2001 Edition Yamaha F225A and LF225A Outboards Service Manual, Page 190Get this manual
Lower unit
11Add or remove shim(s) if out of specificationReverse gear backlash Less than 0.70 mm (0.028 in) More than 1.03 mm (0.041 in) M: Measurement Available shim thicknesses: 0.10, 0.12, 0.15, 0.18, 0.30, 0.40, and 0.50 mm 12Remove the special service tools, and then install the water pump assemblyShim thickness To be increased by (0.87 M) 0.71 To be decreased by (M 0.87) 0.71
8Remove the special service tools from the propeller shaft9Apply load to the reverse gear by installing the propeller 7, the spacer (without the washer 9), then the washer as shown