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Stuck due to wrong size - no corrosion, just pushed in hard.
Freezing the alu is best option to contact, would this product work as opposed to shit loads of ice?
Following! Just bought a used road bike for my son for commuting, seatpost seized in seattube. Alu/Alu. Seattube flares / widens below the seat/top tube seat stay interface, I can just get it twisting but its not moving up or down.
Try to pull the frame off the post not the post out the frame
Steel is stronger than Alu, so clamping the post in a vice (attached firmly to a workbench), and twisting the frame, might work. Heating the frame with a heat gun/blowtorch could expand the steel sufficiently to free the post. Be careful though. Caustic Soda will dissolve Aluminium but not react with steel, but that's an extreme measure. Another method is to use a hacksaw blade to cut a slot in the post; this should release sufficient tension. Takes bastard ages though.
Don't expect the post to be useable afterwards. As me how I know...
Go onto Insta and look for Stirling Bike Doctor, his account should hopefully still be up, his seat post extractor is a thing of beauty.
TL:DR - clamp the post, brace against the BB and use a headset press to unscrew it. Exactly the same principle as a gear/valve guide extractor but clamped. Needs some fabrication first but will make short work of such jobs.
@configurstion steel expands slower than alu so heat won't help
Stuck due to wrong size – no corrosion, just pushed in hard.
What size are we talking about here?
Minimal difference I hope. Not had eyes on yet
Find someone local with a pipe workstand and clamp the post in and then use the frame to twist and pull the post out.
https://www.screwfix.com/p/rothenberger-tripod-stand-with-6-vice/2390k
https://www.hss.com/hire/p/pipe-vice-and-stand
@squrrelking Stirling Bike Doctor has closed his business sadly, but John at JM Richards in Perth has made a similar post removal tool. He might even sell them to other shops now - he was certainly planning to.
Yorkshire Bike Mechanic
If it's really REALLY stuck, caustic soda will dissolve the alu post to dust and not damage the steel frame at all. Doesn't even mark the paint.
I was sceptical and expecting it to be a messy hassle. It was completely hassle free, just don't rush it.
@configurstion steel expands slower than alu so heat won’t help
Well, I've used this method and so have others, and it does work. You're just heating the outside enough to make the thin walled steel tube expand a tiny fraction. I've also seen the technique used on stubborn BBs.
Another method is to use a hacksaw blade to cut a slot in the post; this should release sufficient tension
I should clarify that the cut needs to be vertical, along the post. It's a tricky job; I used a piece of 18mm or so dowel, with a slot cut along it's length, to accommodate and stiffen the hacksaw blade. A lot more difficult if a lot of the post is in the frame though, although I unstuck a seized post that had about 8" inside the frame.
I was sceptical and expecting it to be a messy hassle. It was completely hassle free, just don’t rush it.
I wouldn't say it's 'hassle free'. Caustic Soda is nasty stuff; protect your eyes and skin. And don't expect it to be quick, as said. Once took me about 2 weeks of repeated daily applications, to dissolve a post enough to free it.
My friend had success with lemon juice of all things after all other liquids failed. Not sure if the other stuff he used started to work or if lemon juice is just a good way to break the bond as its a mild acid.
If you go the caustic soda route be aware that it makes hydrogen gas as a by product. Which means you get to do the squeaky pop experiment you did in chemistry class
@sillyoldman yeah I'm aware he's stopped trading but was hoping his Insta account was still up.
Clamp the SP in a big vice, move frame worked for me after plus gas, hot and cold shizzle didn’t.
Freezing spray on the post sounds worth a try. The aluminium should contract more than the steel, and if you spray just the aluminium it will be colder, so should contract even more. Conductivity of aluminium is good so you may be best spraying the protruding part, otherwise consider spraying down the inside but if the spray overshoots down the seat tube that will cool the steel.