Mount the mount plate (BVi1581) to the stand (Desvil).

Install the gearbox on the mounting plate (BVi1581) (fig. 1).

Installing the gearbox to the mounting plate

Remove the clutch release slave cylinder.

Clutch housing: 1 - clutch release bearing, 2 - clutch release slave cylinder, 3 - hydraulic fluid supply pipe

Unscrew the bolts located inside the crankcase (fig. 2).

Removing the rear cover

Remove the rear casing strictly along the horizontal axis of the box, as it includes a lubricant capsule located in the input shaft hole (Fig. 3).

Engaging first and fifth gear

Engage the first gear with the shift lever, and the fifth one by sliding its fork along the stem (Fig. 4).

Remove the output shaft bolt and remove the input shaft nut.

Using a punch (BVi31-01), knock out the fifth gear fork pin.

Removing the fifth gear fork pin

Remove the fifth gear fork and gear.

Remove the 5th gear hub using tool (BVi1170).

Removing the hub

Install the accessory gear (BVi1170) into fifth gear by turning it to align the splines of the gear and hub

Remove the fixture together with the hub (fig. 6)

Removing the fixed 5th gear

Remove the 5th gear fixed gear using tools (BVi22-01 and BVi1000) (fig. 7)

Remove the outer crankcase bolts.

Removing the speed sensor

Remove speed sensor B (for semi-automatic transmission JH1) (fig. 8)

Holes (C) to be covered

It is recommended to put two magnets or block holes C in order not to lose balls and springs for fixing rods 1/2 and 3/4 (Fig. 9)

Removing the stem and reverse contactor

Remove reverse stem A and reverse contactor B (fig. 10)

Press the shift rod outwards.

Removing the "Reverse 5th" shift fork stem

Disconnect and remove the crankcase.

Turn the reverse axle assembly to the left and remove the reverse/fifth shift fork stem (fig. 11)

Raise the input shaft slightly and remove the reverse gear axle assembly (Fig. 12)

Removing the reverse axle assembly

Disconnect the 3/4 yoke pins with the tool (BVi949) and remove the stem and yoke 3/4, input and output shaft assembly with stem and yoke (fig. 12)

Removing the stem and yoke assembly 3/4, 1/2

Simultaneously remove the input and output shaft assembly with the stem and yoke 1/2 (Fig. 13)

Removing the locking pins

Removing gears

Clamp the output shaft in a vise with jaws, and then remove all gears.

Removing the circlips

When removing and installing circlips, use circlip pliers on one side and pliers on the other (fig. 15).

Check Details

The teeth of gears and clutches should not be excessively worn or serrated.

Also, make sure that there are no signs of friction or excessive wear on the surfaces of the shafts and the inner surfaces of the gears.

It is recommended to mark the position of the gear couplings relative to the hubs.

Replacing bearings in the crankcase

Forcing the bearing into the crankcase

Spread the circlips with suitable pliers and press the bearing into the crankcase using tool (B.Vi1576) (fig. 16).

JH3 gearbox disassembly can be found in the article - "JH3 gearbox disassembly"