Stuck seat post & ammonia. Anyone tried it?

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timdownieuk
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Stuck seat post & ammonia. Anyone tried it?

Post by timdownieuk »

Well, the strip down was going just fine until I went to whip out the seat post. Alloy seat post stuck solid in steel frame.

I had a look in the "Too good to lose" section and having already failed with Plusgas and pretty physical persuasion, thought I'd try Sheldon Brown's ammonia trick.

Not that I think for one moment that Sheldon Brown could be wrong, but has anyone here actually tried ammonia for freeing a stuck alloy seat post?

Just wondering how long I should leave is steeping for.

Tim
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recordacefromnew
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Re: Stuck seat post & ammonia. Anyone tried it?

Post by recordacefromnew »

I think I have tried pretty much everything, including setting up two car jacks to pull one out (which bent the jacks while the post stayed still...). I think no one can tell you what works for you because it depends on how stuck it is.

What you might be glad to know, is that with a steel frame and alloy post caustic soda always works. IME using a lowish concentration which requires patience there should be hardly any damage to the paint. You can get the crystal from Robert Dyas 2 x 500g for around a fiver. It is nasty stuff, so do take all the safety precautions and plan very carefully where and how you do it, if all else fails.
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timdownieuk
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Re: Stuck seat post & ammonia. Anyone tried it?

Post by timdownieuk »

recordacefromnew wrote:I think I have tried pretty much everything, including setting up two car jacks to pull one out (which bent the jacks while the post stayed still...). I think no one can tell you what works for you because it depends on how stuck it is.

What you might be glad to know, is that with a steel frame and alloy post caustic soda always works. IME using a lowish concentration which requires patience there should be hardly any damage to the paint. You can get the crystal from Robert Dyas 2 x 500g for around a fiver. It is nasty stuff, so do take all the safety precautions and plan very carefully where and how you do it, if all else fails.


The frame is getting stripped for a re-enamel so I'm not worried about the paint. I've only got until Monday morning to extract the post though so if the ammonia doesn't work it may be the caustic soda!
axel_knutt
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Re: Stuck seat post & ammonia. Anyone tried it?

Post by axel_knutt »

“I'm not upset that you lied to me, I'm upset that from now on I can't believe you.”
― Friedrich Nietzsche
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timdownieuk
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Re: Stuck seat post & ammonia. Anyone tried it?

Post by timdownieuk »

axel_knutt wrote:http://www.youtube.com/watch?v=C2XEBLBQPsY


If things haven't loosened tomorrow I'm seriously considering driving it IN a short way with a big hammer on the basis that it'll break any aluminium oxide/steel bond.

Is this madness or worth trying? I've got about 3" of post to play with.

Tim
landsurfer
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Re: Stuck seat post & ammonia. Anyone tried it?

Post by landsurfer »

Borrow a set of STILLSONS, 18 inch should do. Set the jaws until they dig into the seat post as you turn it. Apply torque gently and increase gradually. i have removed 8 alloy seat pins this way in the last 12 months. I used to cut odd the seat post and cut it in a linear way with a skin knife. But the stillsons way works every time , damm site quicker than cutting.
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timdownieuk
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Re: Stuck seat post & ammonia. Anyone tried it?

Post by timdownieuk »

landsurfer wrote:Borrow a set of STILLSONS, 18 inch should do. Set the jaws until they dig into the seat post as you turn it. Apply torque gently and increase gradually. i have removed 8 alloy seat pins this way in the last 12 months. I used to cut odd the seat post and cut it in a linear way with a skin knife. But the stillsons way works every time , damm site quicker than cutting.


I've already clamped seat post in a bench vice and tried twisting the frame. Can't imagine that 18" Stilsons trump the leverage you can get on a full inverted frame (with post in a vice).

Tim
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martin biggs
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Re: Stuck seat post & ammonia. Anyone tried it?

Post by martin biggs »

oh dear stuck seat posts are not good news , must admit had one a while back that i couldnt move by hand and neither could previous owner , a good couple of soaks with plusgas and a few attempts with stilsons did nothing then 2 more attempts out it came , yippee
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andrew_s
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Re: Stuck seat post & ammonia. Anyone tried it?

Post by andrew_s »

Ammonia won't work. It's not strong enough, like vinegar isn't strong enough to do things that nitric, sulphuric or hydrochloric acids will.

Option 1 is brute force - big stillsons, or seat post in a solid bench vice and twist the frame. Be aware that really excessive force can bend the frame.

Option 2 is heat and then brute force. There's quite a lot of water in with the aluminium oxide that's jamming the seatpost in, and heat can drive a lot of it out, reducing the bulk. A hot air gun should do. You are aiming to get it up over 100 deg, but not too far over. Adding penetrating oil like plusgas as it cools will help. If it still doesn't move, it's worth a few more cycles of heat, add oil, cool, and try again.

Option 3 is to cut it out, using a hacksaw blade to make two radial cuts from the inside outwards about 45 degrees apart. When you are almost through to the bike frame, a combination of twisting the small section inwards with mole grips and ramming a screwdriver in the gap should allow you to tear through the remaining metal and curl the seatpost inwards away from the frame. It's slow, hard work, and it needs a lot of care to get the cuts down to the bottom of the post without going through to the frame at the top.

Option 4 is the nuclear option - dissolve out the seatpost with sodium hydroxide (sold as drain cleaner). It's nasty stuff if it gets on you, so wear the full gear - safety goggles, long rubber gloves, rubber/plastic apron, wellies, and work somewhere where any spillage can be hosed off with lots of water. It also generates quite a lot of heat and can spit, both whilst you are mixing the NaOH crystals with water and when it's dissolving the aluminium of the seatpost.
It should go without saying that this only works on a steel frame.
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recordacefromnew
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Re: Stuck seat post & ammonia. Anyone tried it?

Post by recordacefromnew »

If you have a deadline caustic soda is the only sure way. If you don't mind the paint getting some slight discolouring caustic soda solution at 40% strength (100g into 250 ml of water, never pour water onto the crystal - it can be like pouring water on hot oil) will be quite quick. You replace the solution repeatedly when it is spent and the reaction has stopped - to me the whole thing cooling down is a reasonable indication.

To add to andrew_s' safety precautions make sure you do it in a ventilated area. I do it over a spare bath, spills and spits well shielded by shower curtains, with shower hose ready, and the extractor fan on constantly. The reaction generates heat, and hydrogen which is explosive in volume. Make sure the bath has some water if it has an alloy sink hole... :shock: Since diluted caustic soda is commonly used for clearing drains I think there is not much to worry about in terms of environmental concerns.

As I mentioned earlier an important thing is to plan ahead, not just in terms of the obvious deployment of protective safety gears, but also e.g. when the post is partially dissolved and full of holes the solution will leak inside the rest of the frame so you have to be prepared for it bubbling and leaking from the frame's orifices everywhere even a long way away, and needless to say you should remove all alloy parts to avoid them getting partially dissolved.

I believe either way one should cut the seatpost with a couple of inches remaining if not already. The key decision is whether one should block the seat tube at the bb and pour down the cut post, or block the cut post with e.g. a piece of inner tube bound by strings and rubber bands and funnel down from the bb into the seat tube of the inverted frame. It is often not easy to seal the bb without letting the nasty stuff sloshing inside the frame not doing anything while trying to have the post immersed and dissolved, so I think pouring from the bb is usually the better way. You want to cut the post even so because you do not want the top of the post dissolved first while it is still stuck inside the frame - with the post cut you can smear paint or glue or silicone sealant etc. inside the part of the post from just inside to all the way above the frame so that it continues to serve effectively as a plug and is not going to be the first bit that gets dissolved.

One other thing - I try to calculate roughly how much solution is needed to ensure the post is fully immersed. Certainly 250ml is more than enough to start with (when it has no holes for leaking into the frame).

Hope it helps.
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timdownieuk
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Re: Stuck seat post & ammonia. Anyone tried it?

Post by timdownieuk »

Got it!

Brute force and a bench vice eventually worked. Sorry Sheldon, but I'm not convinced that the ammonia did anything. :(

The breakthrough came when I realised that I could reverse the jaw blocks in my vice to expose a smooth flat surface which meant I could clamp up my seat post tighter without having to use anything to protect it. It was still really tough to get beyond a bit of waggling from side to side to full extraction but the seat post is undamaged and fit for re-use.
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