Mar 12, 2001 2:50 PM
|My brother's syncros (alu) post is mine if i can just get it out of the steel frame its stuck in. (sort of a sword-in-the-stone challenge). He was just on the verge of cutting it off and taking his frame to a machine shop to remove the rest. The post has been siezed for at least a year, and a bike shop has already had a go at it (although i don't know what they tried). Anyone have much sucess at removing severely stuck seatposts?!|
|Some things to try||Kerry irons|
Mar 12, 2001 4:06 PM
|Most of these methods take some time, but it doesn't sound like the bike is going anywhere.
1. Sluice Liquid Wrench or other penetrating oil around the top of the seat lug and then up the seat tube (through the BB with the frame upside down).
2. Wrap the seat post and seat cluster in ice (bags of frozen vegetables work well) until it's frosty cold, then rap a hot, wet rag (right out of the microwave, wear gloves!) around the seat cluster - don't get it on the seat post. Repeat. The thermal expansion may break the bond between the frame and post.
3. Ammonia water (cleaning supplies) applied to post and frame from the inside, like the penetrating oil. Ammonia reacts with aluminum and may break the Al-Fe bond.
While doing these things, brace the frame and give the post some solid whacks with a mallet right were it enters the frame - mechanically breaking the bond. Also, a big pipe wrench on the head of the post (protect the post with thick wrap of rags) may apply more torque than the bike shop was willing to. Could also break the post. Recognize that a seat post frozen for over a year in steel will not look so great when/if it comes out, but it's worth a try.
|One last idea||Retro|
Mar 13, 2001 7:50 AM
|When everything else fails, try clamping the POST in a vise, then turn the frame. You can get more leverage that way than by turning the post (thus twisting the seat tube like a barber pole...).
Like Kerry, I've read that ammonia will dissolve the aluminum/iron corrosion, but I've never tried it. Let us know if it works.
Mar 13, 2001 8:07 AM
|One more thing that I've done. You know the little gap behind the seat tube at the top? Depending upon the size of the gap, find something that will fit in there but now tear things up, and pry it open a little bit, then try to get more lubricant down inside.
|Ammonia and the last resort.....||Mongrel Biker|
Mar 13, 2001 1:16 PM
|.....I been soakin one in ammonia for months and have tried everything else too.Some so creative and potentially destructive, I won't mention them. Am about to resort to the final option of cutting off the post and using a hacksaw blade as per Sheldon Browns article at www.harriscyclery.com. Not looking forward to it as there is 7" is post in the frame and thet's alot of sawing.|
Mar 13, 2001 2:45 PM
|I cant get to work on my seatpost untill tomorrow, but thanks for the suggestions. That sheldon brown site is beautiful. I will check it before posting future messages! |
in the meantime, Im intrigued at the idea of ammonia dissolving the al-fe bond . Any chemists care to elaborate; or even better- draw a balanced equation? My post is anodized black - will this have an effect? Are any toxic gasses produced?
|chemistry challenge accepted||Kerry Irons|
Mar 13, 2001 5:03 PM
|The only gas you will get is a little bit of free NH3 that exists in equilibrium with the NH4OH in the ammonia water. All of the chemistry you are looking at is in solution. Corrosion of a seat post in a steel frame is not about Fe-Al bonds - both are positive charge so they can't covalently bond. You are looking at Fe2O3*(H2O)N (rust is a hydrate) intertwined with AlOx and AlOHx. The ammonia is dissolving the AlOx and AlOHx, not breaking an Al-Fe bond. Since the Al is dissolving, any nicks in the anodized layer may result in some further loss of the black anodization, but the part that is in the frame is going to look pretty bad anyway. How much is this seat post worth?|
Mar 13, 2001 7:55 PM
|And I thought I knew my chemistry. I was gonna break out the chemistry books to try and solve it out of late night boredom but you did a better job than I could have. Oh well. TTFN|| |