In one aspect, the invention is directed to a belt tensioner for tensioning a belt, comprising a pivot shaft that is fixedly mountable with respect to an engine block of an engine, a tensioner arm rotatably mounted to the pivot shaft for pivoting about a tensioner arm axis in a first direction and in an opposing second direction, a pulley rotatably mounted to the tensioner arm for rotation about a pulley axis, and a tensioner spring positioned to bias the tensioner arm in the first direction, wherein the tensioner spring has a first end and a second end, wherein the first end is engaged with the tensioner arm, and a micro adjustment mechanism that is operatively connected to control the position of the second end of the tensioner spring so as to control the tension in the tensioner spring.