A conveyor chain drive unit having a main frame formed essentially by an H-section structural member whose flanges provide a pair of vertical plates located on either side of the path of travel of the conveyor chain. A bearing mounted on one of these plates supports the vertically extending output shaft of a reducer with the reducer housing positioned above the main frame. Connected to the reducer housing is a movable frame which extends radially outward from the axis of the reducer output shaft and supports a motor for driving the reducer. The conveyor chain is engaged by a caterpillar type of drive chain trained about a drive sprocket on the reducer output shaft and about a take-up sprocket and a back-up bar both mounted on the one side plate of the main frame. A roller nest carried by the opposite main frame side plate holds the conveyor chain in engagement with the drive chain. The movable frame pivots about the axis of the reducer output shaft in response to the driving torque thereon; and this pivotal movement is restrained by a compression spring and shock absorber. Excess pivotal movement is sensed as an overload condition.