1981-1984 Official Honda ATC250R Shop Manual, Page 142Get this manual
r:::iJ HONDA BRAKE MECHANISM (FRONT DISC BRAKE) MASTER CYLINDER ASSEMBLY
Install the Oring in the groove in the reservoirClean the mating faces of the master cylinder body and reservoir and coat the surfaces with small amount of adhesive (THREEBOND No1211 or equivalent)Apply silicon grease to the piston cup and pour small amount of brake fluid into the cylinderNOTE Replace the master piston and spring as setDo not replace one without replacing the otherCheck that the snap ring is seated in the grooveInstall the front stoplight switchSEAL WASHERS