Posted by Janicholson on August 30, 2010 at 18:46:21 from (67.72.98.45):
In Reply to: h mipulse rotor posted by PeteEllis on August 30, 2010 at 11:48:12:
I have a little more time now, so here goes. The impulse coupling is designed to trip at TDC. This process initiates earlier in the rotation with a pawl that catches and holds back a spring. The spring winds up for a given number of degrees of rotation. When it trips, the rotor is not pointing to the spark plug terminal. it is leading the terminal slightly. The tripped magnetic rotor spins up to speed making current flow in the primary mag winding. When the current is flowing at max, the points open. This occurs a little after TDC, making sure that there is no chance for kickback if the engine was hand cranked. This breaks the current, and a secondary voltage is generated in the spark windings. This voltage is directed by the rotor to the appropriate spark plug terminal (it is now lined up directly toward that terminal.) When the engine starts, the mag impulse coupling is removed from action by a governor (speed sensor) that pulls in the pawl, preventing spring windup. This also causes the spark to no longer have the delay caused by the impulse system. Thus the spark timing is at full running advance. IH mags of this type have no centrifugal advance. I hope this explains a lot. The timing of the rotor is best set by timing marks on the little gears. Jim
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