Yamaha 115-225 HP Outboards Service Manual, Page 156Get this manual
AS_S_E_M_B_LY AN_D A_DJ_U_S_TM_E_N_T_(_11_5_-_22_5_)_
Reverse gear
1) Install propeller on the propeller shaft, with the front side facing backward, fit the nut and tighten
2) While pulling down drive shaft fully, slowly turn the drive-shaft in and out, and read the dial-gauge when the drive-shaft stops in each direction
3) Determine the shim(s) to be added or removed according to the chartReverse gear backlash Shim thickness (mm) to be adjusted
Less than To be increased by 0.80 mm (0.031 in) (0.96measurement) 1.25 0.801.12 mm (0.0310.044 in) Acceptable