To stabilize the damper operation of a chain tensioner by suppressing the wear of the valve seat of a check valve.
The chain tensioner 1 includes a plunger 10 slidably inserted into a cylinder 9 in the axial direction, a return spring 26 for energizing the plunger 10 in the protruding direction, an oil supply passage 13 provided in a pressure chamber 12 encircled by the cylinder 9 and the plunger 10 for introducing operating oil, and the check valve 14 provided at the end of the oil supply passage 13 on the side of the pressure chamber 12 for preventing the backflow of the operating oil, the check valve 14 consisting of the valve seat 16 having a valve hole 15, a check ball 17 for contacting/leaving the valve seat 16 to open/close the valve hole 15, and a retainer 18 for restricting the moving range of the check ball 17. A chromium diffusion layer 29 is provided on a contact face 28 of the valve seat 16 with the check ball 17.
SATO SEIJI
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Takayoshi Tagawa
Yaichiro Nakatani