A tensioner that includes a piston supported slidably in a piston bore
formed in a housing, a piston spring biasing the piston in the protruding
direction, and a circlip member having an expandable ring-shaped body
that is engageable with the rack teeth of the piston. In the piston bore,
the ring-shaped body of the circlip member is adapted to engage with an
upper and lower stop surface. The rack teeth of the piston are formed in
such a shape that when the ring-shaped body of the circlip member engages
with the upper stop surface of the piston bore, the piston is permitted
to move in the protruding direction and, when the ring-shaped body of the
circlip member engages with the lower stop surface of the piston bore,
the piston restricts movement in the retracting direction.