1991 Yamaha Outboard Factory Service Manual 9.9 and 15 HP, Page 96Get this manual
4 Place the gear case in an inverted position and install it on the repair standI nstall the dial gauge on the dial gauge stand and install it on the gear caseInstall the backlash inidcator rod on the drive shaft; and bring the dial gauge stem into contact with the "30A" on the indicator rod
5Slowly turn the drive in and out, and read the dial gauge when the drive shaft stops in each directionDetermine the shim size according to the following chartThickness of shims to be added or removed Measurement is less than specification: (0.46measure ment)thickness of shims to be removed (Measurement 0.46)thickness of shims to be added