Chemical seatpost removal

[27motorhead]

Awesome thread & description. Lots of mention of caustic soda removal of stuck posts in amongst other threads on this site and numerous others.

Thanks for taking the time to write and record (photographs) the process that will no doubt benefit others.

Ta very mucho!

 

[JimK404]

Ex-teacher of chemistry here, and I feel like I need to add to the safety warnings:

The stated quantities give you 12.5M solution, which is insanely strong. This stuff will dissolve bits of you at least as well as the aluminium, so please make sure:
You have zero exposed skin, including your face - wear a full-face splash-guard.
You can rapidly remove any clothing that gets splashed.
You have a source of large quantities of water - hosepipe is ideal - to dilute any spills.

To give you an idea of how bad this stuff is: as a demo to students I used to dissolve bits of bacon in a solution like this.

 

[Tootyred]

Yes. Safety first.

I did this right next to the outside tap and had a hose spray plugged in and on ready to go, just in case.

But it was quite fun to watch!

 

[wiggviv]

Vinegar is a safe but slow option I have tried caustic in the past with mixed results used plastercine to seal seat tube to bottom bracket. Top results using reverse cut reciprocating saw blade in hand held saw I have some deep section
ones that are near inside diameter of post - steady cutting required clean out swarf as you go.

 

[Blackers]

It took 10 loads to completely dissolve the post. Nothing left.

The last bit ( protected by cork) i pulled out you can see how thin it got.

Nicely done

 

[fearfactoryüberalles]

Nice, but too much hassle-an alloy post in a steel frame only needs a good freezing around the stuck area (sponge attached, soaked in freezing spray)-->alloy shrinks greater/faster than steel-->chemical bond (galvanic corrosion) is broken-->twist & tilt and voilá, boom it goes out, worked me everytime.

 

[Tootyred]

Sadly not this time, as i said above, 3 goes with a pipe freeze kit, no go.. this was the last resort.

 

[fearfactoryüberalles]

Sadly not this time, as i said above, 3 goes with a pipe freeze kit, no go.. this was the last resort.

Must be frustrating, but if I ever need to face this and choose this method as a last resort-my last attempt still would be drilling it out by a machinist ( I know a real good one) or the frame goes straight to the bin/up for karma-not worth the risk/hassle really.

 

[Nabeaquam]

So as some of you will know, i took a chance on an 88 Bear Valley with a stuck post. Mainly as it was reasonably cheap and more importantly my humungous 20.5" c to c size .

The previous owner was very honest and pointed out several times it was stuck......but then there's stuck and STUCK!

This one proved to be the latter......so.....

5 days of supercrack and penetrating oil....fail.
Concussive shock (not too much just air impact with an old socket on top).....fail.
Pipe freeze spray with lagging x3 goes till old tube ran out.....fail.

So its time for some alchemy. Which got it out. Thought i might share the method with you and what i learnt.

Firstly the post was already toast as the previous owner had had several goes in a vice, grips, hammer etc. Pitty as it was an xc pro post! But hey ho. If you want to keep the post try something else as you will have NOTHING left at the end.

Secondly, this method ONLY works on ALLUMINIUM posts in STEEL frames.....i cant stress that enough. The chemicals can't dissolve steel, but can dissolve alluminium......THEY CANT TELL A FRAME FROM A POST, DONT USE THIS ON AN ALLUMINIUM FRAME!

Thirdly, safety first! This is dangerous stuff, it burns.....badly......and will blind you. It also gives of hydrogen as a byproduct. So out doors, no naked flames etc.

If you have any doubts....don't do it.

Still going to try.....excellent.....So you will need for this.

1kg of sodium hydroxide crystals (caustic soda....but check the percentage you need it pure)
Water
Pair of marigolds
Mixing jug......no....not the one from the kitchen!
Safety glasses or better goggles
Mask....able to cope with gas.....depending on location of experiment.
Mixing stick
Tape, bluetack, plumbers mate, potato, prosecco cork for bunging up holes.

I tried this about 10 years ago, left it in for a many days. it still didn’t budge. Theres stuck, stuck and stuck. It was so stuck that I think the sodium hydroxide couldn’t penetrate. I also wondered at the time if the post was hammered in place and then further seized by corrosion. Someone gave me the frame after they had destroyed the post. I used a reciprocating saw and it took hours of careful sawing with the electric saw and a hand held hack saw blade. I worked slowely and would take brakes. It’s hard to do. Similarly, I have removed cotters that were so stuck that my VAR shop grade cotter press could not budge them. If you drill them out with a hole smaller then the pin, then they easily press out. I never want to do either of these again. I’m glad it worked for you. I’ve never tried sodium hydroxide again, as I had doubts about it working after my fiasco with it.

 

[Tootyred]

It was so stuck that I think the sodium hydroxide couldn’t penetrate

If the mix is right, it won't matter how stuck it is....there's nothing left at the end to take out. It literally desolves to nothing! Its not loosening the post it eats it away from the inside of the post out.

You might have needed a stronger mix. I tried 300ml water to 100g of powder and that just made a light fizz, when it stopped and i tipped it out, nothing much seemed to have desolved.

As i said...its not a first (or even second or third) port of call, but when all else failed, it saved the frame in a very (frame) friendly manner.

Im reasonably good with tools, but the idea of trying to run a reciprocating saw or even a hacksaw blade parallel enough, for a 3 whole cuts down 6" of seatpost is not something i wold greatly enjoy......

Glad you got it out though!