A conveyor assembly has a continuous conveyor belt driven between a pair of spaced side frame members by a center drive assembly having a pair of spaced side plates connected to the side frame members. A drive roller arrangement is driven by a drive motor arrangement coupled to the drive roller arrangement to move the conveyor belt. A freely rotatable guide roller arrangement is slidably mounted between the side frame members and the side plates between an operating position in which the conveyor belt passes around the guide roller assembly before engaging the drive roller arrangement, and a cleaning position in which the guide roller arrangement is slidably removable away from the side frame members and the side plates and out of engagement with the conveyor belt. The guard structure is retained in the operating position by elongated retaining pins that are pushed into a frictional engagement with the side plates, the guide roller arrangement and the guard structure, and removed to the cleaning position by pulling the retaining pins out of the frictional engagement. Each of the guard structures includes a roller adjustment device that can be selectively operated to adjust the orientation of the guide roller assembly between the spaced side frame members of the conveyor assembly.