1998-2006 Yamaha F20/F25 Outboards Service Manual, Page 265Get this manual
ISHIMMING (EXCEPT FOR USA AND CANADA) 3Select: Reverse gear shim(s) Calculated numeral More than 1.00 1.10 1.20 1.30 or less than 1.10 1.20 1.30 1.32 Shim size to use 1.0 1.1 1.2 1.3
Available shim thickness: 1.0, 1.1, 1.2, and 1.3 mm
BACKLASH MEASUREMENT
Do not install the water pump compo nents when measuring the backlash Measure both the forward and reverse gear backlashes If both the forward and reverse gear backlashes are larger than specificationthe pinion gear may be too high If both the forward and reverse gear backlashes are smaller than specification, the pinion gear may be too low If either of these conditions exist, then check the pinion gear shim(s) selection