Harvester endless belt conveyors with floating idler rollers having belt tensioning mechanisms using compression springs disposed outside the conveyor housing side walls are show in U.S. Pat. Nos. 3,854,572; 3,804,231; and 2,302,656. U.S. Pat. Nos. 3,521,433 and 3,537,243 each show a pair of arms within an endless belt conveyor housing for supporting a conveyor idler roller for limited vertical swinging movement about a transverse horizontal axis. In these last-mentioned patents, the tensioning of the endless belt conveyor is effected in part by screw adjusters on the outside of the conveyor housing which are connected to pivot pins for the arms, which pivot pins extend through longitudinal slots in the side walls of the conveyor housing. Compression spring-type tensioning mechanisms for harvester conveyor idlers positioned on the laterally inner sides of the conveyor side walls are shown in U.S. Pat. No. 1,634,187 and 2,612,988.