Ammonia for stuck seatpost

[messiah]

Did it once: alloy post stuck in steel frame. Dissolved the post allright but left a complete mess of aluminium residue which required a lot of effort to remove. Damaged the paint on the steel frame as well so we still ended up respraying despite setting out to avoid doing that.

Alloy post in alloy frame- DO NOT DO THIS!

How much seatpost is stuck? A few inches or much more? Have you damaged the post yet or can you still get a grip on it - leave it with penetrating oil and keep trying.

Will it move at all? - Any movement may allow you to get some cutting paste in there.

Heat might not be the best way either: have you thought about trying to cut the post out with a hacksaw blade? Cut it about an inch from the frame and then hacksaw down the inside and cut into it in lots of places to weaken it and try to peel it out. Lots of effort but probably the best solution.

 

[porkypaw]

I've found the best way to get penetrating oil down the post, is to turn the frame upside down, clamp the the top of the seat post in a vice, remove the bottom bracket and squirt shed loads of oil down the seat tube then leave for a couple of days. Use the frame as a lever with the top of the post still clamped upside down in the vice. USE CAUTION :!: Watch for frame deforming/paint cracking if seat post won't budge, a good hit downwards on top of the post might just get it moving --Good Luck :roll:

 

[cornholio's RC200]

Watch out if you use coke/ammonia - strip everything down first. Don't do as I did and end up with a completely useless XT headset when some of the coke went through the downtube as well as the seat tube

 

[twiddler]

Ammonia is a strong alkali.

Aluminium is attacked by strong alkalis such as ammonia, sodium hydroxide (aka caustic soda, lye)

So using ammonia on an ally post in an ally frame is not a good idea.

Iron is attacked by strong acids but not alkalis so ammonia won't touch a rusted steel BB in a steel frame. If anything the water in the ammoina will just help to further corrosion.

Whatever chemical you use please be extremely careful and wear an overall, rubber gloves and as a minimum safety glasses or much better goggles.

It only takes a tiny splash of acid or alkali in your eye to cause serious trouble. Brushing items to clean them eg with tooth brushes produces droplets which can carry a long way.

There are MSDS ( Material Safety Data Sheets) on the internet which give basic advice on handling specific chemicals.

 

[Corduroyboy]

Watch out if you use coke/ammonia

No!

 

[Corduroyboy]

Ammonia is a strong alkali.

Aluminium is attacked by strong alkalis such as ammonia, sodium hydroxide (aka caustic soda, lye)

So using ammonia on an ally post in an ally frame is not a good idea.

Yes!

 

[GrumbleJay]

Mmmmm - first time I've heard y'all saying NOT to follow Sheldon's advice!

It is aluminium in aluminium, frame is stripped, and believe me vices, leverage and shock have all been tried. Penetrating oil would not touch it.

So it seems that I have 3 options:
1) Sheldon's hacksaw method - very tedious and sounds prone to error.
2) Pay to get it reamed out if I can find someone to do it.
3) Sheldon's ammonia method - but that's starting to sound a bit dodgy.

Guess I need to go buy a bundle of junior hacksaw blades. Sigh

Thanks for all the comments

 

[Corduroyboy]

There is 'Option 4'

Cut the 'post so that it is flush with the top of the seat tube. Cut out a slot that closely follows the one in the seat tube which allows the 'post to be clamped. Get a smaller diameter seatpost that matches the internal diameter of the original stuck 'post. Hey presto, the old, stuck seatpost is a permanent shim. Trust me, it can work!

Potential problems:
a) You don't have enough stuck seatpost in the frame to support a narrower diameter one.
b) You have an internally butted 'post stuck in your frame which means it will taper outwards as you go further down, so won't adequately clamp the smaller diameter 'post
c) The internal diameter of the stuck 'post is pathetically small!

 

[twiddler]

Not tried these myself but what about

1. vibration - idea is to break the bond between the two items.

e.g. like you get out of an SDS hammer drill on hammer stop ? i.e. the setting used for chiselling. I would put a wide chisel bit in the chuck, set to hammer stop. put the frame on blankets to protect it when it starts to vibrate THEN

Either place the chisel bit on the end of the seat post & fire away - risk that post could be pushed further into the seat tube - but if it moves it's freed up.

Or pick a point on the seat post & attack it from the side but far away enough from the frame such that it won't get mangled when the chisel slips. you could notch the post with a file which might help

2. drill a 6mm - 10mm or so hole right through the centre of the post and insert a suitably long bar. You could drill another at 90 deg. to the first make sure that they are at least 50mm apart and use two bars. Try to clamp or wedge the frame somehow so that when you lean on the bars that wherever the frame want's to twist it can't. This idea will give you extra leverage whatever other methods you try but be careful as the post might fail under the load.


3. I really, really don't like this idea but ...

Cut off the top of the post.

Find a way to plug the bottom of it in the frame to stop any liquid poured down the centre of the post from leaking into the seat tube. I'm thinking plasticine.

Pour alkali into the top of the post & wait for it to reduce the metal down to a thickness where it will collapse.

When finished thoroughly flush away the alkaline water otherwise corrosion will ensue.

4. Hot & cold

Wrap the seat tube in towels & tape in place like pipe lagging

Saw off top of post as in 3. & try to plug end as before not so critical this time. Cover the outside of the post wher you dont need to grip it in pipe lagging- pack the space with salt and ice - this is colder than ice alone.

Pour boiling water on the towels. Idea is to shrink the post & expand the seat tube.

When finished thoroughly flush away the salty water otherwise corrosion will ensue.

Reaming out is a great idea but my concern is a 27mm or so expanding reamer of the length that might be needed is a very expensive item.

Good luck

 

[Xesh]

One other solution you might try is to cut off the post level with the frame and then push the rest down into the seat tube. It's usually a lot easier to knock the post down than it is to remove it. Not very good, I know, but most seatposts rarely reach more than halfway down the seat tube (unless it's a really small frame).

Personally, if it was my frame, I'd get it reamed out by a frame builder if it's a good quality frame. If it's just a run about then use the above method.

Everyone keeps going on about ammonia. Don't you mean caustic soda? If so that's a completely different chemical. My local frame builder always uses caustic soda for stuck seatposts in steel frames. If it's in an alloy frame then he always reams it out.