Yamaha 115-225 HP Outboards Service Manual, Page 165Get this manual
Forward gear shim 1) Find forward gear shim thickness (T2) by selecting shims until the specified measurement (M) with the special tool is obtainedSpecified Measurement (M)1.10 mm-R100 mm
If the value is negative (-), then add the value
2) is the deviation of the lower case dimension from standardIt is stamped on the trim tab mounting surface of the lower case in 0.01 mm unitsIf the mark is missing or unreadable, assume an mark of "0", and check the backlash when the unit is assembledExample: If mark is "+5", then =1.10-(+5Y1oo mm1.10-0.05 mm1.05 mm (0.041 in) If mark is "-3", then1.10-( -3)100 mm1.10+0.03 mm1.13 mm (0.044 in) 3) Place the original shims on the thrust washer (mounted between the bearing and the gear) and place the shimming gauge on top of the shims as shown in the illustration