Yamaha F100B F100C Outboards Factory Service Manual, Page 204Get this manual
Lower unit
6Add or remove shims if out of specificationForward gear backlash Less than 0.13 mm (0.005 in) More than 0.47 mm (0.019 in) M: Measurement Available shim thicknesses: 0.10, 0.12, 0.15, 0.18, 0.30, 0.40, and 0.50 mm 7Remove the special service tools, and then install the water pump assemblyShim thickness To be decreased by (0.30 M) 0.56 To be increased by (M 0.30) 0.56
4Install the backlash indicator onto the drive shaft (20 mm [0.79 in] in diameter), then the dial gauge onto the lower unit