South Bend 10K spindle adjustment needed?

On my SB 10K the leather belt runs true when the lathe is turned on. I notice when I start machining the belt moves about 1/8 of an inch. Always in the same direction. Is this normal, an indication of something wrong, or can an adjustment be made to stop the belt movement?
Thanks in advance, Marv Linke

It could be just the belt causing it. That the belt is stretched out to one side and tracks over when under load. Personally, you should get rid of that leather belt and spend the money to get one of the new belt kits with the ???? (some sort of plastic) backing. They let you use a lot more HP than the leather before it slips. You will be happy if you do.