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Old 11-12-04, 08:36 AM   #1
max-a-mill
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so i got a piece of aluminum seatpost thoroughly stuck in an older steel frame i just got to try and fix up for my ladyfriend. my big wrench wont budge it.... and it needs to come out!

i heard from someone that it might be possible to melt the aluminum post out by using some sort of chemical??? anyone heard of this madness? or anyother good tips for dislodging a stuck piece of a seatpost?
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Old 11-12-04, 08:58 AM   #2
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Originally Posted by max-a-mill
so i got a piece of aluminum seatpost thoroughly stuck in an older steel frame i just got to try and fix up for my ladyfriend. my big wrench wont budge it.... and it needs to come out!

i heard from someone that it might be possible to melt the aluminum post out by using some sort of chemical??? anyone heard of this madness? or anyother good tips for dislodging a stuck piece of a seatpost?
Safety first! I am not a bike mechanic, but I am a metallurgist. The only thing that will melt aluminum is heat. Most aluminum alloys melt at 660 C (1220 F), however aluminum will also readily burn. I would be careful with any chemicals like acids, as aluminum is a fairly reactive metal. It will generate quite a bit of heat and harmful vapors.

If aluminum oxide (corrosion) is the cause of the "stuckness" you can use ammonia to dissolve it. Or you can always cut it out.

See this website for good ideas:

http://www.sheldonbrown.com/stuck-seatposts.html
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Old 11-12-04, 09:34 AM   #3
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Iíve never heard of melting aluminum with chemicals; you can melt it with heat as a last resort.

When you say you have a piece of seat post in the frame does this mean someone has cut it off and if so is there enough of it that you can hold in a vise? Sometimes you can heat the seat post by pouring boiling water over it. (Outside; not in your living room please.) Aluminum expands at a greater rate than steel so initially this will make it even tighter; however when it cools it contracts and this is sometimes enough to loosen it. Grip the seat post in a vise and twist the frame back and forth.

To melt out the aluminum you are going to destroy the paint and you really need someone who knows how to handle an oxy-acetylene torch. You need what is known as a rosebud tip that gives a very large flame that will heat a large area. The frame needs to be in a vise; upside down. Heat the whole seat tube and seat lug area with the torch moving constantly until the whole area is an even dark red hot. The aluminum will start to melt and drip out; tap the frame with a small hammer further along the seat tube where it is still cold to help shake out the melting aluminum. Do not allow the frame to get to an orange red heat or the brazing will melt. Also when you start heat the frame; do it slowly by holding the torch at some distance and then bring it closer as the frame heats up.
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Old 11-12-04, 09:54 AM   #4
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Try a good solvent. I removed a stuck seatpost for a friend by spraying the inside of the seat tube with PB Blaster. I sprayed it from inside the bb shell and let it sit overnight. A sharp twist with a pipe wrench with a 2 ft breaker pipe over its handle for extra torque popped it right out with no damage to the frame.
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Old 11-12-04, 10:23 AM   #5
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Quote:
Originally Posted by max-a-mill
so i got a piece of aluminum seatpost thoroughly stuck in an older steel frame i just got to try and fix up for my ladyfriend. my big wrench wont budge it.... and it needs to come out!

i heard from someone that it might be possible to melt the aluminum post out by using some sort of chemical??? anyone heard of this madness? or anyother good tips for dislodging a stuck piece of a seatpost?
Before going to destructive techniques, have you tried chemical penetrants like WD-40 or penetrating oils to "dissolve" the bond? Some of the claims on cans of this stuff are pretty bold. Not sure if it will work on aluminum-steel interfaces, but it's worth a try. After the penetrant sits, perhaps try tapping the seat post (in a direction in-line with the tubes) that with a hammer to shear the bond. If you're afraid the seat post will disappear into the seat tube, you can grab the exposed post with a pair of Vice Grips before you tap.

Good luck and let us know what worked.
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Old 11-12-04, 10:26 AM   #6
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Before going to destructive techniques, have you tried chemical penetrants like WD-40 or penetrating oils to "dissolve" the bond? Some of the claims on cans of this stuff are pretty bold...
Ooops, I guess I should've read Shelton Brown's hints first:

"Aluminum seatposts frequently become stuck by corrosion also, and penetrating oil is almost useless against aluminum oxide. Fortunately, aluminum oxide can be dissolved like magic by using ammonia."
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Old 11-12-04, 01:54 PM   #7
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One thing nobody mentioned is how to prevent this from happenning again. Make sure you grease a seatpost when you install it. Grease is (mostly) what will slow down or prevent corrosion in the first place. I know it sounds counterintuitive, but it IS the right thing to do.
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Old 11-12-04, 01:58 PM   #8
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i made it through most of the post with a hacksaw last night in about 45 minutes (my arm is noticably sore today)....

gonna go home and hack some more. someone just mentioned to me that there might be some solvent to melt the aluminum so i fugred i'd float that theory here.

might buy some ammonia too! just gotta remember when cleaning (if we have some left over) to never mix it and bleach together... i made that mistake once already.
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Old 11-12-04, 02:48 PM   #9
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Dont know about you, but I know about Dave Moulton, and for those who dont know, he is a PRO. (Couldnt get more capital letters, sorry Dave ) So, be sure you are atleast a Pro before using the torch on your frame. It will work as Dave suggest, but remember, it sounds easy but thats just because its Dave saying it. Its a bit like Rambo... "Dont try this at home"
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Old 11-12-04, 02:55 PM   #10
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I have had success with drilling a hole thorgh the middle of the seatpost inserting a drift and hitting the drift with a hammer (both axially and radially with regard to the post)
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Old 11-12-04, 03:48 PM   #11
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might buy some ammonia too! just gotta remember when cleaning (if we have some left over) to never mix it and bleach together... i made that mistake once already.
Yeh, chlorine gas - not good ;-(

Hey, anyone know what happens when you mix ammonia with grease ...... like the mixture you (could)end up with in your BB after pouring it down the seat tube for this??? I think if I were doing this I'd be taking a look at that when you finish with the seat post. Just a thought.
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Old 11-12-04, 04:19 PM   #12
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Ammonia wont stay in your BB because it should drain out of the hole in the bottom
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Old 11-12-04, 04:54 PM   #13
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Ammonia wont stay in your BB because it should drain out of the hole in the bottom
Yes, but my question is will it interact with the grease on it's way through? Maybe I'm splitting hairs here, but I had a situation where my BB got squeaky and when I pulled the first cup off about an ounce of water came out. The little hole had got plugged up with corrosion and I don't think this is an unusual occurance.

Really, what I am most interested in is what happens to grease when exposed to ammonia. If I had some ammonia around, I'd go mix up a batch ;-) Sorry about this tangent to the thread.
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Old 11-12-04, 04:59 PM   #14
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Hey Cascade168, take a heap of rust and then cut down a coca-cola can in small squares and set it on fire... Back in the old days it was sometimes used to weld railway tracks, so use a LONG stick to ignite it cause it gets hot
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Old 11-12-04, 05:18 PM   #15
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Hey Cascade168, take a heap of rust and then cut down a coca-cola can in small squares and set it on fire... Back in the old days it was sometimes used to weld railway tracks, so use a LONG stick to ignite it cause it gets hot
I'll bet if you mixed in some magnesium filings with that ..... Now then you'd have something
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Old 11-12-04, 07:08 PM   #16
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I'll bet if you mixed in some magnesium filings with that ..... Now then you'd have something

You would have Thermite which is used to do field welds on railroad track.

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