A knife arm assembly for connecting a sickle knife to a reciprocating drive mechanism (62A, 62B), comprising: a knife arm having a mounting end configured for attachment to the drive mechanism (62A, 62B) for reciprocating sideward movement therewith, a distal end opposite the mounting end disposed to be supported in cantilever relation to the drive mechanism (62A, 62B), the distal end having an inner surface bounding and defining a cavity and a first opening at a first end of the cavity, the first opening and the cavity having a substantially uniform first transverse extent, and a bearing element retained in and occupying a substantial portion of the cavity, the bearing element having an inner bearing surface bounding and defining a receptacle therein and including an open end generally proximate to the first opening, configured for cooperatively receiving a knife pin of a knife head of a sickle for relative rotation of the knife arm and the knife head; characterized by the knife arm having a shoulder extending at least partially about and defining a second opening at a second end of the cavity opposite the first end, and the second opening having a second transverse extent smaller than the first transverse extent, and a plug disposed in the second end of the cavity, the plug having a third transverse extent marginally smaller than the first transverse extent but larger than the second transverse extent so as to cover the second opening while being restrained from passage therethrough by the shoulder, and the plug being configured to be forceably movable toward the first end of the cavity and against the bearing element for pressing the bearing element from the cavity through the first opening. a knife arm having a mounting end configured for attachment to the drive mechanism (62A, 62B) for reciprocating sideward movement therewith, a distal end opposite the mounting end disposed to be supported in cantilever relation to the drive mechanism (62A, 62B), the distal end having an inner surface bounding and defining a cavity and a first opening at a first end of the cavity, the first opening and the cavity having a substantially uniform first transverse extent, and a bearing element retained in and occupying a substantial portion of the cavity, the bearing element having an inner bearing surface bounding and defining a receptacle therein and including an open end generally proximate to the first opening, configured for cooperatively receiving a knife pin of a knife head of a sickle for relative rotation of the knife arm and the knife head; characterized by the knife arm having a shoulder extending at least partially about and defining a second opening at a second end of the cavity opposite the first end, and the second opening having a second transverse extent smaller than the first transverse extent, and a plug disposed in the second end of the cavity, the plug having a third transverse extent marginally smaller than the first transverse extent but larger than the second transverse extent so as to cover the second opening while being restrained from passage therethrough by the shoulder, and the plug being configured to be forceably movable toward the first end of the cavity and against the bearing element for pressing the bearing element from the cavity through the first opening.