Check the condition of the front coupling dogs of the gears. They must be in perfect condition and with no sign of wear on the edges of the teeth.
The idler gears must rotate freely on their shafts.
When refitting, make sure the circlips are correctly positioned.
Check the needle roller bearings for wear.
The threads and splines of the shafts must be in perfect condition.
Also check that the component parts of the gear selector mechanism are in good condition.
Engage

Engage the gears and check that the gearchange mechanism does not stick (selector fork - gear groove, and fork pin - desmodromic drum groove) due to incorrect end float. Restore the correct end float by shimming the gearbox shafts and the selector drum with suitable shims.
For the total gearbox shaft and selector drum end clearance values, refer to sect. 3 - 1.1, Gearbox.
Disassembly of the gearbox shafts
Inspection of the gear selector forksRefitting the starter motor gear
Position the washer (20) and the gear (19) in the pin (21) and take the pin
into contact with the crankcase half.
...
Removal of the movable tensioner/timing belt
Loosen the nut (8) and remove the washer (7) and the tensioner pulley (9)
from the pin (12) on the cylinder head.
Remove the timing belt (14) from the horizontal cylinder assembly.
Important
If the belts are to be re-used, mark the direction of rotation with an
arrow and also mark the cylin ...
Refitting the hands free
Reassembly is a reversal of the removal procedure: in particular apply
prescribed threadlocker to screws (2) and tighten
them to a torque of 20 nm +/- 10% (sect. 3 - 3, Frame torque settings).
If the hands free button has been previously removed, when refitting it insert
the spring (6) on pi ...