1998-2006 Yamaha F20/F25 Outboards Service Manual, Page 253Get this manual
SHIMMING (FOR USA AND CANADA)
Example: If "R" is "+5", then:1.0(+5)100 mm1.0-0.05 mm.95 mm (0.0374 in) If "R" is "-3", then:1.0(-3)100 mm1.00.03 mm1.03 mm (0.0406 in) Install: Needle bearing Oil seal (onto the propeller shaft housing) Refer to "Propeller shaft housing assyassembly"
3Set: Shimming gauge (onto the reverse gear shim ball bearing as shown)