Stuck carbon seat post in a steel frame , ideas?

Discussion in 'Bicycle Mechanics and Repairs' started by FishFright, 13 Feb 2018.

  1. FishFright

    FishFright More wheels than sense

    I have a carbon seatpost (no debates please) stuck in a steel frame and I need to remove it but I can't get it to budge yet. Survival of the frame and paint is a must but I'm less bothered about the post .

    Any good , or failing that funny, ideas on how to get them out of this deadly embrace ?
  2. mattobrien

    mattobrien Veteran

    Sunny Suffolk
    My LBS ended up turning the frame upside down and using a bottle of coke to free up a very stuck carbon seat post, albeit in an alu frame. It wasn’t budging at all prior to that.
  3. Hugh Manatee

    Hugh Manatee Veteran

    When I was on holiday, I left my carbon fishing rod set up all week. When I came to go home, all my heft couldn't separate the first two sections. In somewhat of a panic, I made ice cubes, crushed them and packed them around the rod. A couple of minutes later and they slid apart with no damage. Worth a try if you can get it cold enough. I was told that certain spray lubes and get into carbon and cause it to swell. I don't know if this is true as the only carbon I have is also a seatpost!
    At least if it comes to it, it'll be easy (ish) to cut out.
    Cycleops and FishFright like this.
  4. iluvmybike

    iluvmybike Well-Known Member

  5. PeteXXX

    PeteXXX Cake or ice cream? The choice is endless ...

    Pop it all in the microwave for 8 minutes on high..
    The variable coefficients of expansion will soon work to your advantage :okay:
  6. Cycleops

    Cycleops Guru

    Accra, Ghana
    You might just have a tiny bit of trouble finding a microwave that big and even if you could the steel would short out the oven.
  7. Milkfloat

    Milkfloat Veteran

    A microwave is just overkill - everyone knows that carbon melts in the rain, so just lob the frame in your waterbutt for a week.

    If that fails - you could try this from Sheldon.

    "Then I stepped back to my engineering thinking (for last 20 years I design and build special prototype machinery). First I checked on the heating / cooling options and found that the thermal expansion of carbon epoxy composites is only 0.000001/F which makes it one of the materials with absolutely best thermal stability - forget about heating or cooling carbon - it will not help and may only damage the frame.

    Then I started to analyze the physics of pulling one composite tube out of another. I was sure it was not glued together, as the frame is old enough to be perfectly cured and the tube was there only for a few weeks. It was only held there by friction. It was not inserted with a lot of force so it must have created some mechanism that locks the pieces together. My further conclusion was that if you pull on the frame trying to pull out the post you are causing the seat tube to elongate, which in turn reduces its diameter and causes even tighter clamping on the post. The more force you apply pulling on the seat tube, the It is exactly what happens when you put one piece of plastic tubing in another piece of tubing and then try to pull it out [like a Chinese finger puzzle -- John Allen].

    The best way to do it is not pulling on the outer tubing, but pushing the big tubing off the small tubing, just pressing on the edge of the outer tube while pulling on the end of the inner tube. Now I knew I would be able to do it. I only needed some way to apply reasonably large force just on the top edge of the seat tube. I took two aluminum plates that just fitted nicely between the seat rail clamp plate and the top of the seat tube (one plate on one side of the seat post and the other on the opposite), with the seat rail clamp screws extended by a few turns. Then I gently turned the rail clamp screws in and the seat post just came out without any struggle :smile: :smile: :smile: I did not apply any more force then, just slight finger pressure on the Allen key while turning the screws. I am sure that a similar method may be used on metal frames and seat posts or any combination of the material. You just need the right length of spacer blocks or some kind of screw attachment to do the pushing off the seat tube from the seat post."
    FishFright likes this.
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