Overhauling the main bearings
Remove the engine from the frame (Removing the engine).
Remove the timing outer covers (Removing the timing outer covers).
Remove the timing belts (Removing the tensioner pulley/timing belt).
Remove the timing layshaft pulleys (Removing the timing layshaft pulleys).
Remove the complete cylinder head unit (Removing the engine heads).
Remove the cylinder/piston assembly (Removing the cylinder/piston assembly).
Remove the generator side cover (Removing the generator cover) and the complete generator (Removing the flywheel/generator unit).
Remove the starter motor (Removing the starter motor).
Remove the clutch cover (Removing the clutch cover).
Remove the clutch unit (Removing the clutch).
Remove the oil pump (Removing the oil pump).
Remove the primary drive gear (Removing the primary drive gear).
Remove the mesh filter (Changing engine oil and filter cartridge).
Separate the crankcase halves (Separating the crankcase halves).
The main bearings (14) and (15) have offset inner races so that the balls transmit loads from one groove to the other along straight lines at a certain angle to the bearing axis.
The angle-contact ball bearings are designed for bearing combined loading (radial-axial loads).
Bearings of this type can bear direct axial 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.
To replace the bearings proceed as follows:
-
heat the crankcase in an oven to 100 °C;
-
remove the bearing using a drift and hammer;
-
install the new bearing (while the crankcase is still hot) keeping it perfectly square in its seat using a tubular drift that only bears on the outer ring of the bearing;
-
allow the parts to cool and check that the bearing is securely seated in the crankcase half.
Crankcase half (P) contact surface.
Important
On worn engines, the bearing holder bushes may no longer be tight fitted in the crankcase halves.
Check that the interference fit between the crankcase and the bearings (14) and (15) installed, is not less than 0.03 mm, otherwise, replace the crankcase halves.
Important
After installing new main bearings, shim the crankshaft and close the crankcase.