A chain tensioner comprising a housing, a plunger having racks formed on its opposite sides, a protrusion biasing spring, cams arranged in oblique guide grooves in the housing and engageable with the racks of the plunger, and a spacer supporting a cam biasing spring. The minimum backlash distance X is equal to h/tan , where h is the height of the rack teeth, and is the angle of the cam guide surfaces relative to the protruding direction of the plunger. The angle is between 15 and 70. The tensioner prevents wobbling noises produced by a timing chain on starting an engine, prevents whistling sounds due to excess tensioning of the chain, and allows backlash to be readily set to accommodate the requirements of a wide variety of engines.