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.

Use generator cover or a service cover with puller part no. 88713.1749 fitted to it. Secure cover to casing with some of the original screws and begin separation by turning the central pin of the tool.

Remove gearbox shafts and gearbox selector drum from the casing (Sect. N 7.2, Gearbox assembly: gearbox shafts).

Remove timing layshaft (17) and take O-ring (25) in the oil duct between casings.

Check bearings (1) and (18) for wear. Note that the main bearings must always be changed in pairs (see procedure in “Main bearings”, next paragraph).

When replacing gearbox shafts bearings (19) and (9), secure them in place in the casings using the spacers (2) and the stop plate (10).

Change the oil seal (8) placed outside the bearing (9) every time casings are overhauled.

Do not damage the shim (6) between the bearing (7) at gearbox primary shaft end and the casing on chain side.

The main bearings have offset inner races so that the balls can transmit the loads from one groove to the other along straight lines at a particular angle to bearing axis. The angle-contact ball bearings are designed for bearing combined loading (radial-axial loads).

They may bear axial loading in one direction only. Because of radial loading, the bearing produces an axial force that must be combined with an opposite force and it is thus usually fitted in opposition to another.

On badly worn engines, bearing bushes may have developed clearance in the casing - normally, bushes are interference-fit in the casing.

Check that casing to bushing interference, with bearings (1) and (18) installed, is not below 0.03 mm; if not so, change the casings.

Carefully inspect the casings. They should be in perfect conditions and clean. Mating surfaces must be perfectly flat and free from burrs.

Measure the depths "LA1" and "LA2" corresponding to the distance between the mating surfaces of the two casings and the contact surfaces of the inner races of the bearings;

Add a pre-load of 0.30 mm. This will compensate the additional end float resulting from heat expansion when casings reach operating temperature;

This gives:
SA=LA1+LA2+0.30-LA.

SA=SA1+SA2
where "SA1" and "SA2" represent the shimming for the clutch-side casing 1 and chain-side casing 2.

Install a shim of min. thickness (1.90 mm) on each side of the crankshaft to avoid contact between crank web and engine block.

Fit four M8 screws into the holes shown in the figure and tighten to the specified torque (Sect. C 3, Engine torque settings).

Note dial gauge reading. This will be crankshaft end float. Add pre-load (0.30 mm) and total size of shims used (1.90x2=3.8 mm).

Measure “LP” and “LS” on the primary and secondary shafts (for secondary shaft, also add shim thickness “R” of 2.3 mm).

Measure the depth corresponding to the distance between the contact surface between the casings and the contact surface of the inner race of primary shaft bearing "CP1" and "CP2" and of the secondary shaft bearing "CS1" and "CS2".

Considering that end float should be 0.05 - 0.20 mm, and taking the average optimal value of 0.15 mm, this gives:

SP=CP1+CP2-LP-0.15 and
SS=CS1+CS2-LS-0.15.

SP=SP1+SP2 and
SS=SS1+SS2

Where “SP1” and “SP2” represent the primary shaft shimming on the clutch side and chain side and “SS1” and “SS2” represent the corresponding secondary shaft shimming. This gives:

SP1=CP1-64-0.075 and
SS1=CS1-64-0.075 and therefore
SP2=SP-SP1 and SS2=SS-SS1.

Considering that end float should be 0.10 - 0.40 mm

and taking the average optimal value of 0.25 mm,

hence ST1=LT1-59-0.125 and so
ST2=ST-ST1.

Place a dial gauge (T) with magnetic base on a support plate fixed to crankcase. Bring stylus in contact with selector drum end and set dial gauge to zero with the stylus touching the drum. Lever drum and note dial gauge reading. This will be total end float. Consider that the final end float should be between 0.10 and 0.40 mm, determine the amount of shimming required.

Now hold the primary shaft in position and check that the clutch dogs of the sliding gear are equally distant from the dogs of the fixed gears. This is done by inserting a feeler gauge (S) between the dogs.

Fit a 2.5-mm shim (H) to the secondary shaft.

Determine the amount of shimming for the left end (generator side) to obtain nearly zero end float when the casing is closed.

Place a small shim (1.5 mm) on primary shaft and no shims on the secondary shaft.

Final play must be between 0.05 and 0.20 mm for both shafts.

Play should be closer to 0.05 rather than 0.20 mm.

Install and adjust the gear selector lever assembly (M) (see Sect. N 7.1, Reassembling the gear selector lever).

Place gearbox in NEUTRAL and look through the opening of the horizontal cylinder to check that the clutch dogs of the sliding gears are equally distant from the fixed gear dogs (Fig. 1 - Fig. 2).

Insert the forks of the 1st-4th and 2nd-3rd gears (D) into the grooves of the secondary shaft driven gears.

Insert the fork of the 5th-6th gears (E) into the primary shaft driven gear.

Make sure that the connecting rods (H) are correctly positioned in the cylinders. Incorrect positioning will inevitably lead to reopening of the casing.

Make sure that the two centring bushes (22) are fitted.

Thoroughly grease the O-ring (31) and place it close to the oil duct connecting the two casings.

To prevent damage to the oil seal (14) on the timing layshaft, insert a protection cap part no. 88713.5749 on the shaft threaded end. Dampen the oil seal (14) with alcohol and fit it on the timing layshaft. Drive it fully home on the roller bearing (4).

When refitting used components, make sure that the inner races (C) of the gearbox shaft end bearings are fitted into the correct bearing and are not on the shaft.

Match the casings (3) and (13). Tap the area around the shafts with a plastic hammer, if necessary.

Grease the jointing screws with recommended grease and start them into their holes on the generator-side casing. The screws are not all the same length, be sure to position them correctly.

Tighten all screws to the specified torque (Sect. C 3, Engine torque settings). Begin with the larger diameter screws.

Check that crankshaft rotates with a certain amount of interference in the main bearings. Crankshaft must have a pre-load of 0.20-0.30 mm. Check also that all assembled parts can rotate or move correctly.

Fit the cartridge filter as described under Sect. D 4, Changing the engine oil and filter cartridge.

Fit oil seal (8) and spacer with O-ring on gearbox secondary shaft as described under Sect. G 8, Replacing the gearbox secondary shaft seal.