OK here's the scenario. I bought a lovely guitar from a guy for peanuts. This guy needed money, I low-balled, he snatched my hand off. Guitar was supposedly set-up by a pro. Sure enough it was lovely. Action was perfect. But it was tuned an octave high!!! Of course once I retuned the strings came down on the frets. I slacked off the trussrod (single action) until it came completely loose and there's still not enough relief. Is there any hope? Or have I bought a decoration?
What kind of strings was he using to get an octive up? I'm guessing they must have been picolo strings or some other very light gauge. If that's the case get some new strings of your liking and redo the setup.
That's the problem, though. It won't set-up. What I think went on it that the trussrod had to be cranked up so tight to keep against the string tension (regular medium guage) that it may have permanently deformed the neck. In any event the rod is completely backed off to the point that it is slack and there is still no relief.
Sometimes careful 'manipulation' physically is needed to get the neck to do what you want. If you do some searching on line, you should be able to find some resources about 'forcing' some bow (or removing it in some cases) into the neck. I wouldn't suggest it in very many cases, but as a last resort, when you get to 'last' you might look into it.
Sometimes a good repairman can either put the neck on a heat press and re-warp it or in an extreme case defret the fingerboard, level it and refret it. I had to have Bruce Sconzert of Longhorn Guitars in Ft. Worth do that to my Series I Alembic, but I'm not sure it's worth the effort if it's a cheapie. Is it a bolt-on? What about a replacement neck?
Guitar? Not a bass? An octave up? I don't think strings like that exist. Frankly you could try tuning your guitar high for a bit with no tension on the truss rod to force the neck back into shape. Applying heat (with a lamp) would help the process. BTW Strings tuned up an octave are at double the frequency and hence 4 times the tension. The strings would DEFINITELY break. Alternatively, if you were using thinner strings at the same tension, they would need to be half as thin. Your high E would be on the order of .005 inch. And it would not exert extra tension on the neck. EDIT: Re-read your post. Regular medium gauge will definitely not tune an octave up. EDIT2: Definitely need to know what kind of instrument we're dealing with. Acoustic guitar? Electric guitar? Bass? What strings were on it - Brand and Gauge?
Give it time. The neck may relax on it's own if you wait a bit. Don't do anything to it for a week or two.
It's a Beaver Creek acoustic bass. Strung with D'addario mediums. It was an octave high. The owner must have been out to lunch. I agree, though, that it's incredible that the strings didn't bust. Thanks for all the great suggestions BTW.
I once watched a Fender employee running a setup clinic at our local music store lay the neck of a nasty old bolt neck electric across a bench block near the headstock and push down hard enough in the middle that it produced an audible crack. He fiddled with the truss rod adjustment for another minute, then put a fresh set of strings on the guitar and completed the setup. When it was my turn to have him set up my bass, I asked him about cracking that neck. He said sometimes a truss rod gets jammed from being left at one extreme or the other for so long it's stuck, and what he did was the best way he had found to get it unstuck.
I'd be more worried about top damage having strung the bass to 4x normal tension. With normal bass strings you're talking about roughly 700-800lb of tension on the neck, top and truss rod. Running it in my head, there's really no way it could have been octave up. It's like driving a car over 4 acoustic basses (one under each wheel) and hoping that they don't explode. D'addario must make at least 10 different types of string. What kind and what gauge? Is it possible the owner used acoustic strings instead of bass ones?