Re: F-4 Magneto Question

Posted by Dave Allgire on February 18, 2007 at 08:53:23 from (71.85.239.227):

In Reply to: Re: F-4 Magneto Question posted by Roger Mills on February 18, 2007 at 07:18:30:

A little long winded, maybe. The F-4 magneto is capable of a 35 degree spark range. To properly set the timing you first must set the points to .013". With the mag off of the engine, or backed away from the coupling, insert a nail to lift the pawl off of the impulse coupling. Then rotate the spark lever housing up as far as it will go. This grounds out the points. Remove the cover and rotate the mag until the breaker arm rubbing block is on any high point of the cam. Set the points to .013". A slight drag on the feeler guage indicates the correct setting. Now remove the distributor cap and rotate the mag so the distributor disc is in the 2 o'clock position. This should line it up with the brush for the #1 plug. Next insure the timing mark on the flywheel indicates #1 and that #1 piston is at top dead center. Without disturbing the mag settings you have just made, try installing the mag back on the engine. If the coupling does not line up, remove the two capscrews in the coupling plate, rotate the plate until it lines up and reinsert the capscrews. To check the timing, crank the engine over 4 full turns until you are coming back up on #1 cylinder. The timing mark on the flywheel should be in the window, the distributor disc should be in the 2 o'clock position for the #1 plug, if everything is correct. If the timing is correct, remove the nail that is holding the impulse pawl off of the impulse coupling. If timing is not correct, make the necessary adjustments to the coupling plate with the two capscrews. This plate is made such that only two holes will line up in any position. Now as you crank the engine over, you will hear the impulse coupling "click" for each plug in the firing order. And the timing mark may or may not be exactly in the center of the window. Ideally, you want the impulse to click just after the piston has passed TDC. That way you insure the piston will be headed in a downward direction. That could be as much as 8 degrees past TDC. Keeps the engine from kicking back and breaking things, like your arm, wrist, etc. Hope this helps and answers your questions. I got this info from an F-12 service manual, the Blue Ribbon Service manual on magnetos and my own experience. If you have more specific questions, my EMail is open.

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