as the auto advance type. The spark timing is altered by moving the cam ring which changes the timing of the spark relative to the armature poles. With the auto advance the points stay at the same relationship with the armature. Probably it is also the reason why some early V twins had twin mags.</p></blockquote><p></p>
[QUOTE="Nigel Spaxman, post: 89999, member: 2907"] There is one thing about the behaviour of the V twin magnetos that is not quite symmetrical. It is the reason that one spark has to be after the maximum magnetic flux and not before. Even after the maximum magnetic flux has occurred the current in the coil tries to stay constant, because that is what coils do. The coil current continues even though it is not pushed by the flux because it is propelled by the magnetic properties of the coil. That is the reason the spark on the front cylinder can be reasonably strong even though the magneto is 25 degrees (magneto armature degrees) past the point of maximum magnetic flux. A spark timed 25 degrees before would be a lot weaker than the one 25 degrees after. But apparently some mags on 45 degree V twins are timed with one spark before and one after, but those would only be 11 1/4 degrees before and after maximum magnetic flux. Probably there would be a point that would be even better to get even sparks but that might vary with engine speed (maybe 5 degrees before and 16 1/4 degrees after) This problem of timing the spark so it is synchronized with the maximum magnetic flux is also the reason why manual advance mags (the Lucas type ones) don't have as good a spark for starting as the auto advance type. The spark timing is altered by moving the cam ring which changes the timing of the spark relative to the armature poles. With the auto advance the points stay at the same relationship with the armature. Probably it is also the reason why some early V twins had twin mags. [/QUOTE]
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Tech. Advice: Industrial Engines
V-Twin Magnetos
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