Yamaha 25BMH 30HMH Factory Service Manual, Page 326Get this manual
BACKLASH
E (3) Install the backlash indicator onto the drive shaft (16mm (0.63 in) diameter)Backlash indicator 90890-06706 (4) Install the dial gauge onto the lower unit and have the dial gauge plunger contact the mark on the backlash indicatorMagnet base plate 90890-07003 Dial gauge set 90890-01252 Magnet base 90890-06705 (5) Slowly turn the drive shaft clockwise and counterclockwiseWhen the drive shaft stops in each direction, measure the backlash2Adjust: Forward gear backlash Remove or add shim(s)Forward gear Shim thickness backlash Less than To be decreased by 0.31 mm (0.012 in) (0.52M) 0.49 More than To be increased by 0.72 mm (0.028 in) (M0.52) 0.49 Available shim thickness: 1.0, 1.1, 1.2, 1.3 and 1.4 mmMeasurement