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Lycoming Internal magneto timing


Active member
I have a GO 435 and am having trouble with the internal timing of the mags(S 20 series mags). When I took them apart I found them timed differently. One was set on CC boost and one was CW normal. My question is since they are clockwise driven mags and have a counterclockwise distributor should they both be set to CCW or CC. Can somebody get me pointed in the right direction on this. I have no trouble getting them timed back to the engine ... just stumped on the internal timing. Also should they be set to normal or boost as well? Any existing threads on this?

Does one have an impulse coupling on it and the other doesn't?

I think that would make them set up different, but could be wrong.
They should be set to the direction the mag shaft rotates--facing the mag. The points cam can be turned over for clock wise or counter clock wise rotation as a side note. The cams are usually marked with arrows.
Rotate the engine in the direction of rotation to determine the mag rotation direction and set the internal timing accordingly. Most Lycommings have left hand rotating mags if memory serves me well.
From what I was told, you can set them both the same(normal). And you won;t have any problems. My GPU is set that way and it runs great. I have rebuilt probably 6 units and I set the notched tooth to the keyway and it works every time. When you set the notched or colored tooth in the center of the hole, you should feel tension from the magnet.
I was also told if you set it to boost it changes the amont of degrees your timing cahnges with less mag mag movement. Don't quote me........ I drink...

P.S. Be sure to clean the contacs under that plastic gear, its actually a distributor cap and rotor, so to speak.
Direction of mag shaft rotation was what I thought . Thanks guys for the help. I love this website!