A telescoping belt tightener for conveyors includes an elongated outer body and a slider tube inserted in one end, with the slider tube able to slide into and out of the outer body to varying lengths. An adjuster at an opposing end can be turned to extend or retract the slider tube from the outer body. A bearing collar, with a bearing cavity that fits a spherical bearing, is attached to the slider tube. A collar shield snugly fits with the bearing collar to keep contaminants from entering the bearing cavity. One or both ends of the outer body include a stopper for keeping contaminants from entering the outer body. The outer body is round and without standing surfaces on which food and debris could accumulate. The outer body and adjuster are unitary parts without crevices in which contaminants can collect. The belt tightener is well-suited for food-grade applications.