2009 Yamaha F40 Outboard Service Manual, Page 272Get this manual
Shimming
Shimming
Before selecting the forward gear shim(s) (T1) and reverse gear shim(s) (T2), make sure to select the pinion shim(s) (T3) When assembling the lower unit to measure the backlash after selecting the pinion shim(s) (T3), do not apply gear oil, grease, or sealant to the parts When assembling the lower unit after shimming is completed, make sure to apply gear oil, grease, or sealant to the specified areas