The steering head bolt can go as tight as you like, subject to any recommended torque settings by Yamaha.

Initially you should tighten the nut that sits over the top race (with the dust cover in between, of course) to a level where you can feel resistance in trying to turn the handlebars. Slacken off a smidge from there so that the handlebars move freely.

When you come to tighten the steering head bolt, I would hold the previously referred to nut in place with a C spanner and then tighten to spec, if there is one. Handlebars should move freely without any knocking or graunching.