Described embodiments include a reconfigurable belt tensioner that can be used to add, remove, and/or reposition peripheral accessories of an engine installation, for example, in an automobile or another vehicle. The tensioner has a housing, an arm with an axle, and a spring installed in the housing. The axle is inserted into and fastened to the housing. The arm rotates around the axle. When the arm is rotated, the spring provides the force that tends to return the arm and the housing to the original position. The tensioner can be reconfigured by repositioning the spring relative to the housing and/or the arm, changing the angle between the housing and the arm. The tensioner may be used, for example, on an LS-based GM small-block engine, and allow operation with and without the air conditioning compressor or other accessories.