2000-2005 Yamaha F40B Outboard Service Manual, Page 116Get this manual
1LOWER UNIT Filling steps (1) Place the outboard in an upright position(2) Insert the gear oil tube into the drain hole and slowly fill the gear oil until oil flows out of the check hole and no air bubbles are visible(3) Install the gear oil level check screw and then quickly install the gear oil drain screwGear oil level check screw Nm (0.7 m.kgf, 5.1 ft.lb) Gear oil drain screw Nm (0.7 m.kgf, 5.1 ft.lb)
CHECKING THE LOWER UNIT (FOR AIR LEAKS)
Check: Lower unit holding pressure Pressure drops Check the seals and componentsLower unit holding pressure 100 kPa (1.0 kgfcm2, 14.2 psi) Checking steps