In a spring-loaded tensioner lever having a coiled torsion spring accommodated in a space inside the lever, a stopper mechanism, comprising a pin held removably in a hole in the lever, holds an arm of the torsion spring against movement in the unwinding direction while the lever, or the chain, is being mounted on a mounting surface. The pin and a bent end of the arm of the spring fit into holes in the mounting surface positioned so that a pivot shaft-receiving hole of the lever is automatically aligned with a shaft-mounting hole in the mounting surface.