2001 Mercury Mariner 50-60HP Factory Service Manual, Page 443Get this manual
NON-BIGFOOT GEAR HOUSING
7The correct clearance between the gauging surface and the pinion gear is .025 in(0.64mm)8If clearance is more than .025 in(0.64mm) remove shims from under the upper bearing cupIf clearance is less than 0.25add shims under the upper bearing race9After final adjustment to pinion height, and forward gear backlash has been established, apply Loctite 271 to threads and torque new pinion nut to specified torque