Make the rear wheel turn until you find the position where chain is tightest. Set the vehicle on the side stand. Push down the chain at the point of measurement and release. Measure the distance between the "aperture" upper profile and pin centre.
The read distance must be: 9 to 11 mm.

Important
If the drive chain is too tight or too slack, adjust it so that tension reading will fall within specified range.
To adjust the tension remove the rear splash guard (sect. 7 - 13, Removal of the swingarm).
Slacken off the two clamp screws (1) that secure the rear wheel hub to the swingarm.
Fit the hook spanner code 88713.1038 Inserting its tooth in the eccentric hub (2).
Rotate the eccentric hub (2) to obtain the correct chain tension.
Turn counter clockwise to tighten the chain; clockwise to loosen (from chain side).
Important
An incorrectly tensioned chain will lead to accelerated wear of the transmission components.
If the screws (1) are removed, lubricate with specified grease underhead and thread, then tighten the screws (1) to the torque of 35 nm +/- 5% (sect. 3 - 3, Frame torque settings) proceeding with sequence 1-2-1.

Warning
The correct tightening of the fixing screws of the eccentric hub is essential for the safety of the rider and the passenger (sect. 3 - 3, Frame torque settings).
Refit the rear splash guard (sect. 7 - 13, Refitting the swingarm).
Adjusting the steering head bearings
Checking brake pad wear and changing brake padsRefitting the evaporative emissions canister
To refit, carry out the removal operations in reverse order, making sure to
locate the hoses as shown in the figures at the
end of the chapter.
Positioning the hoses / clamps and canister filter
...
Removing of the cylinder head pulley/fixed tensioner
Insert the tool code 88713.1806 In the pulleys to lock their rotation and use
the bush supplied to loosen the fixing nuts
(21) of the pulleys.
important
On reassembly, always use new nuts.
Remove the nuts (21) and the pulleys (11) from the camshafts.
Loosen the nut (8), and remove the was ...
Refitting the rear mudguard
Place the rear mudguard (8) on the swingarm, fitting the screws (9) with
recommended threadlocker.
The screw (9) in the bottom hole of the rear mudguard (8) must be installed with
the washer (r).
Tighten the screws (9) to a torque of 5 nm +/- 10% (sect. 3 - 3, Frame torque
settings).
...