How can I reset the timing on my Singer 9224 sewing machine?

My Singer 9224 sewing machine needs the timing reset. I have had this adjustment made by a repair person in the past, but they have moved and there is nobody else in the area. This machine needs constant adjustments, and it is time I learned to do this myself. I have removed and then tightened the needle bar and have tightened the cogs on the underside of the machine. The situation is somewhat improved, but the machine still will not form a stitch. The upper and lower stitches will not lock together. Please help.