1998-2006 Yamaha F20/F25 Outboards Service Manual, Page 243Get this manual
SHIMMING (FOR USA AND CANADA)
SHIMMING NOTE:
There is no need to select shims when reassembling with the original case and inner parts Shim calculations are required when reassembling with the original inner parts and new case (the difference between the original inner parts and the new case) Measurements and adjustments are required when replacing any inner parts
SHIM SELECTION (FOR USA AND CANADA)
Pinion gear shim