Crawls Backward (When Alarmed): 1931 Martin 0-18T Guitar Restoration and Repair, Pt. 1

I've had this Martin 0-18T (tenor) guitar hanging around The Dungeon for a couple of years. I'm trying to play tenor guitar more, so I figured it was about time I took a look at what it needs to be playable.

The top is so yellowed and dark that I kept thinking it was a Style 17 (mahogany top, back and sides). But no, it's really a Style 18 - spruce top and mahogany body. The lacquer has just turned a dark amber.

Plus it's really dirty.

Headstock is filthy. Plus we have rusty strings and corroded tuning machines. Note the greenish tinge. Disgusting.

Hopefully I can clean all this up.

There are quite a few scratches, but none are that bad. And I don't see any cracks.

My guess is it was stored in a semi-dry, but still somewhat humid basement, hence the corrosion on the tuners. And the humidity actually prevented cracks.

The back seam may have opened up a bit, but I can't get it to budge. There is, of course, a bracing strip along the back on the inside, so it's held together tightly.

It may be that the seam opened and what we see here is dirt that's gotten in. I'll know more as I clean it.

In any event, I'm not worrying about the integrity of the joint. It's solid.

Did I mention it's really dirty?

I took a weak mixture of Simple Green and wiped it down. I'll clean and polish it later, but I wanted to at least get the surface dirt off while I work on it.

The guitar needs three major repairs:

1 - a neck reset (pretty typical for an old Martin).
2- the neck has a bad backbow and needs to be straightened (more on that later).
3- a refret. I probably could salvage the original frets, but I want to put in frets with a larger tang to help the backbow issue.

So I'm going to do the reset first, then tackle the neck/fret issues.

I need to take a couple of measurements to calculate how much to take off the heel during the reset.

With the guitar tuned to pitch (holding my breath with those grungy tuners and ancient strings), I measured the distance a straightedge placed on the frets falls under the top of the bridge. I used to do this with a small ruler, but a while back I sprung for this helpful gauge.

You get a direct readout of the distance instead of trying to eye tiny marks on a ruler. In this instance, the distance is .130 inches.

Then I use a top deflection gauge and set it to zero on the bridge with the guitar under tension.

With the tension removed (strings loosened or removed), I then measure this same point. The top will deflect a bit - in other words, it will move downward with no tension.

Depending on the guitar, the string gauge, etc., this distance could be substantial. In this instance, it was only 3 thousandths of an inch (.003). It's a small guitar, and only has 4 strings, so there isn't a lot of deflection (tension). But on a larger six-string guitar, the deflection would likely be higher.

Why is this important? Well, the gauge is not totally necessary, but it helps us get a much more accurate angle on the neck after the heel is cut and the neck is reinstalled. If we were able to raise the top of the guitar up to the exact height it would be under string tension without the strings on it, we'd be simulating that tension and thus be able to judge the exact correct angle for the neck!

Again, .003 is such a tiny amount that this may not be worth worrying about, but I may as well raise the top anyway, in the name of accuracy.

I have a brace jack that I've mounted to a piece of scrap wood. I've found the jack tends to dance all around the inside of the guitar otherwise, so this keeps it in place while we put it in position.

The piece of wood can span a couple of back braces inside the guitar, and the jack can be positioned right under the bridge where we measured the deflection.

We can use a mirror to see the position of the jack, and then raise it. Just a couple turns does it. Then we measure the deflection again with the gauge (I didn't take a picture but it's just the same way we measured it above), and adjust the jack until we've raised the top that measly .003 inches.

Now the top of the guitar is at the same height it would be if it was strung to pitch.

While we're inside the body, we can take a look at the model number and serial number on the neck block.

The serial number indicates it was made in 1931.

Martin has kept meticulous records. If you write them, they can generally provide the day the instrument left the factory!

Try that with a Gibson or Guild.

Those tuners were really bothering me, so I decided to go ahead and take them off and clean them up.

They came off easily, except for one which just wouldn't come out of its bushing. So I put some PB Blaster between the tuner's shaft and the bushing. It took a day of small applications of Blaster to get the tuner to come out.

Dunked the tuners in naptha to drive all the old dried-up lubricant out of them. That also took a lot of the crud and corrosion off.

Then I sparingly applied some Tri-Flow lubricant to the proper places, and turned them to work the Tri-Flow in.

They were all originally very stiff, but now they turn easily.

Finally I polished them with Mother's Mag Wheel polish. They look much much better.

Unfortunately, there is some pitting on the chrome buttons which can't be removed. But at least they work well and just look like old tuners instead of being green and corroded.

With the tuners off the guitar, I took the opportunity to clean and polish the headstock, since it's more accessible with the tuners removed.

What a difference, huh? Compare this to the picture above. I have high hopes for the rest of the finish now.

You can see one bushing came off. I have since reinstalled it with a couple drops of thin CA.

Next, we'll measure for the reset and get the neck off.

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