What if I unscrew the truss rod too far?
 

Trying to understand truss rods on my new Yamaha FG800 and AC1R. Both have a 4mm hex fitting near the bottom of the fingerboard.

1. Does that 4mm hex tool turn the rod, or a threaded nut that's on the rod?

2. Is unscrewing (loosening, turning counter-clockwise) going to hurt anything if I go too far? Or will I just have a detached nut in my hand, or a threaded rod that needs to be restarted in its fitting up near the headstock?

3. On the AC1R I get a lot of resistance going clockwise. I'm curious what's going on - something bottoming out? The relief is good at a bit under .010 inch.

Thanks, all!

Many modern guitars have two-way rods that adjust in both directions. On those type, the nut is not removable. Single action rods generally have a removable nut. If loosening the rod does not meet any resistance, you probably have a one-way rod. If a truss rod is hard to turn, I remove the nut and lubricate the threads and the bearing surface. That is not possible with a two-way rod.
There are two basic designs for a two-way rod. On one, the rod itself turns when you adjust, creating a push/pull on a second rod or beam on top of the adjusting rod. This push/pull is accomplished by using left-hand threads on one end, or by using a different thread pitch. This rod cannot be completely unscrewed, because it is restricted by the second rod. Another design features a captured nut fixing it to the second rod, which creates the push/pull action. Capturing the nut means it cannot be removed.

Yamaha's website has instructions for adjusting relief in both directions so the nut would be captive and not removable.

When you’re going clockwise, you’re tightening the road and flattening the neck. It’s a good idea to do the adjustment with the guitar flat on its back and with the neck supported towards the heel. Use your left hand to apply gentle downwards pressure at the nut-end of the neck, whilst holding the butt-end of the guitar down with your right elbow, and turn the adjustment wrench with your right hand. Sounds a complicated manœvre, but it’s surprisingly easy in practice.

By ‘helping’ the neck in the direction that tightening the truss rod is taking it, you will take some of the resistance away that you’re feeling when you turn the wrench.

The usual disclaimers apply......IMHO, YMMV etc.

I haven't found that website. Can you help, please?

Thanks to all who've answered.

You haven't been able to find usa.yamaha.com ????

https://usa.yamaha.com/support/faq/g...sses/4068.html

I had, but not that page. Thanks for the link!