Yamaha Outboard Motors Factory Service Manual F6 and F8, Page 248Get this manual
THERMOSTAT, TIMING BELT AND GEARS Install: Timing belt Installing steps: (1)Turn the drive gear and align the washer groove on the drive gear and "" mark on the cylinder body (portin a)(2)Turn the driven gear and align the "1" mark on the driven gear and "" mark on the thermostat cover (portin b)(3)Install the timing belt 5
INSTALLING THE TIMING BELT