Evaluating a used Martin (or any other) guitar.

Discussion in 'Acoustic Heaven' started by Freeman Keller, Jun 18, 2021.

  1. Freeman Keller

    Freeman Keller Poster Extraordinaire

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    We have had a number of threads and discussions lately that involve buying or selling older guitars, and several on recent Martins needing neck resets. Lots of threads asking “what guitar should I buy for (insert price)” which get the inevitable answer “buy a used yyyy”.

    That can be great advice if the buyer knows how to evaluate a used guitar – what to look for and more important, what it costs to fix.

    A bit of serendipity came my way – a friend of a friend asked if I would take a look at a couple of his guitars. I approach every guitar that crosses my work bench in exactly the same fashion, and it’s the same way I would evaluate something I was considering buying. I thought it might be interesting to document the process with a few photos – I really don’t know what I’m going to find but it should be interesting.

    The guitars are a 2004 HD-28, that would be a typical “modern” Martin that might show up on CraigsList or a newspaper ad. One of them is a 1970 0-18, a typical post war Martin that might even turn up at an estate sale. I thought I would add my 1974 D-18 as a typical guitar from that low period of Martin’s past – there are lots of these that show up and they can be a real mixed bag. Much of what I do pertains to any used guitar from the 60’s or 70’s or early 2000’s – I approach them all the same way.

    There are a couple of things that are more or less unique to older Martins, I’ll try to point them out. There may also be exceptions to things I say here – this is meant to be a general approach to evaluation acoustic guitars.

    I probably won’t discuss how to fix the things we see, at least not in detail. I also won’t talk about the cost of these repairs – there are some price lists on repair tech forums, but often repairs costs depend on the actual instrument.

    Because of the limitations of forum software I’ll have to break this up into sections – that’s OK since each of these is really a separate topic. Have some patience with me as I write these, the answer you are seeking might be in the next post.

    It is also necessary to list my “credentials”. I am an amateur hobbyist builder. I’ve built 30 guitars of various types, many acoustics. I am also a hobby repair person – I like working on old guitars and several of the local musicians bring theirs to me for setups and various little fixes. I sit at the feet of great builders and repair people at GAL meetings and learn from every one of them. But it is important to note that I am not a professional and I most certainly am not an Authorized Martin technician.

    So, here are the three hombres – 2004 HD-28 back right, 1974 D-18, left, and 1970 0-18 on the bench.

    IMG_6748.JPG

    I’m going to add a link to two of the best articles about evaluating old Martins. Bryan Kimsey is one of the true experts on these guitars, he did the neck resets and other work on both of mine.

    http://www.bryankimsey.com/70s_D28/index.htm

    http://www.bryankimsey.com/problems/index.htm

    I am not going to link it directly but if you search around on Bryan’s site you will find his price list. I believe it is out of date but it gives a rough idea of what some of these operations will cost. Add 50 percent to be safe and you have some numbers for negotiation or budgeting.

    Oh, and one more thing before we get started. I am not going to try to discuss or evaluate tone, whether 70’s guitars were “overbuilt” (and what to do about it), the advantages of forward or backward shifting and all of that stuff. You can play the guitar and decide if is sounds good or bad – this discussion will be about the condition of the guitar, not how it sounds.
     
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  2. Fretting out

    Fretting out Doctor of Teleocity Platinum Supporter

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    Delete
     
    Last edited: Jun 18, 2021
  3. Freeman Keller

    Freeman Keller Poster Extraordinaire

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    HUMIDITY The very first thing I always check it the relative dryness of the guitar. I know a lot of folks poo poo this but its important for several reasons. The wood was dried for a long time to stabilize it and the guitar was built in a relative humidity of 40 to 45 percent. It would be very happy to spend the rest of its life at that humidity.

    If wood continues to dry it shrinks, that can lead to cracks. To counter this a slight dome is built into the top, our “flat top” guitars are not flat on top. As the top wood dries it shrinks across the grain the dome gradually settles out. Normally the slight movement of the top is tolerable – it drops a little in the winter when our houses are dry, comes back up in the summer. If it drops too low for too long it can split, often down the center seam.

    A dry guitar exhibits some other symptoms – the fretboard shrinks and the frets don’t so the ends get sharp. The finish can get wonkly looking. The action drops and the guitar might get buzzy. Humidity is always the first thing I check and if I feel it is too dry I postpone any work.

    The tests are very easy. Run your fingers down the edge of the fretboard – if the frets are sharp the board is dry. Lay a straight edge across the lower bout just behind the bridge – it should rock back and forth on the domed center, there should be a gap at the binding. Here is the HD-28

    IMG_6718.JPG

    It is dry. The top hasn’t cracked (yet) but its definitely not healthy. Here is the D-18, notice the nice dome and gaps at the sides

    IMG_6740.JPG

    And the 0-18 is somewhere in between. Over the years it has gone thru a lot of cycles, I think it is stable and just fine.

    IMG_6740.JPG

    My feeling is that the whole humidity thing is very important on a relatively new guitar and there are certainly some models that seem a lot more sensitive. Martins not as much, Taylors very. This is a Taylor that got a little too dry

    IMG_3623.JPG

    IMG_3622.JPG

    As I said, the herringbone is dry and before anything is done we need to get it stabilized at “normal” humidity level. I dampen a big car wash sponge and put it in a baggie with a bunch holes punched in it, and put it inside the guitar. Put it in its case for a couple of weeks, I redampened the sponge a couple of times.

    IMG_6755.JPG

    The guitar has mostly returned to its domed configuration, this is much better

    IMG_6753.JPG

    Before I leave humidity, as I said above a dry guitar has some other symptoms – sharp fret ends being one. Rehydrating will not fix this, if you have sharp frets plan on some dressing.
     
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  4. Freeman Keller

    Freeman Keller Poster Extraordinaire

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    NECK ANGLE

    Every acoustic guitar has an ideal geometry that lets you set the action to be as playable as possible AND impart the maximum amount of energy to the top. We can have long discussions about why this all works, but I’m going to make a simple statement here – on most guitars, including almost every Martin, if the fret plane just hits the top of the bridge or is slightly above the bridge the action can be adjusted to be playable. To shorten that a bit, if a straightedge laying on the frets just touches or is a bit above the top of the bridge then the neck angle is acceptable.

    There is another way to look at that, you need a certain height of saddle to drive the top – most people consider a bridge height of about 3/8 inch to be ideal and about 1/8 more of saddle sticking out. The second part of this consideration is whatever string height is acceptable to that player. To combine these thoughts – IF you have acceptable action AND 1/8 inch of saddle sticking out THEN the neck angle is acceptable.

    Both of those tests assumes that the guitar is properly hydrated – remember that if it is dry the top goes down which lowers the action, the neck will look like it is over set (above the bridge). Here are the guitars

    HD-28 (after humidifying), the straight edge is a hair below the top of the bridge. The action is playable at 0.080 to 0.110 but the saddle is only 0.060 or so above the bridge so it really can’t be lowered much.. The guitar is playable now but marginal, at some point in the next few years it will need a neck reset.

    IMG_6720.JPG

    D-18, the straight edge is a bit above the bridge, the action is a sweet 0.060 to 0.080, there is 0.130 of saddle sticking out. Hint, this guitar has had its neck reset, life is very good

    IMG_6747.JPG

    0-18 likewise has the straightedge below the top of the bridge. Action is 0.080 to 0.115 which is playable but pretty high. Saddle is 0.070 out of the bridge so it can’t be lowered much. Guitar is marginally playable but would benefit from having the neck reset

    IMG_6729.JPG

    All of these guitars are playable, two will need work eventually. For comparison, here is a guitar (not a Martin) that is badly in need of a reset – it is pretty much not playable

    IMG_5528.JPG

    Neck resets are not trivial but most guitars will need one at somewhere around 30 or 40 years of age. The process on Martins is invasive and expensive, but it can change the character of the instrument. My feeling is that if I encountered a guitar that I really liked but knew it needed a reset I would negotiate with the owner for maybe splitting the cost. Most of the time they know, they just don’t want to make the investment.
     
  5. Freeman Keller

    Freeman Keller Poster Extraordinaire

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    FRETS

    Once I’m satisfied that the guitar is healthy – hydration and neck angle – I can consider other items. I usually look at frets next – general condition, are they worn, have they been worked on before? Does the fretboard have divots, how bad are they? I really don’t have any metrics here – if they look marginal I will factor the price of a full or partial refret into the decision process. The HD-28 looked fine, I didn’t take any pictures. Here is the 0-18. Slight wear but not bad for a 50 year old guitar.

    IMG_6724.JPG

    The D-18 had been refretted

    IMG_6745.JPG
     
  6. Freeman Keller

    Freeman Keller Poster Extraordinaire

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    STRUCTURAL THINGS, CRACKS, BRIDGE

    Probably the most common “failure” that I see in my shop are bridges coming loose from the top. Its easy to fix, but I check anyway. Often it is a sign that the guitar was too hot – maybe left in the back seat of a car. Just take a thin feeler blade and run around the back edge

    IMG_2006.JPG

    (This is a different guitar, the bridges on all three Martins were nice and tight)

    I also take an inspection mirror and flash light and poke around inside. I always look at the bridge plate – is it all chewed up from the ball ends of the strings? If so it might be a candidate for replacement, which can segue into another discussion about 1970’s Martins and their bridge plates. Replacing is a moderate hassle but can dramatically improve the sound of these guitars.

    While I’ve got the mirror I look at all the braces, particularly the ends, to make sure they are nice and tight. No pictures, sorry.

    Old guitars get cracks, Martin is prone to a couple of special ones. Traditionally they put the pickguard onto unfinished wood and finished over it. The p/g and wood expand at different rates, the wood cracks. Both the 0-18 and the D-18 have pick guard cracks, the one on the dread has been closed and cleated

    IMG_6727.JPG

    IMG_6742.JPG

    A couple of others

    IMG_6728.JPG

    There is sometimes a crack on either side of the fretboard extension right at the sound hole. This is kind of a bad one, the neck is being levered up and driving the f/b extension into the top. There is one big brace and one small one that are supposed to fix this but they don’t always.

    Another Martin crack is the infamous “key crack” on the waist of the guitar right where it sits on the key in your pocket. The D-18 had it

    IMG_6743.JPG

    And here is one last crack that shouldn’t happen. The herringbone was apparently dropped on its butt (maybe even in the case) – the end pin is a tapered and is driven into the hole. It happens the that grain on the end block is oriented the same direction as the sides (so they will expand at the same rate)

    IMG_6721.JPG

    Anytime you ship a guitar take the time to pull the end pin and put it in the case to keep this from happening.

    Cracks need to be stabilized, glued and cleated.
     
  7. Freeman Keller

    Freeman Keller Poster Extraordinaire

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    SADDLE SLOT AND INTONATION

    There were a few Martins in the 1970’s that literally have their saddles in the wrong place. As I understand it the bridges are slotted at an angle but there was no initial compensation added when the bridge was glued on. As you play up the neck the guitar plays a hair sharp. Most people never notice it but a few do. The D-18 has that problem, I don’t notice it

    IMG_6750.JPG

    There are a couple of fixes - the best is to fill the saddle slot and route one in the correct place. If you never go above the 5th fret you'll never notice it.
     
    Last edited: Jun 18, 2021
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  8. Esquire Jones

    Esquire Jones Tele-Meister

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    Nicely done Mr. K.
     
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  9. Freeman Keller

    Freeman Keller Poster Extraordinaire

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    TRUSS RODS AND RELIEF

    Up until about 1980 Martin guitars did not have adjustable truss rods. The do have reinforcement in the necks, ebony in some of the old ones, T or square bars in others. So it is wrong to say they don’t have truss rods, they just don’t adjust.

    The good news is that the old necks are remarkably stable and don’t seem to pull much relief, even with medium gauge strings. Both the 0-18 and D-18 have right at 0.008 of relief which is pretty ideal. There are ways to deal with excessive relief but they are not pretty. The HD has an adjustable rod, relief is not an issue.

    If you are going to look at a used guitar a quick method of measuring the relief is to know that an average business card is about 0.010 and that is the upper limit of what I consider acceptable relief. Put a capo on the guitar, hold a string down over the heel (14th fret usually) and try to slide the business card under the string at 7 or 8. If it is tight that OK, if it is loose you might want to consider, particularly an old Martin with non adjustable truss rods. Two cards is too much relief in my book.

    ps - I'm not going to go thru setup in this discussion, it is a whole topic of its own.
     
    Last edited: Jun 18, 2021
  10. Freeman Keller

    Freeman Keller Poster Extraordinaire

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    FINISH, COSMETICS

    All of these guitars have nitrocellulose lacquer finishes. All have some cracks and flaws and dings – they are well played and well loved instruments. Nitro can be drop filled and over sprayed more easily that modern finishes. I’ve drop filled some of the bad dings but I avoid anything that resembles refinishing. The D-18 has a new pick guard done when the crack was fixed. I think it looks good.

    IMG_6742.JPG

    The 0-18 and HD have their original tuners. They still function and on a guitar approaching vintage status you should at least keep them to sell with the guitar

    IMG_6730.JPG

    I replaced the clunky old Rotomatics on the D-18 with some nice Gotohs – I like the open gear look.

    IMG_6744.JPG
     
  11. Freeman Keller

    Freeman Keller Poster Extraordinaire

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    SUMMARY

    The HD-28 is the newest of the three. It appeared to be dehydrated, but has come back and the neck angle is marginal but acceptable for a little while longer. The butt crack indicates some potential damage (I haven’t investigated yet). Action is good and the guitar is playable, I would budget for a neck reset in ten years or so. If I was in the market I would wait a month or so to see how it responds to rehydrating.

    The D-18 is my personal guitar and has had all the work done that needed to be done. It is properly hydrated (I keep all my guitars in their cases with a humidifier), neck angle is perfect (had a reset), frets are new. Action is good and will be for a long time. All the cracks are fixed, new tuners, yadda yadda. It had the bridge plate replaced and several people who have played it give it that overused term of “cannon”.

    The 0-18 is a sweet little guitar, I just really enjoyed playing it. It needs a reset and refret and have the cracks fixed (and a new case) – it would be a stunning little finger picker. I would consider a guitar like this but would definitely negotiate – the repairs will not be cheap.

    Hope this helps, hope it will stimulate some conversation.
     
  12. vhilts1

    vhilts1 Tele-Holic

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  13. peteycaster

    peteycaster Tele-Afflicted Silver Supporter

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    Nicely done and very informative as usual. Thankyou again for being so generous with your acquired knowledge.
     
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  14. Deeve

    Deeve Poster Extraordinaire Silver Supporter

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    subscribed - because I've got to come back a few more times to digest this splendid post. Thanks @Freeman Keller :cool:
     
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  15. Tommy Biggs

    Tommy Biggs Friend of Leo's

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    Nice thread. Thanks for sharing your knowledge.
     
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  16. 985plowboy

    985plowboy Poster Extraordinaire

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    Thank you for taking the time to share your knowledge.
    I really like having you around.
     
  17. theprofessor

    theprofessor Poster Extraordinaire

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    Thank you! Wonderful information!
     
  18. etype

    etype Tele-Afflicted

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    Great thread. Thanks!

    When measuring the saddle height above the bridge, as it curves to match the fretboard radius, I assume you measure between the 3rd and 4th strings?
     
  19. rand z

    rand z Friend of Leo's

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    Very Nice!

    Thank You!
     
  20. Freeman Keller

    Freeman Keller Poster Extraordinaire

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    I typically measure it close to the 1st and 6th strings. The saddle is curved to more or less follow the fretboard radius but the bass side is almost always higher. If I have close to 1/8 on the treble side and more on the bass I'm very happy.
     
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