Yamaha 115-225 HP Outboards Service Manual, Page 170Get this manual
4) Determine the thickness size according to the chartReverse gear backlash Shim thickness decreaseincrease
Thickness of shim to be Less than decrease (mm) 0.50 mm (0.020 in) (0.60measurement) 1.25
0.50-0.70 mm (0.0200.028 in)
Decrease or increase
will be unnecessary
Thickness of shim to be More than increase (mm) 0.70 mm (0.028 in) (measurement0.60) 1.25