Gas contaminants generated from the grease of bearings operating in a magnetic disk device adhere to the magnetic head and causing stiction and magnetic head crash. Such bearings are typically spindle bearings and pivot bearings. In operation, heat is generated that causes the bearing grease to generate the gases. By heat treating the grease, slow evaporating substances of hydrocarbon compounds with carbons of C9 to C13 in the grease are reduced to not more than 0.001 wt. % of the grease. The grease can then be used to lubricate the bearings. The heat treatment is performed at a temperature of 60.degree. to 100.degree. C. at a pressure of 10.sup.-3 to 10.sup.-8 torr. The assembled, lubricated bearings can be heat treated separately from the magnetic disk device or the heat treatment can take place after the bearings have been assembled in the magnetic disk device.