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stuck seat post

pastryboypastryboy Posts: 1,385
edited September 2012 in The workshop
Post is aluminium, frame is steel.

So far I've put a load of plus gas in it overnight (sprayed around the post and sprayed into the bottle cage mount to get it from the other end) and used a flat screwdriver to prise away at it - there's a fraction of a mm of play in it now so I put loads of more plus gas in it.

I'm not Geoff Capes but I've got a reasonable amount of strength and the thing just won't budge at all. I'm standing on the frame and pulling upwards on the saddle.

I could try whacking it down with a 6lb hammer to try and free it a bit but I'm wary of it getting stuck further down or doing serious damage.

Does anyone have any other ideas.

I can't twist it because the saddle clamp rotates when I try.

Posts

  • AnonymousAnonymous Posts: 79,667
    Essentially they've created a bond between the two materials, between alloy and steel the bond is usually alkaline, so perhaps try some sort of light acid down the seat tube, (coke, lemon juice, pee in it)

    Or try taking it out for a ride with the clamp loose, the vibrations from the road with your weight on it should help move it
  • pastryboypastryboy Posts: 1,385
    Thanks - I'll try some lemon juice in it next.
  • supersonicsupersonic Posts: 82,708 Lives Here
    Post on a vice, frame as a lever.
    GT ZASKAR CARBON TEAM

    VOODOO CANZO

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  • nicklousenicklouse Posts: 50,675 Lives Here
    Read the topic on this on sheldons pages.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • pastryboypastryboy Posts: 1,385
    Don't own a vice, did read Sheldon's page.

    Now had several gallons of gas plus and some waitrose lemon juice in there, several whacks with a heavy hammer (up and down) and still not budging at all.

    I've got a cook's blowtorch but I imagine that would be goodbye paintwork.
  • gosport_commutergosport_commuter Posts: 185
    edited September 2012
    If the seat post is sacraficial (which by now im sure it is), you could attempt drilling a cross hole near the top of the post (so if it goes wrong you still have something else to work with) and using a bar through it as a lever to twist.

    EDIT: make sure the cross hole is a good fit for whaetever you intend to use as a lever.

    EDIT2: Don't use heat - the aluminium will expand at a greater rate than the steel, making the fit EVEN tighter. Walk in freezer might help lol!
  • gosport_commutergosport_commuter Posts: 185
    Failing that - take it to a small engineering firm.
  • pastryboypastryboy Posts: 1,385
    A night soaked in the lemon juice didn't help. Not sure if I want to pour a pint of vinegar down there next.

    I might try freezing the seat post to make it contract. Heston Blumenthal did thing on his show where he used cans of compressed air (sprayed upside down) in place of liquid nitrogen. I tried it myself to speed up a sorbet and it worked a treat.

    I really don't know how it got so stuck. It slipped a bit ages ago so I lifted and tightened it with a plain old little multi-tool. Only wanted to make a really minor adjustment this time so I might have to just live with it as it is till I get some more compressed air.
  • The RookieThe Rookie Posts: 27,809
    As the aluminium oxidises in the electrolytic action with the steel, the resultant oxide has a much larger volume and fills the gap (and a bit more) wedging in in place.

    The post is now scrap, twisting is best to loosen the oxide, use a cheap old heavyweight solid steel railed saddle and twist it., once it starts to loosen move it up and down as well, keep going and eventually it will come free.
    Current steed - Whyte T129, 2013 frame, mongrel Revelations, Giant dropper, Stans S1 wheelset. 12, Magura Trail Sport brakes, 1x11. 12.8Kg
  • bails87bails87 Posts: 12,998
    If you use a can of compressed air remember to wear gloves or it'll stick to your hand!
    MTB/CX

    "As I said last time, it won't happen again."
  • Harry182Harry182 Posts: 1,168
    I had this exact same problem. I ended up cutting the top of the post off with a hacksaw leaving about an inch of post above the frame. I then used a junior hacksaw blade down the centre of the post stump to cut a slot out of the length of the remaining post (does that make sense?). The aluminium cuts pretty easily and the steel frame doesn't. So, with a bit of care it's easy to cut the post and barely touch the frame. And finally, I used a pair of vice-grips (I think they're called mole-grips in the UK) to grab and squeeze the protruding bit of the post stump. The vice-grips squeezed the post stump enough to slightly pull it away from the frame allowing it to fairly easily be twisted out. Before installing your new post you'll probably need to have the seat tube reamed - your lbs should be able to for a few quid.
  • Daz555Daz555 Posts: 3,976
    Don't hammer it into the tube.

    Go and see a friendly LBS or car mechanic or any local workshop and ask em to use their vice - chuck em a tenner if it helps. Grip post in vice (crush it if you have to) and use frame as a lever. It will move.
    You only need two tools: WD40 and Duck Tape.
    If it doesn't move and should, use the WD40.
    If it shouldn't move and does, use the tape.
  • BOYDIEBOYDIE Posts: 528
    I had this same problem 6 months ago, take it to some one with a vice, crush the seatpost until flat and use the frame as a lever and twist it of the seat post. You will need a new seatpost but I would rather pay £10-£20 rather than damage a frame.
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