A snowblower belt drive system a tensioner pulley that can slide forwardly and rearwardly in a path that is substantially parallel to an endless drive belt between a drive pulley and a driven pulley. A drive belt engagement spring urges the tensioner pulley rearwardly along the slot to engage the drive pulley and driven pulley. A manual return spring urges the tensioner pulley forwardly along the slot to disengage the drive pulley and driven pulley.