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  1. #1
    Senior Member
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    NaOH removes seatpost

    The bike is a 1984 Bridgestone MB-2. Help with Apparent Bridgestone MB-2 in Japan (See the pic by lefthread; that's what I got)

    Here's another thread. This one about the idea of drilling out the 8.6 inches of seatpost stuck in the CroMo seat tube.


    Drilling out Al seatpost: Any succeses?

    Anyway, I redid the hacksaw technique with some high-quality high-speed steel blades (32 teeth per inch). Over the course of a few hours I made five cuts lengthwise (great blades!). Judging from the sound, I knew had reached the steel seat tube. Also the blade was flush along the tube. With victory in sight, I pried a section from the tube using very stout, extra-long needle-nose pliers. Got about three inches off the tube and no more; same with the remaining four sections. How much force was I using? The pliers are bent; the jaws are no longer in alignment. For various reasons, I decided against drilling or reaming.

    My last resort was NaOH (sodium hydroxide, also known as caustic soda and lye). Over the course of two and a half days, I refreshed the solution after the reaction had stopped, except at night. I used two table spoons of flakes per 100 cc of water for each refresh except for the finale, for which I doubled that. Man, what a chemistry show that was! After I rinsed out the tube, my wire feeler told me there was almost nothing left. I took the bike over to a work table and tapped the seat tube on a block of wood a few times and out popped the remnants of the seatpost, which I will keep as a reminder of what a PITA this whole thing was.

    The paint held up surprisingly well, with just some streaking here and there. But I was going to have the frame painted anyway.

    Success!!

    If anyone wants to know more details about how I did this, what precautions I took, and so on. Just ask.

    WARNING: Caustic soda is very dangerous! Take no chances. Use extreme care.

    Also see this http://www.classiclightweights.co.uk/seatpin-rest.html

  2. #2
    Great State of Varmint Panthers007's Avatar
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    NaOH (sodium hydroxide, lye, others) will cause severe burns to skin and eyes. Safety-glasses are mandatory as well as rubber/neoprene gloves. Never add water to NaOH - it WILL boil-up and spatter. To dilute - add NaOH to water SLOWLY with stirring. YOU: Have a shower nearby. If it gets on your skin, your skin will feel slippery like soap. Why? Because it turns people/animals INTO SOAP! No kidding. But moving right along:

    NaOH reacts with and dissolves aluminum and aluminum alloys. So this above method will probably work - if the seatpost is also alloy. If it's steel or carbon - forget it. And be very sure of the frame. If the bike's frame is aluminum - it will also be eaten and rendered weakened and unfit to ride. Check all surrounding components also - if any are alloy and get splashed with the NaOH, they will suffer damage.

    To neutralize NaOH - use regular vinegar - repeating and washing with clean water as well. Is all this worth it to you? Be sure you've exhausted all other options before using NaOH. It's a chemical blowtorch.
    How do you keep an idiot in suspense?

  3. #3
    Senior Member
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    What Panthers007 said.

    When I was mixing the flakes and water and getting the NaOH solution into the seat tube, I was wearing rubber boots, elbow-length rubber gloves and another pair of heavier rubber gloves over them, and a head-to-toe vinyl rain suit. I tested the solution on the rain suit before hand. I also wore safety goggles and a mask covering the nose and mouth. I also had a garden hose and a half gallon of vinegar right beside me. I did this outside at the edge of a woods that borders my back yard, about 30 yards from any houses. I was continuously rinsing: rinsing tools, stirrers, my gloves, etc. Have to always keep in mind that you can't wipe off a bead of sweat with your gloved hands.

    Yes, you might say that was overkill, but I did it without injuring myself or anyone else, so I'm satisfied.

    When I was growing up back in Kentucky, a few neighbor ladies made soap with lye regularly, Once, when I was 6 or so I was over at Mrs. M's house when she was cooking soap. I wasn't allowed in the kitchen but I could see the lye beads in a big plastic jar on the counter. I asked her if I could eat a piece of the white candy. She said something like "My, my no. That'll kill you

    I'm having second thoughts about even posting about this experiment now.
    One more edit: I removed ALL parts and components before I did this. The frame was bare.
    Last edited by caintuck; 11-03-09 at 02:23 AM.

  4. #4
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    The usual recommendation for dissolving out a truly stuck aluminum seatpost in a steel or Ti frame is ammonia. NaOH basically acts like ammonia on steroids as it is a much stronger base. It's also, as has been noted, a lot more dangerous to handle.

    Incidentally, one of the by products of the reaction between NaOH and Al is hydrogen gas which made up the bubbles you were seeing. You want to conduct this reaction in an area with plenty of ventillation and, for sure, no smoking!

  5. #5
    Great State of Varmint Panthers007's Avatar
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    Yep ^^^. Playing 'Hindenburg' at home is generally ill-advised. On the + side - if it did catch fire, all that would result is plain water - H2O.
    How do you keep an idiot in suspense?

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