Yamaha Marine Outboards Factory Service / Repair/ Workshop Manual 225G 250B L250B, Page 224Get this manual
BACKLASH (COUNTER ROTATION MODELS)
(3) Install the backlash indicator onto the drive shaft (on the 22.4 mm (0.88 in) diameter portion of the drive shaft)Backlash indicator YB-0626590890-06706 (4) Install the dial gauge onto the lower unit and have the dial gauge plunger contact the mark on the backlash indicatorMagnetic-base plate6 YB-0700390890-07003 Dial gauge set YU-0309790890-01252 Magnetic base8 YU-3448190890-06705 (5) Set the lower unit upside down(6) Slowly turn the drive shaft clockwise and counterclockwiseWhen the drive shaft stops in each direction, measure the backlash2Adjust: Forward gear shim Remove or add shim(s)Forward Shim thickness gear backlash Less than 0.32 mm (0.013 in) More than 0.52 mm (0.020 in) M: Measurement To be increased by (0.42 M) 0.78 To be decreased by (M 0.42) 0.78