Mercury Mariner 30/40 4-Stroke Outboard Service Manual 1998, Page 470Get this manual
BIGFOOT GEAR HOUSING
10Install locating disc against bearing carrier shoulder in gear housing11 Position access hole as shown
aLocating DiscAccess Hole 12Determine pinion gear depth by inserting feeler gauge thru access hole in locating disc13The correct clearance between gauging block and pinion gear is 0.025 in(0.64 mm)14If clearance is correct, leave Bearing Preload Tool on drive shaft and proceed to mining Forward Gear Backlash ,H following15If clearance is incorrect, add (or subtract) shims from above bearing race to lower (or raise) pinion gearWhen reinstalling pinion nut, apply Loctite 271 on threads of nut