There is a spring and a rod assembly. There seems to be different size washers, Shoulder bolts and lock washers. There are torque specs that should be adhered to. Also I don't see any adjustment for the tension pulley but the belt guard has adjustment.Here are some instructions. Parts Link is at the bottom.
2. From bag of parts, position idler sheave (A) and belt guide (B) onto tiller tensioning arm (C). Make sure shoulder (D) on sheave is seated against the belt guide.
3. Install M8 x 1.25 x 50 mm flange bolt (E) from bottom side of tensioning arm. Install M8 x 1.25 lock nut on top side of sheave finger tight only.
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I hope you know how to copy and paste. If you need anything else feel free to ask.