Abstract: A tensioner mechanism adapted for placing tension in a drive belt of a mower deck, the tensioner including an elongate member operatively coupled with an idler arm, and slidably mounted with a support member operatively carried by the mower deck. A compression spring carried on the elongate member between the idler arm and the support member operatively presses the idler arm away from the support member and is completely compressed during normal mowing operations for generally blocking the idler arm from swinging toward the support member during operation. A threaded member within which said elongate member is slidably received is adjustably fixed with the support member by a pair of nuts that can be adjusted on the threaded member to alter the position of the threaded member with respect to the mower deck for adjusting the tension that the idler pulley places in the belt during normal mowing operations.