What to pour down it

[simon the viking]

On my spare bike (The Viking) I have a stuck seat post and have had for a while (I had another thread running about how to remove and nothing suggested worked.... although I haven't tried to cut it out with a hacksaw)

I can now take it off the road for a few days, remove the bottom bracket out and tip something down it to try and free it.... what would you use?

EDIT: Sorry should have said its a steel frame/alloy post

 

[Canrider]

Soak it in WD-40?

(runs for cover)

 

[oldstrath]

is it steel frame? If so Coke or NaOH

 

[simon the viking]

is it steel frame? If so Coke or NaOH

See edit

 

[simon the viking]

Soak it in WD-40?

(runs for cover)

tried that from the top.... but thought Plusgas would be better if I'm going to the effort of removing bottom bracket

 

[Amanda P]

I had this, and if you look you can find the thread, complete with photos, describing the saga. Yes, it came out in the end.

Yep, turn the frame upside down and clamp the seat post firmly in an immovable vice. Mix up caustic soda carefully (it foams and gets hot) and squirt it into the down tube - a big syringe and bit of tube is handy for this - a hydraulic brake bleeding kit is ideal. Leave it overnight.

Then try twisting the frame. If you can't twist it and lift it off the seatpost, drain out the soda, make another batch and do it all over again.

Repeat as necessary. It might take several goes.

 

[Amanda P]

Oh, you're probably not going to be able to rescue the seat post.

What happens here is that the alloy seat post corrodes. The oxide that forms in the tiny space between the post and frame is bulkier than the original alloy, so effectively the seatpost swells. NaOH dissolves the oxide, and the alloy eventually. But most of the solution you pour down ends up in contact with the inside of the alloy post, where it does no good. It reacts with the aluminium there and is neutralised - that's why you need to pour it out and replace it periodically - when it's not longer foaming, it's no longer reacting.

And of course, only the thin ring of corrosion at the base of the seat post is in contact with the solution at any given time, so it takes a while for the corrosion to be dissolved.

 

[oldstrath]

tried that from the top.... but thought Plusgas would be better if I'm going to the effort of removing bottom bracket

Plusgas almost certainly won't do anything much - as Uncle Phil says, sodium hydroxide is the way to go (carefully)

 

[simon the viking]

Thanks folks, I figured the seat post would be scrap afterwards, caustic soda seems to be the most popular choice.... I will source some at the weekend and keep you (dare I say it...... ) Posted......

 

[HLaB]

Its similar I believe but after just 2 and a bit months my alu seat post has seized solid in a Ti frame; I liberally soaked it with Wilco's version of WD40 last night hopefully it'll budge tonight, if not I'll soak it a bit longer and if that doesn't work I'll investigate CO2 and if it still wont budge I'll investigate more destructive measures (such as a hack saw). I may however, if the WD40 doesn't work take it to a bike shop

http://sheldonbrown.com/stuck-seatposts.html

 

[simon the viking]

Me and lbs staff had my seat post in a vice after it had been soaked in WD40 and "freeze it" spray.....the frame was going to bend before the seat post moved! I rode the bike with the clamp undone and aimed for every speed bump.... nothing so tightened it up and left.. now with a new bike I can have another go and keep it off the road while I try

 

[ayceejay]

Thomson, who make excellent seat posts, suggest that you remove and clean a post every 90 days. While this will not help you now it may be something for the future.
this you tube entry may help
View: http://www.youtube.com/watch?v=54WhdrLKKvY

 

[mr messy]

Tempted to say chop post then crush to allow chemical of your choice access from top.
Nature of this type of bi-metallic corrosion tends to end with alloy destruction. Only quick way to release is the fiery spanner....

 

[HLaB]

Wilco's WD40 worked for me and rotating the post out with an old saddle, so I'd try something less destructive first :-)

 

[derrick]

Hair drier, get it nice and warm. the frame not the seat post. lots of wd40.