TYGA Posted February 9, 2009 Share Anyone had any experience or knowledge of an aluminium seatpost getting fused into a carbon frame and how to loosen it? Mate of mine was looking at a 2nd hand carbon bike which is in great nick, except the seatpost has been seized solid into the seat tube. I haven't seen the bike so I can't give much info but I assume there is some sort of an aluminium sleeve inside the carbon seat tube. Any comments? Link to comment Share on other sites More sharing options...
Bike Mob Posted February 9, 2009 Share Over to JB... Link to comment Share on other sites More sharing options...
TYGA Posted February 9, 2009 Share OK I have just received an explanation...can anyone back this up? "For some chemical reason, carbon fiber likes aluminum. Aluminum seat posts can run the risk of seizing to a carbon frame, and vice versa. When left in contact for a long period of time, carbon and aluminum will bond together making seat post adjustment difficult if not impossible.<?: prefix = o ns = "urn:schemas-microsoft-com:office:office" /> Carbon bonding with aluminum isn't necessarily common, but it happens. If you're carbon bike has been sitting for a couple of years and you can't adjust your seatpost, hope is not lost. You're probably going to have to pull that bottom bracket out and see if you have a hollow seat-tube (Bianchi is a popular brand which often doesn't). If so, make sure the top end of you seatpost is fully sealed (if not, plug up the hole), get a can of Coke and pour it down the seat-tube and let it sit overnight. Seriously. I don't know much about chemistry, but there is something in carbonated sodas that loosens up seized parts. Just be careful once you get the seatpost to budge that you don't get coke all over the place, and flush it out thoroughly with some sudsy water so you aren't wondering where all those ants are coming from next summer. For the scientific blah blah ... Idealy, you would have a carbon seat post, to prevent galvanic corrosion. The aluminum will corrode because it is the anode with a potential of -1.67, and the carbon the cathode with a potential of +0.81. A difference in potential of 2.48 volts. Where as titanium and carbon both have + potential, and the resulting difference is only 0.755 volts, which is negligible. (Remember kids, that even though both carbon and titanium are both + charges, its the difference in potential that creates a charge. So, something about + and ? charges causing anodizing process. Don?t know if their Coke technique works but hey ? there it is. " Link to comment Share on other sites More sharing options...
Reg Lizard Posted February 9, 2009 Share Don't know if it will work but learn't something from my dad once. I had a rusted gate hinge which got stuck solid. Tried everthing- q20 the works, and the old man rocks up and starts pouring water on it and moving it slowly back and forwards and whala. That hinge still works today- 15 years later. I think the carbon aluminium thingie is a bit different though- its like a welding process that takes place. Link to comment Share on other sites More sharing options...
Ryan Posted February 9, 2009 Share Do you really want to buy a bike that has been so badly neglected? Link to comment Share on other sites More sharing options...
Reg Lizard Posted February 9, 2009 Share OK I have just received an explanation...can anyone back this up? "For some chemical reason' date=' carbon fiber likes aluminum. Aluminum seat posts can run the risk of seizing to a carbon frame, and vice versa. When left in contact for a long period of time, carbon and aluminum will bond together making seat post adjustment difficult if not impossible.<?: prefix = o ns = "urn:schemas-microsoft-com:office:office" /> Carbon bonding with aluminum isn't necessarily common, but it happens. If you're carbon bike has been sitting for a couple of years and you can't adjust your seatpost, hope is not lost. You're probably going to have to pull that bottom bracket out and see if you have a hollow seat-tube (Bianchi is a popular brand which often doesn't). If so, make sure the top end of you seatpost is fully sealed (if not, plug up the hole), get a can of Coke and pour it down the seat-tube and let it sit overnight. Seriously. I don't know much about chemistry, but there is something in carbonated sodas that loosens up seized parts. Just be careful once you get the seatpost to budge that you don't get coke all over the place, and flush it out thoroughly with some sudsy water so you aren't wondering where all those ants are coming from next summer. For the scientific blah blah ... Idealy, you would have a carbon seat post, to prevent galvanic corrosion. The aluminum will corrode because it is the anode with a potential of -1.67, and the carbon the cathode with a potential of +0.81. A difference in potential of 2.48 volts. Where as titanium and carbon both have + potential, and the resulting difference is only 0.755 volts, which is negligible. (Remember kids, that even though both carbon and titanium are both + charges, its the difference in potential that creates a charge. So, something about + and ? charges causing anodizing process. Don?t know if their Coke technique works but hey ? there it is. "[/quote'] Well if you see what else Coke is good for, then it will in all probability do the trick Link to comment Share on other sites More sharing options...
Christie Posted February 9, 2009 Share How about sticking the exposed alu seatpost into some super cold water/ dry ice for a while? Alu should shrink much more than the carbon composite, perhaps it will come loose? Link to comment Share on other sites More sharing options...
Johan Bornman Posted February 9, 2009 Share OK, once you;ve tried all the Coke, Fanta, dry ice, Q20 and water, do what you should have done in the first place. Saw off the seatpost, 5mm above the frame's seat collar. Take a hacksaw blad and saw through the seatpost from the inside of the post. In other words, you are attacking the entire length of the remaining post at once. Be patient, work in good light and take frequent breaks. Don't get impatient. Watch out for black, rather than silver filings and stop if you see the former, carry on sawing if you see the latter. Once you're through, you grab the seatpost with a strong set of pliers by the corner of your fresh cuts and roll it inwards like opening an old-fashioned sardine can. Apply the force in such a way that the roll goes inward and doesn't just become a small little roll at the top. Before you've rolled halfway the post will come out. Nowadays they make special saw handles for this type of job. Go look at your hardware centre. In my day we did it with a naked saw blade held between our teeth because our hands were so blistered and bloodied. You young guys have it so lucky.... Why chemicals don't work. The post forms a near perfect seal with the seat tube. The area that the coke can reach is effectively just a little ring at the bottom or top of the post. It cannot penetrate or, penetrate in sufficient volumes to do any good. The aluminium oxide crystals are large and crusty and cause the post to effectively swell. It does't weld, just swells and that's why it easily comes out once you've sawn through and winded it up a little bit. Once youv'e got the errant post out, you'll notice that it was greased. Grease is evil. Now that you have it out, now put it in coke and see if the crystals dissappear. Let us know. Link to comment Share on other sites More sharing options...
TYGA Posted February 9, 2009 Share Thanks Johan, that sounds like the kind of job you attempt BEFORE you hand over the cash for the bike! Link to comment Share on other sites More sharing options...
slowtwitch Posted February 10, 2009 Share I've got the same problem with my Alu frame and post - the bike is only 1 year old and NOT NEGLECTED Bike shop rekoned Q20 a couple of days and "work it". Well that aint doi'n notingI'll first try the coke - bb- thing - but also read before from an experienced mechanic that in the end you always bring out the hacksaw Link to comment Share on other sites More sharing options...
slowtwitch Posted February 10, 2009 Share I've got the same problem with my Alu frame and post - the bike is only 1 year old and NOT NEGLECTED Bike shop rekoned Q20 a couple of days and "work it". Well that aint doi'n notingI'll first try the coke - bb- thing - but also read before from an experienced mechanic that in the end you always bring out the hacksaw Link to comment Share on other sites More sharing options...
paulvs Posted February 10, 2009 Share now how about whne you need a seatpost shim between your carbon frame and alu post... what would we go for??? Link to comment Share on other sites More sharing options...
Shebeen Posted February 10, 2009 Share Johan, out of interest how many times have you personally done this? Seems like both a tedious and complicated job. How many hours does it take, and does it always work? Link to comment Share on other sites More sharing options...
Johan Bornman Posted February 10, 2009 Share Johan' date=' out of interest how many times have you personally done this? Seems like both a tedious and complicated job. How many hours does it take, and does it always work?[/quote'] I have done it three times. All three times it was a Cannondale frame. Either my own or my wife's. I have had two alu seatposts freeze on mine and one on her's. I've also had two 3TTT stems freeze inside my Cannondale's steerer. I've operated on the first one and the second one is still on my bike, still frozen. I'm just waiting for an evening when TV is really bad and then I'll tackle the stem. I solved the seatpost problems by going Titanium on the seat post. I solved the problem on my wife's frame by her no longer riding bike. I removed the seatpost and put the frame in the garage rafters. Since then it has not given me a day's trouble. If you think this is not a tried-and-tested way, trawl the 'net, trawl Google Groups, trawl the chat groups. You'll see lots of advice on this or that chemical but will not find a single example of it actually working. It is neither tedius to do nor complicated. It is just heartbreaking to saw through a R700 seatpost. With a bit of patience you'll have the job done in 45 minutes. Buy one of those hacksawblade handles made for holding the blade without a frame. It looks like a Stanley knife with the brade protruding from the front. I'm sure it'll make the job much, much easier. I just wrapped a bit of cloth around a blade. Work in good light and don't be impatient. Don't saw the post off flush, leave 25mm above the frame for the pliers to grip. Link to comment Share on other sites More sharing options...
slowtwitch Posted February 23, 2009 Share Feedback on the coke-bb-soluton: DID NOT work on my Alu frame and post PS tried Q20 as well without success..hacksaw here I come Link to comment Share on other sites More sharing options...
Johan Bornman Posted February 23, 2009 Share I would have been very disappointed in my own experience if Coke did work. Still, it's still to have some ice cold Coke with you when taking on this job. If I can emphasise just one point it'll be PATIENCE. Johan Bornman2009-02-23 03:33:48 Link to comment Share on other sites More sharing options...
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