If you are talking about the stop motion knob in the center of the hand wheel, the problem is probably that someone has cranked it down too tight to keep it from coming loose as they sewed.
Tri-Flow or other good penetrating oil. Heat from a hair drier, and a large jawed set of channel lock pliers with a piece of leather around the knob. It might take 4 hands too. Two for the pliers, two for the hand wheel.
I've had them that tight and they are hard to get off.
Once off a thorough cleaning followed by oiling and proper assembly of the clutch washer under the stop motion knob should fix the problem.
Joe
Last edited by QuiltnNan; 01-03-2016 at 10:42 AM.
Reason: language