Stuck seat post driving me crazy!

[superdave]

I recently picked up an old cromoly frame mountain bike (an '87 Mongoose Altus) to use for my next ebike project. I figured the strong frame and big triangle (nice horizontal top tube) would make it an ideal donor, and I like the fact that it's a bit of a classic (Mongoose was a pretty respected brand before Pacific Cycles bought it). Plus, it was almost free The bike was in fair condition (for being 25 years old); complete original components and a good solid frame. Disassembly went fine - cantilevers were pretty seized, but some liquid wrench and brute force solved that problem. Then I got to the seat post. I expected it to be seized (I've seen them seize in bikes only a couple years old) but figured "how bad can it be?" I found out!

I started by filling the seat tube with ammonia and letting it sit for 24 hours hoping the acid would loosen things up. I put my 36" pipe wrench on the exposed post and gave it a good pull ... nothing. Perhaps not enough force. Went at it again with as much force as I could muster. I could feel the frame flexing (good thing it's steel), but the seat tube held fast. Plan B involved emptying a can of R134A onto the post to cool it down. Since Aluminum shrinks twice as much as steel when cooled, I though that would surely do it. Nope, big pipe wrench still wouldn't budge it. On to Plan C. I got some pure sodium hydroxide (lye) powder and mixed up a 50% solution. Sodium hydroxide is harmless to steel, but when combined with water it will react aggressively with aluminum. Three treatments, 36 hours, and a garage filled with hydrogen gas later I figured enough material would be dissolved to loosen the seat post. No such luck -- still just as stuck.

At that point, I sawed off the top of the seat post to see how much material was left. I was stunned to discover that instead of an aluminum pipe, I was dealing with a casting with an inside diameter that tapers down to a mere 10mm near the top (and that's after three days of NaOH treatment). So I now realize I'm dealing with 25 years of galvanic welding on a seat post with enough aluminum to support an elephant New plan is to break out a pack of hacksaw blades and start sectioning the post from the inside along it's length so I can chisel/pry out the sections (and hope that after one or two the rest of it breaks loose).

Let my experience be a warning to folks looking to use older bikes for ebike projects -- many problems on a bike can be pretty easily fixed, but a stuck seat post is not one of them.

 

[Ypedal]

getting it apart, easy, getting it apart without destroying it... not always .......

 

[Chalo]

Helpful hints:
http://sheldonbrown.com/stuck-seatposts.html

Tales of horror:
http://www.yellowjersey.org/goodn.html

At my shop, we usually soak the interface with PB Blaster or Deep Creep, leave overnight, and get medieval the next day. When all else fails, we have to send the frame to a machine shop to have the post reamed away.

If you have a nice seat on the bike, replace it with a ratty seat that you can use as a disposable handle for applying hurt. If you can get it to budge, it will come out. Keep applying penetrating lube and racking it back and forth.

And remember to keep it greased!

Chalo

 

[winkinatcha]

Holy crap, just went through Chalo's horror story link... As soon as it is light enough outside, I am going to regrease all my seat posts/headstems!

I have pulled apart a lotta bikes (compared to the average bike fiddler, would be nothing compared to the long term bike fitter proffessionals) and yet to hit this stuck seat post thingy personally... I have obv been one lucky dude.

On an unrelated note, I received a set of bicycle oriented taps yesterday... I now own my first ever left-handed thread tap (for left hand cranks) and used it to recut a Left peddle crank eye yesterday... after getting the angle right I found it quite a challenge to get my head to enable me to recut the thread the "wrong way" (almost had to do it with my eyes shut, after 40 years of bush mechanicing primarily with r/h threads...)

Joe

 

[superdave]

Grease is better than nothing unless you have a CF setpost or frame. Oils often cause laminates to swell -- creating a problem instead of preventing it.

When I finally get the old seatpost out, I'll be using Permatex anti-seize compound on the new one:

That stuff is amazing for protecting steel + aluminum from galvanic welding. I've used it for years on spark plugs and exhaust manifold bolts that thread into aluminum cylinder heads. Even after years of use, the plugs/bolts come out like they were put in yesterday.

 

[winkinatcha]

^^ +1

Thanks

Joe

 

[Punx0r]

Can you drive it down a fraction with a large hammer? It may be all it takes to break the corrosion bond. I only suggest it because it works on seized bolts/studs (smack the end with a hammer).

 

[cal3thousand]

I would try "freeze-off" by CNC. It's like the other bolt removers in that it creeps and wicks into voids, but it also has the benefit of freezing the joint. This shock may be enough to break the surface bond.

 

[Ypedal]

Can you drive it down a fraction with a large hammer? It may be all it takes to break the corrosion bond. I only suggest it because it works on seized bolts/studs (smack the end with a hammer).

That was my first thought.. but obviously this puppy is in there.. real good.. but it is easier to hammer something in vs pulling something out or twisting... once you get it to budge it's all yours......

does the post appear bent ? ( from heavy assed rider abuse )

 

[TylerDurden]

Ugh, that galvanic bond is the biatch.

I'd drill out enough to get a sawzall blade in there and cut it into pie slices: 1, 180, 90... then get the thin chisel workin.

 

[waynebergman]

I have just recently spent a good 10 hours of labor on the same problem with my Giant DH & several sleepless nights looking for a solution to the same problem. I my favor was a seat tube shim going from the bikes internal seat tube to the seat post diameter so I had a bit of a spacer between the seat post and the frames seat tube. I used a reciprocating saw with a long blade and cut the tube into quadrants from the inside of the seat post, being very careful not to cut into the frames seat tube.First move is to cut the seat post tube off about one inch higher than the frames seat tube so you have some material to pipe wrench things with during the cut and twist process. Make sure to find a socket or something you can slide down inside the top part of the seat post tube to stop it from deforming when you wrench it with the pipe wrench. If you don't have something solid inside the hollow seat post tube like a tight fitting socket or something(what is nice about a socket is they step up in small increments till you get the right fit) and you try and put a pipe wrench on it you cant twist it out. I used a metric socket that had a snug fit to the inside of the seat post tube and then suspended it into the top portion of the seat post tube with an old quick release from a rear wheel. The stop on the quick release held the socket from dropping to the bottom of the frames seat tube and the leaver handle gave me something to hang onto if it did slide down in there so I could retrieve it. I used a torch on the frames tubing and squirted in liquid wrench and cut with the recipricating saw and twisted with the pipe wrench etc for ever but it finally came out. GOOD LUCK MAN. I don't know if you are the praying type but I would not try this again with out a set aside time of reflection and asking for some help from above.

 

[wesnewell]

Penetrating oil of some kind left for a few hours or days. WD-40 works good, as does dot 3 brake fluid, which is a lot cheaper. I've freed many a stuck computer fan with a drop of brake fluid on the bearings.

 

[StudEbiker]

Kroil.

http://www.amazon.com/Kano-Aerokroil-Penetrating-aerosol-AEROKROIL/dp/B000F09CEA/ref=sr_1_2?ie=UTF8&qid=1346306397&sr=8-2&keywords=kroil+penetrating+oil

 

[superdave]

Four hacksaw blades and a very sore shoulder later ... Victory!



Cutting out a section along the full length of the post did the trick. Though even with the section removed, it took the 36" pipe wrench to get enough torque to break it loose. Once I got movement, I was able to use penetrating oil and vice grips to gradually work it out. From the looks of things, the lye soak would have worked eventually. Three days of that did dissolve quite a bit of metal from the bottom end, which made it easier to hacksaw through.

My experience with various penetrating oils is that they give amazing results on corroded steel-to-steel, but won't touch a galvanic weld. In this case, nothing short of reducing the diameter of the seatpost (by either chemical or mechanical means) was going work. It didn't help that a previous owner had lowered the seatpost to where the decorative flutes were below the top of the seat tube -- perfect for collecting moisture in the place where you least want it.

The good news is that the handlebar stem saw what happened to its kin and decided to release its grip on the steering tube without me even having to pick up a hammer Now I can get to the real project -- fabricating the battery mount.

 

[winkinatcha]

Wooooh! Success! Well Done mate... Keep this up and your shoulders are gonna be HUGE!

Joe

 

[marty]

Idea from Marty.
Clean the inside of the seat post tube with a tooth brush, hot water and soap. Rinse. Let it dry. Find a cork that is a tight fit inside the seat post. Push the cork till it is close to the bottom of the seat post. Find a large bolt that easily slides into the seat post. Make some groves in the threaded part of the bolt with a grinder. Clean the bolt. Glue the bolt inside the the seat post with some slow drying good quality epoxy glue. Doctorbass epoxy is good. Bolt head should extend out the top of the seat tube.

Spray with penetrating oil, tap with hammer. Repeat every 6 hours for 6 days.

Get a 1/2" drive socket that fits on the bolt. Use a impact wrench to turn the bolt. Try forward and reverse. If that don't work? Turn the air compressor pressure all the way up. If that don't work? Spray with penetrating oil, tap with hammer. Repeat every 6 hours for 6 days. Try impact wrench again.

If you have access to really hot water? Burn your skin temperature. Try spraying the stuck area to heat it up. Then more penetrating oil, tap with hammer, impact wrench.

I am big believer in big impact wrenches. The tic, tic, tic, tic, tic, tic, tic, tic, tic, tic, tic, tic, gets stuck stuff unstuck.

 

[amberwolf]

I feel your pain....

I have a steel seatpost I will eventually ahve to remvoe from a freecycled frame for a project...It's rusted in there pretty good so I expect it to be quite the challenge. I have tried various penetrating oils and combinations of petroleum producs includign ATF and brake fluid over the last couple of years, and it never did anything. I tried tapping it down with the sledgehammer, and only succeeded in denting the top of the seatpost a little.

Eventually I expect I will have to try the sectioning method, or just give up on the frame--it's not really worth the effort anyway (especially since when I started the project, the point was to get the seatpost itself out to use it on a different bike...that is obviously not gonna happen).

 

[superdave]

Amberwolf, if it's steel-in-steel, heat + penetrating oil is your best bet. Since the tube and post have the same coefficient of thermal expansion, the tube will expand slight more than the post. Not enough to make it loose, but enough to let the oil work in between where it can work its magic on the rust. If you're not in a hurry, once a day (the oil needs time to work) for 2 - 4 weeks will likely do the trick.

If it's steel-in-aluminum, good luck. Heat is probably still your best bet as the Al will expand at twice the rate of the steel. That might be enough to break the galvanic weld, but I doubt it. I can't imagine trying to hacksaw through a steel tube from the inside It was painful enough on relatively soft aluminum.

 

[amberwolf]

Steel in steel, both cheap stuff. I've left it out in the direct sun for heating, applying oil as I do so, but it never appeared to have any effect. I have a camping-gas canister and torch head, if that amount of heat is necessary, but it is not worth the expenditure of gas to do this more than once, given my limited budget to get more.

 

[The fingers]

A body shop type slide hammer/dent puller might help, if it can be attached to the post somehow. Glad you were able to get it out.

 

[superdave]

To understand why there are so few good mechanical solutions to the stuck seatpost problem, you need to look at the math. Let's say I can put a constant 100 lbs of force on the end of my 36" pipe wrench for a total of 300 ft lbs of torque. At the seat tube/post interface that's a force of about 7200 lbs. Seems like a lot but when you divide it by the surface area (let's say 31.4 sq in for a 1" x 10" post) you're only looking at 300 psi shear. Doesn't matter whether you apply the force as torque or with a hammer (in either direction), it's nearly impossible to get to a sufficient level of shear force without destroying the frame in the process.