Looking from the pilot seat the mags rotate counter clockwise (or anti clockwise) or to the Left. To advance the timing rotate the magneto housing in the direction of rotation (counter clockwise); to retard, roll it clockwise. With a buzz box it is easy to 'discover' this yourself. Even easier is to look at the Lycoming diagram, which I'll post as soon as I figure out how...There we go. Green arrow is advance, red is retard. I agree with others that simply rotating the magneto without some timing apparatus (buzz box) is a bad idea, but wanted to answer the question.
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==dave==
N102FM