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To change the bearings, proceed as follows:
- Heat the crankcase half in an oven at a temperature of 100°C/212°F;
- Remove the bearing using a drift and a hammer.
- Fit the new bearing (while the crankcase half is still hot) perfectly in square with the axis of the seat, using a tubular pad which only applies the pressure on the outer ring of the bearing;
- let it cool and ensure that the bearing is securely fitted to the crankcase half.
After fitting the main bearings, proceed as follows to determine the total thickness "S" of the shimming:
- Measure "A" between the support surfaces of the bearings on the crankshaft;
- Measure the depths "P1" and "P2" corresponding to the distance between the contact surface between the crankcase halves (1 and 2) and the support surface of the inner raceway of the bearings;
- add a pre-load of 0.15 mm to allow for settling of the new bearings;
- this gives: S=P1+P2+0.15-A.
- To calculate the amount of a single shim, note that: S=S1+S2
- where "S1" and "S2" represent the shimming for the crankcase halves 1 and 2.
- Bearing in mind the shaft alignment, this gives: S1=Р1+0.075-A/2;
- and, finally, the second shim: S2=S-S1.
Note. After closing the crankcase half, it must be possible to turn the crankshaft with interference in the new bearings.