Nates Corner Let's say the crack won't come together with masking tape alone. You could try a long spool clamp (you can buy running thread from the hardware store) and make them any length you need. Or you might have a cam clamp to clamp the entire body. Use discretion and care or you might split the sides as well. Then you all Jam up.
What if you can clamp the crack shut but one side's up and one's down? Then you need a way to clamp a cleat on to that crack from the inside every inch or so. Don Teeter in his book, The Acoustic Guitar has a great device for that. Most cracks can be fixed this way without having to disassemble the instrument. And the only telltale scar will be an orthoscopic stringhole (use an old guitar string of .012" or less).
Here's how: work the string through by wiggling, rotating, or other
means of getting through the back,side, or top . Keep feeding it in until you can pull it out of the soundhole. In lei-making fashion string up the pre-drilled cleat and lock the end on to a bead or anything that will lock the end. Glue up the face of cleat that will go against the crack. Pull on the string until the cleat touches down. From the outside, string up into the jig and start winding. Not too tight or you may snap the cleat. Let the glue dry, unwind jig, and pull out the string from the inside. This is the tricky part since you can't get your fat hand through the soundhole. I use a
stiff wire with a tight hook on the end to snag the string ball. E-mail me
on your ideas for getting out the string