The best and safest way is to load a dud roll into the 67, or try two empty spools loaded. A slender penny-sized tool is used to tweak the winding mechanism to allow 'dry firing', however, Pentax has never been too keen on dry firing: the camera was not designed for it; that is to say, it will only cock the shutter and initiate the winding mechanism when film is loaded. It is also too easy to damage the shutter curtain or mar the mirror. And old roll of film in it will be a much safer way to examine things.
Originally Posted by markbau