Carol,
>Remove the stop motion knob by loosing the little screw just till the knob will rotate, then take it off.
>Check the stop motion clutch washer. The two center fingers should face out towards the knob. I mark mine with a sharpie to make sure I get it back in the same way it came out. But if your having trouble that might not work.
>Remove the hand wheel and clean the main shaft and bore on the wheel.
>Clean the washer, and the stop motion knob.
>When reassembling the hand wheel I put one drop of oil on outer end of the shaft and slide the wheel on.
>Then the washer with the center fingers pointing out.
>Then screw on the knob all the way and tighten it.
>Tighten the little screw.
>If the screw hits one of the outer fingers of the washer, remove the knob and rotate the washer 180° or ½ turn. Then put the knob back on and tighten the little screw.
>If the knob goes on, but will not loosen, remove the knob and rotate the washer 180° or ½ turn. Then put the knob back on and tighten the little screw.
This should take care of the stop motion knob loosening up. When this has happened to my machines I've always found them oily and greasy.
Joe