Be gentle: don’t use an impact wrench!
If the shaft fractures and separates during an alternator replacement, this can usually be attributed to improper mounting. When replacing an alternator (type MG), you should therefore pay very close attention to the following points.
Sometimes, it is necessary to fit the belt pulley from the old alternator onto the new alternator. If that is the case, on no account tighten the nut with an impact driver—otherwise, the shaft may fracture. However, if there is not enough tightening torque applied to the nut, this may cause serious damage to the alternator, since the inside ring of the roller bearing is braced against the shaft by means of the pulley nut.
No stress: no contact between rotor and stator
Without the correct prestressing, the shaft wears quickly and ultimately begins to wobble. The rotor and stator can thus come into contact, eventually causing a short circuit and therefore the complete failure of the alternator.
M16 x 1.5: 95 Nm (±5 Nm)
M27 x 1.5: 152 Nm (±17.5 Nm)
Align correctly to keep the right spacing
If reusing the old belt pulley, first check it thoroughly for damage and wear. When mounting the belt pulley, it is important to ensure it is in the correct position. You can customize the alignment using the washers.