A belt tensioner includes an arm, a spring case, and a helical spring having inwardly projecting first and second end portions. Another belt tensioner includes a spring, an arm, a spring case, and a pivot bushing surrounding the spring. An additional belt tensioner includes an idler pulley having a bearing with a mounting hole and includes an arm having a post. The post is positioned in the mounting hole, and an annular rim of the post is deformed radially outward and over the bearing. A method for manufacturing an arm and a spring case of a belt-tensioner includes obtaining a belt-tensioner-arm casting mold including a first section and a second section and obtaining a belt-tensioner-spring-case casting mold including a first segment and a second segment.