A bearing assembly includes a bearing (10) having a bearing surface (16) defining a bearing hole (12) therein and a shaft (20) disposed in the bearing hole of the bearing. The bearing has an open end for the shaft insertion therethrough into the bearing hole along an axial direction of the bearing. The shaft defines a notch (24) in an outer periphery thereof, which is located corresponding to the open end of the bearing. A plurality of spiral grooves (228) are defined in the outer periphery of the shaft above the notch. A rotation direction of the shaft is the same as a spiral direction of the grooves during rotation of the shaft. A cover (50) covers the open end of the bearing and closely surrounds the grooves of the shaft.