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  1. #1
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    AC seatpost problems

    I'm building a 2003 AC1, and got a 30.9 seatpost for it. Although it fits fine diameter-wise, it won't go into the seat tube more than about 4", and that does not cover the minimum insertion point for the post (not to mention that it's too tall for me). Apparently there is a constriction at that point in the seat tube that reduces its diameter to an unknown size. I've seen quite a few posts from people having installed such a size seatpost, so I was wondering how you guys did it. Is cutting the seatpost an option, or is the shim the only way to go?

    Appreciate any ideas/experiences.

    John

  2. #2
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    It sounds like you need to run a ball hone through the seat tube to clean it up. A good bike shop will have a hone for this purpose.

  3. #3
    Dr. Porkenheimer
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    Seattube construction

    My understanding (you should check previous posts in this forum on this topic for more details) is that there is a tab inside the seattube that prevents use of seatposts without the shim.

  4. #4
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    Quote Originally Posted by bykhed
    My understanding (you should check previous posts in this forum on this topic for more details) is that there is a tab inside the seattube that prevents use of seatposts without the shim.
    I did check all previous posts on this subject and there were a number of people who had made the transition to a 30.9mm post apparently without any issues, so that's why I was surprised to find out that the seat tube does not really support this size post -- and again, I never saw any mention of such a constriction in any previous messages.

    John

  5. #5
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    You probably have some manufacturing flashing/junk down in the tube. As I stated earlier, running a quick hone through it will clean it up.

  6. #6
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    Quote Originally Posted by Wheelie
    You probably have some manufacturing flashing/junk down in the tube. As I stated earlier, running a quick hone through it will clean it up.
    I wish it was some junk, but unfortunately the seat tube simply narrows down -- the bottom of it is narrower than the top. Yes, one could hone that too, but I am not going to second guess the manufacturer and risk the frame. The height right now is marginal, so I may stay with it, or maybe cut off an inch or two; I only weigh 135 pounds so I won't be putting too much stress to it anyway.

    John

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