YAMAHA Marine 100A Manuel D'entretien page 470

LOWR
BACKLASH (REGULAR ROTATION MODELS)
2. Adjust:
• Reverse gear shim
Remove or add shim(s).
Reverse gear
backlash
Less than
0.80 mm (0.031 in)
More than
1.17 mm (0.046 in)
M: Measurement
6-73
E
Shim thickness
To be increased by
(0.99 – M) × 0.63
To be decreased by
(M – 0.99) × 0.63