The main bearings have are of the angular contact type with offset inner races so that the balls transmit loads from one groove to the other along straight lines at an angle to the axis of the bearing. The angle-contact ball bearings are designed for bearing combined loading (radial-axial loads).
Bearings of this type can bear thrust loads in one direction only. In fact, under the action of a radial load inside the bearing, an axial force is created that must be counterbalanced by an axial force acting in the opposite direction; that is Why these bearings are generally fitted back to back in pairs.
Note
The main bearings supplied can be bearings with bushing (a) or flanged bearings (b) with the bushing integrated in the external ring of the bearing.
To renew the bearings proceed as follows:
Bearings with bushing
Important
On worn engines, the bearing holder may no longer be a tight fit in the crankcase half.
After having removed the bushing, check that the interference fit between the crankcase and the bushing, with bearing fitted, is no less than 0.03 Mm, otherwise, replace the crankcase halves.
Note
Fit the bearings (1) and (18) orienting them so that the side with the "letter" (c) is facing the bushings (2) and (17).
Flanged bearings
Important
On badly worn engines, bearing outer rings may have developed clearance in the crankcase halves - normally, bearing outer rings are interference-fit in the casing.
Check that the interference fit between the crankcase and the bearings (1) and (18) installed, is not less than 0.03 Mm, otherwise, replace the crankcase halves.
Important
After installing new main bearings, shim the crankshaft as described in the paragraph "shimming the shafts" and "reassembly of the crankcase halves" of this section.
Removing outer components
Note
The following removal operations are required in order to renew and/or
clean the crankcase halves. If the original
crankcase halves are to be reused, then the removal of these components is not
essential.
Unscrew the screw (17) and remove the oil breather valve (1) with the o-rings
...
Removal of the cylinder heads
Using the tool code 88713.2676, Undo the nuts (21) on the cylinder head stud
bolts.
Remove the cylinder head nuts (21) and special washers (22).
Remove the cylinder head assembly by lifting it off the engine studs.
Repeat the same procedure for the other cylinder head. ...
Replacing of the rear sprocket
Lock the wheel axle rotation.
Remove the clip (1).
Loosen the locking nut (2) with a socket wrench.
Fully unscrew the nut (2) and remove the washer (3) and the flange (5) with the
sprocket (17).
Collect the spacer (9).
Using a mallet, tap the flange (5) with the cush drive dampe ...