Author Topic: Dissolving a stuck Seat post with Caustic Soda (FIXED)  (Read 28425 times)

LEE

Dissolving a stuck Seat post with Caustic Soda (FIXED)
« on: August 16, 2010, 02:58:51 pm »
UPDATE - See end of thread for info on my successful use of Caustic Soda to remove a stuck seatpost

My LBS has failed to get my stuck seat post outof my Thorn Raven seat tube and both Thorn and Mercian have recommended hack-sawing from the inside (after cutting the seat post off with an inch to spare).

That method is failing due to length of seat post inside frame.

I understand that the problem is Aluminium Oxide binding up against the steel frame tube.  

Some people recommend WD40.  Failed (after a week of soaking)
Some people recommend filling seat tube with Coke.  Failed (after 2 days)

Luckily it is easy to plug the B/B (using a wine cork) so I am free to pour anything into it.  

What should I pour into it now?

Ammonia?  I believe that is a solvent for Al Oxide and may break the bond.  Where would I get it from?  A fairly dilute mixture left overnight may work without getting nasty.

Sodium Hydroxide / Caustic Soda ?  I believe that will dissolve the Alloy itself.  I know it's nasty stuff but I can protect most of the paintwork (the underside of the B/B may need some Hammerite afterwards).  Where do I get this stuff? I want to pour "dry mix" into a tube full of water rather than pouring nasty stuff over my bike.

Basically I have 1 inch of mangled seat post sticking out of the frame to grap with a wrench but I first need to soften up the alloy/steel bond because I'm running out of seat post to twist.


Any ideas?


PaulF

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Re: Dissolving an Alloy Seat post
« Reply #1 on: August 16, 2010, 03:03:37 pm »
Have you tried Just Bikes on the High Street? They managed to shift a bottom bracket that others wouldn't even look at.

Re: Dissolving an Alloy Seat post
« Reply #2 on: August 16, 2010, 03:10:14 pm »
Have you tried the Sheldon method of clamping the seatpost (stub) in a vice and using the frame as a  lever?  You could drill a hole through both sides of the seatpost stub and put a bar through (eg old axle), thereby giving the vice something substantial to grip.

Re: Dissolving an Alloy Seat post
« Reply #3 on: August 16, 2010, 03:11:45 pm »
Diesel fuel is quite good penetrating oil I understand.  But perserverance with the hacksaw should also work.
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Martin

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Re: Dissolving an Alloy Seat post
« Reply #4 on: August 16, 2010, 03:16:42 pm »
Have you tried the Sheldon method of clamping the seatpost (stub) in a vice and using the frame as a  lever?  You could drill a hole through both sides of the seatpost stub and put a bar through (eg old axle), thereby giving the vice something substantial to grip.

I tried that to free a stuck BB; result one broken vice  :(

if you hadn't sawn the sitpin off I'd suggest wedging the square top of the seat pin in a drain cover and twsiting the frame, that worked for my son's jump bike; you could try Martin 109's t bar idea in conjunction with this;

NB; if you start deforming the seatpin too close to the frame you may end up also deforming the latter and then you'll never get anything in it again.

(nb when you do get it out ensure you liberally smear the new one in grease that will help prevent the oxide from sticking to the frame.)

Biggsy

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Re: Dissolving an Alloy Seat post
« Reply #5 on: August 16, 2010, 03:24:45 pm »
Sheldon mentions ammonia here.  It's available from chemists and DIY stores.
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LEE

Re: Dissolving an Alloy Seat post
« Reply #6 on: August 16, 2010, 03:27:22 pm »
The LBS tried the upside-down-in-a-vice method but got worried about damaging the frame and said they wouldn't force it any more than they did.

I'll try ammonia.

inc

Re: Dissolving an Alloy Seat post
« Reply #7 on: August 16, 2010, 03:28:54 pm »
Maybe try this Pipe Freezing Kit 220ml - Screwfix.com, Where the Trade Buys to shrink it enough to break the grip

Martin

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Re: Dissolving an Alloy Seat post
« Reply #8 on: August 16, 2010, 03:31:16 pm »
you could drill it out with successive bigger sized auger bits or similar but unless it's done on a jig you will probably bugger the frame.

Is this the one you bought last year after your one died in Lymington?

LEE

Re: Dissolving an Alloy Seat post
« Reply #9 on: August 16, 2010, 04:02:57 pm »
Argos Cycles said they could do it and seemed fairly unconcerned.

I'll send it off there.

Re: Dissolving an Alloy Seat post
« Reply #10 on: August 16, 2010, 04:42:20 pm »
Try the ammonia first. It worked for me.
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Re: Dissolving an Alloy Seat post
« Reply #11 on: August 16, 2010, 05:19:16 pm »
Not a seat post in this instance.

However, another endorsement for Ammonia.

Re: Dissolving an Alloy Seat post
« Reply #12 on: August 16, 2010, 08:49:23 pm »
Argos Cycles said they could do it and seemed fairly unconcerned.

I'll send it off there.

Gary at Argos is very laid back, but extremely good at what he does!

Re: Dissolving an Alloy Seat post
« Reply #13 on: August 18, 2010, 05:32:27 pm »
I once bought a steel frame for  £2.50 because of the stuck seatpost. Tried Molegrips, Penetrating Fluids, Diesel etc,no change .Tried cutting it longways with a Hacksaw blade to peel it out; useless.
Igot it out in the end by this method;
Remove bottom bracket, Plug hole at bottom of seat tube with apiece of wood.
Buy some sink unblocker/ Caustic soda from local BnQ or Hardware shop.
Fill seat tube to within 2" of top with Caustic soda, add small amount of cold water
Leave about a week, topping up as necessary with water and Caustic.
Seatpost should have dissolved,
Wash seat tube out well.
No idea about ammonia, would try that first, might be able to get it from your local chemist.

Re: Dissolving an Alloy Seat post
« Reply #14 on: August 18, 2010, 09:21:23 pm »
Why do I have this mental picture of bike frames melting and flowing into nearest drain........
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Re: Dissolving an Alloy Seat post
« Reply #15 on: August 19, 2010, 07:55:26 am »
I too was amazed. It was a last resort, but it didn't even damage the paintwork! Steel frames only though.

Re: Dissolving an Alloy Seat post
« Reply #16 on: August 19, 2010, 10:30:22 pm »
More on caustic soda seatpost removal here.

andygates

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Re: Dissolving an Alloy Seat post
« Reply #17 on: August 20, 2010, 09:15:32 am »
Mad chemical violence, I approve but I shudder.

I'd take a hacksaw blade and, from inside, cut the tube lengthways twice, into two long c-shape parts that should then emerge with modest violence.
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LEE

Re: Dissolving an Alloy Seat post
« Reply #18 on: August 20, 2010, 09:46:40 am »
Mad chemical violence, I approve but I shudder.

I'd take a hacksaw blade and, from inside, cut the tube lengthways twice, into two long c-shape parts that should then emerge with modest violence.

My seat post was inordinately long, longer than a regular hacksaw blade anyway.  When a hacksaw blade is fitted into any sort of handle that shortens it even further.  It was just too hard to get any pressure on the blade.  I was sawing for hours ver a few days and it didn't have much impact apart from near the top few inches.


YahudaMoon

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Re: Dissolving an Alloy Seat post
« Reply #19 on: August 20, 2010, 09:55:53 am »
Hi. I had the same problem on a old Giant Peloton steel road frame a friend gave me. Tried most the thing's your trying. I gave in as the frame's paint work was poor anyway unlike yours and removed all the components on one of the cookers hobs to get a like jet effect of gas firing up and placed the not going anywhere seat-post and frame over the jet of fire for 5 minutes and hey ! It came out a dream ! I now have a frame that needs a full paint job.

Steve Kish

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Re: Dissolving an Alloy Seat post
« Reply #20 on: August 20, 2010, 10:01:40 am »
FWIW, I got a CO2 / MAPP gas torch onto an old alloy brake stirrup, just to see what would happen.

Didn't have to wait too long for it to suddenly melt into molten alloy. ::-)
Old enough to know better!

Re: Dissolving an Alloy Seat post
« Reply #21 on: August 20, 2010, 11:52:49 am »
Personally I wouldn't go near an old steel frame with a plumber's blowtorch.

You don't know what brazing alloys have been used, and could end up de-brazing joints on the frame.

A hacksaw will work, it will just be tedious and slow.
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LEE

Re: Dissolving an Alloy Seat post
« Reply #22 on: November 13, 2010, 10:01:26 am »
The latest intstallment of my seat post removal:

I was going to send the frame to Mercian, they charge £25 for seat post removal (plus £30 collection and delivery).  £55 seemed acceptible.  I asked them if they would be using Caustic Soda and they laughed "No chance, we've tried that and it doesn't work, we use a torch to melt it out".

So, now I needed to add the cost of a respray.  Suddenly I was looking at £150.

Down to the Hardware shop for some Caustic Soda (£2.90 for 500g)

I first needed to seal the bottom bracket.  Blu-Tack works (I tested it overnight in a tub of Caustic solution and it looked unharmed).  I wedged a big plug of it up the seat tube (Fnnarr Fnnarr) and secured it with cable ties.  

That done I mixed a batch at "drain cleaning Strength" and poured it in.  Lots of fizzing, lots of heat and lots of gas.  As a control I also left an offcut of seat post in the remaining solution (I wanted to see how effective it was).

Next morning there was still quite a lot of fizzing and the control showed signs of erosion but there was no visible signs that the seat post was any thinner.

Emptied into bucket and repeated overnight.  Same outcome.  Lots of flaky alloy but it looked as sturdy as ever.

Emptied into bucket.  This time, instead of 100g/500ml  I just guessed and created my own mix (I reckon about 150g/150ml.  Poured into frame and waited.  After 2 minutes I had to run to grab a watering can to wash away the bubbling froth pouring out of the seat tube, Holy Crapola this stuff really hated Alloy!.

As fast as I was dousing the frame it was drying out with a white residue, god knows how hot the frame was but I wasn't touching it.  After 10 minutes it subsided to a point where I could leave it overnight.

I repeated the process last night and revisited this morning.

My control seat post is now noticibly thin, as thin as a knife blade I'd say (in fact I think some of it has totally dissolved, the sharp edge being it's last grasp onto life).

I emptied the frame and poured some of my "XXXX super mix" in.  After the expected Vesuvius period I poked a bit of seat post (a ragged remnant of where I had tried hacksawing) and it fell off, into the frame (wow, it must be getting very thin in there now).

I reckon the procedure will be over tomorrow.  Either there will be nothing left or I should be able to poke it free with a long screwdriver.

So that's about it.  I masked off my paintwork with Duck Tape but I doubt whether that will have done much as the extreme heat melted the adhesive.  I'll know more when I've had a chance to clean it.

This process has taken a week in total but I reckon it's a 4-5 day process using a strong mix.

Final report tomorrow hopefully when I assess the damage.

Note.  Steel Frame / Alloy Seat Post.  This is not something you would do with an alloy frame (unless you thought the frame tubes were annoyingly thick)



Re: Dissolving an Alloy Seat post
« Reply #23 on: November 13, 2010, 11:45:37 am »
I freed one on my wife's bike. Let it soak in Ammonia for a week and it what was left pulled out with mole grips. Got the ammonia from a local hardware shop.
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Re: Dissolving an Alloy Seat post
« Reply #24 on: November 13, 2010, 12:20:45 pm »
The latest intstallment of my seat post removal:

I was going to send the frame to Mercian, they charge £25 for seat post removal (plus £30 collection and delivery).  £55 seemed acceptible.  I asked them if they would be using Caustic Soda and they laughed "No chance, we've tried that and it doesn't work, we use a torch to melt it out".


Excellent LEE. As you've detected, caustic certainly does work - I've seen quite a few threads on LFGSS describing the process.