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Tech FAQ: Stuck Seatposts Suck

  • By Lennard Zinn
  • Published May. 18, 2010
  • Updated Oct. 11, 2012 at 5:13 PM EDT

Dear Lennard,
My seatpost is stuck in my frame and I’ve tried everything! It just won’t come out! I soaked it for days in Knock ‘Er Loose penetrating oil, and I broke the saddle rails banging on the saddle with a hammer trying to get it to budge, but to no avail. It’s a Ritchey Pro aluminum seatpost in an old steel hardtail. Please help.
-James

Dear James,
Penetrating oil does not dissolve aluminum oxide very well. But you probably have figured that out by now. Here’s how you for sure can get that post out:

1. Remove the seat binder bolt. Slide the binder collar up the seatpost. Easy enough.

2. Squirt ammonia around the seatpost and let it sit overnight. Ammonia dissolves aluminum oxide, and automotive anti-freeze or cola (yes, the soft drink) often will as well; penetrating oil will only work with a steel seatpost in a steel frame. To get the most penetration, remove the bottom bracket, turn the bike upside down, pour ammonia, anti-freeze or cola in from the bottom of the seat tube, and let it sit overnight.

3. Stand over the bike and twist the saddle.

4. If step 3 does not free the seatpost, use thermal expansion/contraction. The idea is to get either the seatpost to shrink and pull away from the seat tube, the seat tube to expand and pull away from the seatpost, or both. But you must be aware of the relative Coefficient of Thermal Expansion (CTE) of the materials the seatpost and seat tube are made out of. The CTE of aluminum (and of magnesium) is about double that of steel, and the CTE of carbon is almost zero.

(a) So if you have a carbon-fiber seatpost stuck in a frame made out of any of these materials, warm up the seat-lug area with a hair dryer (or even a heat gun or torch, if you’re careful) to expand it.

(b) Or if you have an aluminum seatpost stuck inside a carbon or steel frame, cool the seatpost down. If there is a big enough hole from the bottom bracket shell into the seat tube after you’ve removed the crankset, drop small hunks of dry ice in, and let the post get really cold. From the outside, discharge the entire cartridge of a CO2 tire inflator at the joint of the seatpost and the seat collar to freeze it and shrink it. (Alternatively, ice the exposed seatpost with a plastic bag filled with dry ice, or get your hands and your seatpost on some liquid nitrogen.)

(c) If both parts are made out of the same metal, you can still try to cool the post rapidly while you heat the seat lug in hopes they’ll shrink and expand in opposite directions.

(d) Now try twisting as in step 3.

5. If step 4 does not free the seatpost, you will need to move into the difficult and risky part of this procedure.

(a) Clamp the top of the seatpost into a large bench vise that is bolted to a very secure workbench. Remove the saddle and all of the clamps from the top of the seatpost first, and turn the bike upside down above the vise. You have just ruined your seatpost. Don’t ever ride it again.

(b) Perform the thermal expansion/contraction trick from step 4.

(c) Grab the frame at both ends, and begin to carefully apply a twisting pressure. Be aware that you can easily apply enough force to bend or crack your frame, so be careful. If the seatpost finally releases, it often makes such a large “pop” that you will think that you have broken many things!

6. If that did not work, you can take the bike to a car repair shop. Ask a mechanic to smack the underside of the seatpost clamp with an air impact hammer. If it works, it will take seconds and won’t damage the frame. Be forewarned that it’s loud and violent, though.

7. If step 6 fails, cut off the seatpost a few inches above the seat lug. There are a number of things you can try now.

(a) Warm up the seat-lug area with a hair dryer to expand it. Discharge the entire cartridge of a CO2 tire inflator down inside the seatpost to freeze it and shrink it. Now clamp what’s left of it in a vise and try twisting as in step 5.

(b) Get your hands on a slide hammer; borrow or rent one from auto-body-related businesses. This is a tool for pulling dents out of car bodies and consists of a long rod with a heavy cylindrical weight (5-pound is a good size for this) that slides along it. The end of the rod can be attached to what you are pulling by a number of means, and when you rapidly slide the weight toward the handle, it pulls the whole rod forcibly in the direction of the handle when it hits it. To attach its end to your seatpost , you can either clamp vise-grip pliers to the post or drill a transverse hole through it. Assemble the slide onto the slide hammer rod and attach its end of the to either the pliers with clamping jaws or into the holes via hooks that point inward toward each other. Have someone hold the frame (the inertia of the frame makes it easy to hold onto even when you are in the act of freeing the post), and slam the weight toward the end away from the frame. Chances are, it will pop right out.

(c) Drill a half inch hole transversely through the seatpost, insert a long steel rod through it, have somebody hold the frame, and twist on it as hard as you can. It will make a huge noise if it comes free.

8. If it’s still not free, both of your alternatives stink.

(a) You can go to a machine shop and get the remaining seatpost reamed out of the seat tube, but the chances of the shop managing to line everything up perfectly so the cutter does not make a hole in the seat tube are not good.

(b) Your other alternative is to cut the remaining seatpost out yourself, by hand. You should really sit down and think about it for a while and proceed carefully, since there is a risk of completely trashing your frame. Here’s how you do it:

9. Cut your seatpost off a little more than an inch above the seat lug on your frame. Use a hacksaw.

10. Remove the blade from the saw and wrap a piece of tape around one end. You’re making a handle with which to grab it.

11. Hold on to the taped end and slip the other end into the center of the post.

12. Carefully (very carefully) make two outward radial cuts about 60 degrees apart. Your goal is to remove a wedge from the hunk of seatpost stuck in your frame. Be careful, as this is where many people cut too far and go right through the seatpost and into the frame. Of course, you wouldn’t do that, now would you?

Much faster, but also more dangerous, is to use a reciprocating hand-held jigsaw with a long blade for wood. It will go through an aluminum seatpost very quickly. The question is, what will it do to your frame? On a steel or titanium frame, the wood blade may only polish the inside of the seat tube where it hits it. It will probably go through a carbon, aluminum or magnesium frame just as easily as it goes through an aluminum seatpost, though.

13. Work the remaining piece out. Once you’ve made the cut, pry or pull this piece out with a large screwdriver or a pair of pliers. Be careful here, too. A lot of overenthusiastic home mechanics have damaged their frames by prying too hard here. Curl in the edges with the pliers to free more and more of it from the seatpost walls. It should eventually work its way out.

14. Final alternative: dissolve the seatpost. If you happen to be someone with access to it, a metal like gallium that is liquid at near room temperature will dissolve aluminum. But if the frame is aluminum, it doesn’t help you. And whatever the frame is made out of, you’d better get a chunk of that material and put some of the liquid metal on it first to see what happens before you go near your frame with it.

Now, once your seatpost is out of the frame, take your seatpost out and grease it every once in a while. Drain the water out of your frame overnight while you’re at it.

You don’t want to have to do this again, do you?
-Lennard

Readers can send brief technical questions directly to Lennard Zinn.

Technical writer Lennard Zinn is a frame builder (www.zinncycles.com), a former U.S. national team rider and author of numerous books on bikes and bike maintenance including the pair of successful maintenance guides “Zinn and the Art of Mountain Bike Maintenance” – now available also on DVD, and “Zinn and the Art of Road Bike Maintenance,” as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.”

Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn.

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Lennard Zinn

Lennard Zinn

Our longtime technical writer joined VeloNews in 1987. He is also a framebuilder, a former U.S. National Team rider, and author of many bicycle books, including Zinn and the Art of Mountain Bike Maintenance and Zinn and the Art of Road Bike Maintenance, as well as Zinn and the Art of Triathlon Bikes and Zinn's Cycling Primer: Maintenance Tips and Skill Building for Cyclists. He holds a Bachelor’s degree in physics from Colorado College. Readers can send brief technical questions to Ask LZ.

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