Don't know that the hammer block has anything to do with it. As haifabuddy mentions there is a good chance the mainspring is the problem and is stubbing into the hammer. The mainspring looks entirely too straight, there should be more arch to it. Make sure the strain screw is tight and see if it goes away.

Both the symptom you describe and the appearance of the mainspring point to this.

The strain screw is not an adjustment! It is supposed to be tight at all times. A loose strain screw is the most common cause of malfunctions of all types in a Smith revolver.