Carbonfibre seatpost stuck in aluminium frame

[STRADA]

Yip, bit of coke around the top, leave for a while, worked before for my mate.

[Delilah]

Yip, bit of coke around the top, leave for a while, worked before for my mate.

Aluminium oxide reacts with both acids and bases, so dilute solutions (for safety) of either should remove the deposit given a bit of time. Coke works, because the dissolved CO2 turns it into carbonic acid. However, the solubility of CO2 (or any gas) in water (Coke) is inversely related to temperature - as the Coke heats up to room temperature the CO2 will go out of solution and dissipate. After a bit of time the remaining sugary water will no longer be effective.

 

A more effective household option would be a solution of citric acid in water. Be sure to rinse the frame and seatpost very well afterwards and dry them too.

 

And yes, I work in a lab

 

PS: IIRC Coke also contains a small amount of citric acid, but rather make your own (more concentrated) solution as it will be more effective.

Edited October 4, 2012 by Delilah

[V12man]

@ Johan - the OP said with no damage - saw's count as damage in my book - very much a last resort.

 

2 squirts of the right penetrating oil (anyone that dissolves/penetrates rust will be fine) , leave overnight and 10 seconds with the slide - will be out - I guarantee.

 

As Delilah said - Aluminium oxide is removable, just like iron oxide is too (rust), although my understanding is that coke also has small traces of phosphoric acid too (or used to have in the mid eighties when we used it for some testing) - and that is brilliant at dissolving just about anything - including glass at the right concentrations.

[Johan Bornman]

Fortunately, aluminum oxide can be dissolved like magic by using ammonia. Worked twice for me in the past. Submerge in ammonia for a day or two.

 

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

 

Yes, but unfortunately the area of attack is so small that full penetration just about never happens. What I mean by this is that the oxide forms perfectly good seal in there and pouring ammonia in only attacks the axial end of the little cylinder of oxide. I'm not sure if my explanation makes sense but it is the converse of say, painting ammonia onto a sheet of aluminium oxide.

[duringd]

The bigger the problem, the bigger the hammer!!!!

[DoubleDee]

Thanks for all the advice! Going to try the less aggressive methods first and will let you know the outcome!

[Meentb]

What was the outcome?

[SURFER]

Let us know

[Wallee]

 

2 squirts of the right penetrating oil (anyone that dissolves/penetrates rust will be fine) , leave overnight and 10 seconds with the slide - will be out - I guarantee.

 

 

Incorrect. I have been spraying penetrating oil onto the seat post/seat tube everyday for the last two weeks. Seatpost won't budge. Time for more drastic measures.

[Zatopek]

I had to saw a broken seatpost out.

 

Regular phone photos to see whats going on helped. It was quick throught the first 80% of the seappost wall thickness, but the last 0.2mm take SO long because you are so carefull.

 

A week of Q20 and these steps was attempted & failed: (I had two little points and the frame clamp slot to drill 3 holes for a brake cable)

• Fill the frame with ice cold water.
• I tried hanging with my full body weight on it - nothing
• I tried to rotate/wiggle it by drilling a 3mm horizontal hole trough the ~5mm clamp slot, trough a smaller diameter steel pipe and into 1/2 of the seatpost on the other side - no luck, the drill bit broke first. 
• Pull on it with my grandpa's farm fence puller - no luck, the brake cables broke first. (so the pull force would have been more than my 96kg weight)