A tensioning device for an endless traction element in an engine. The tensioning device has a housing, a plunger, which can he moved in the housing, a compression spring arranged in the plunger, a nonreturn valve arranged between the plunger and the housing, a cylinder arranged in the plunger, and an engagement element. The plunger and the cylinder are connected to one another by a latching system via engagement of the engagement element, and the cylinder is connected materially to the nonreturn valve.