Bold reference numbers in this section identify parts shown in this exploded view diagram. These parts do not appear in the figures near the text.

Pull out the fork selector drum (16). Pay attention to the shims (31) and (27) fitted on the shaft, make sure to refit them to their original position.

Now you can replace the needle roller stop ring (32) and the special needle rollers (33).

Remove the gear selector forks (29) and (28).

If the bearing inner rings (A) remained on the shafts, slide them out of the gearbox primary (2) and secondary (25) shafts (Sect. N 9.2, Main bearings).

Remove the clutch-side shim (26) and the chain-side shim (15) from secondary shaft.

Remove the driven gear for the 4th speed (21), its needle roller cage (4) and the safety washer (12).

Remove the driven gear for the 3rd speed (22), its needle roller cage (4) and the safety washer (6).

Remove the circlip (7) and remove the driven gear for the 6th speed (23).

Remove the circlip (7), the safety washer (6) and the driven gear for the 2nd speed (24).

Remove chain-side shim (11) and clutch-side shim (1) from primary shaft.

Slide out the 2nd drive gear (10). Using two screwdrivers, remove circlip (7) and safety washer (6).

Check the condition of the needle roller cage (13) and of the oil seal (14) on top of the gearbox primary shaft. If needed, remove them with a suitable puller and replace.

Engage the gears and check that the gearbox control does not jam (selector fork-gear groove and fork pin - desmodromic drum groove) due to incorrect end float. Correct clearances by shimming the gearbox shafts and drum with suitable shims.

For total end float of gearbox shafts and selector drums, refer to Sect. C 1.1, Gearbox.

Visually inspect the gear selector forks. Bent forks must be changed as they may lead to difficulties in gear changing or may suddenly disengage under load.

If it exceeds the service limit, establish whether it is necessary to change the gear or the fork by referring to the limits specified for each part (Sect. C 1.1, Gearbox).

If the service limit is exceeded, establish which part must be changed, by comparing the values with the values of new components (Sect. C 1.1, Gearbox).

Fig. 1 shows all parts to be fitted onto the primary shaft (2), after calculating correct thickness for shims (1) and (11) (Sect. N 9.2, Shimming the shafts).

Fig. 2 shows all parts to be fitted onto the secondary shaft (25), after calculating correct thickness for shims (15) and (26) (Sect. N 9.2, Shimming the shafts).

Special care must be taken when fitting idle gears. Installation of 3rd and 4th gears and all fasteners onto the secondary shaft is here shown by way of example.

Fit the gear for 3rd speed (22).

Fit the gear for 4th speed (21).

To reassemble gearbox components, follow the procedure under Section
N 9.2 "Closing the casings" relating to the engine casings reassembly.

When finished, run a practical test. Place gear in neutral and check that the front coupling dogs (A) of the sliding gears (B) are centred to the matching dogs of the fixed gears (C), i.e. that the distance is the same at both ends.

Engage a gear and make also sure there is always a small clearance between fork (D) and matching groove (E) in the sliding gear (B).