One of the best ways to ruin your bike frame is for your seat post to become stuck in the seat tube otherwise known as a stuck seat post. In this article, I am going to show ways of getting a seat post loose.
AN OUNCE OF PREVENTION IS WORTH A POUND OF CURE!
The best way to get a stuck seat post out is to not get it stuck in the first place. Simply liberally apply some grease on the part of the seat post that is hidden in the seat tube. Do this at a minimum once a year and more often if you ride in rain and snow. This will prevent this from ever happening. Note: If you have a carbon fiber bicycle or carbon fiber seat post, do not grease it. Grease can break down carbon fibers, but you should remove it and reinstall it regularly to make sure there is no corrosion or bonding between the frame and the post.
STUCK SEAT POSTS
So you or someone else did not heed the above advice and now have a stuck seat post. Bicycle shops abhor the mention of a stuck seat post. Many will not fix them and even for those that do, it will be a costly repair due to labor costs. There are several do-it-yourself methods that you can use and almost all of them include huge amounts of time and patience. Also, make sure that you use eye protection, proper gloves and in some cases respiratory protection to do some of the repairs listed here. Any repairs should be done at your own risk and neither the author or Smile Politely can be held liable if you attempt repairs beyond your skill level. If you're not sure, take it to a professional!
First off, leave the seat on the bike or, better yet, find a disposable seat in bad shape (we always have plenty of these at the Bike Project) to put on the post if you value the current seat. Things could get ugly. One note: do not cut the seat post till you have exhausted all of the following methods.
The first method is to spray some kind of penetrating lubricant such as WD-40 or better yet, PB Blaster into the area where the seat post is stuck into the top of the seat post tube. Bicycle mechanic guru Lennard Zinn also suggests that Coca-Cola (regular, not diet) might work as well. You also might want to remove the cranks and bottom bracket, turn the bike over and spray on the other side of the seat tube as well. Use the lubricant liberally so that it soaks in. Then wait.
After a period of time, try and twist the post by torquing the seat back and forth to see if you get movement. It is best if you have a buddy help you hold the bike and you try this with the wheels on the ground, as you will get more torque that way. If you have an old junk seat, install that one so if you pound and beat on it, it won't matter. If you are lucky, the post will break free. You should try this several times and even give the penetrating lube a day or so to work free. This method usually works best if you have a steel seat tube and a steel bike. Steel on steel corrosion usually will break free eventually with enough lube, time and torque on the seat post.
HEAT AND/OR COLD
When you add aluminum to the equation, it becomes a bit more complicated. An aluminum to aluminum bond or steel to aluminum bond may not break free with the penetrating lube. The bad news is, for bikes manufactured in the past thirty years or so, there is a good chance one of the components (either the seat tube or frame) will be made of aluminum. The next step is to use either heat or extreme cold to expand or contract one of the tubes enough to break free the corrosive bond. Use a hair dryer, a heat gun or torch (be careful not to remove paint) or empty a complete CO2 cartridge or use ice. Please note that often, when the bond breaks, it will do so with a loud pop, but not always.
AMMONIA AND LYE
You can always also use industrial strength ammonia to break the steel/aluminum bond. Use the 10 percent janitorial strength, not the household stuff. I have also heard that you can use lye, but that stuff is so caustic that I am not sure it would be worth it to take the risk. No matter what, use protection and do it outside.
The more expensive option is to find a machine shop and have them ream out the seat tube, but this is only an option with a cylindrical tube.
ARE YOU HACKED OFF YET?
If the frame is not worth the expense to have it professionally repaired, or you are just too damned cheap (like me, anyway), you can try this method as a last resort: Take the post off to about an inch or two from the top of the frame with a hacksaw (pictured, right). Then, cut wedge shaped pieces out of the seat post and pry it out. Then you can get the remainder out by curling and working increasing amounts of the post out. This is a time- and labor-intensive process. I did say it would take patience, didn't I?
Good luck and keep your seat posts and stems lubed.
Sources and places for more information:
Lennard Zinn — http://velonews.com/article/11799
Sheldon Brown — http://www.sheldonbrown.com/stuck-seatposts.html