Recently I tried to adjust the seat height on my Ti Serrota and discovered that the seat post was frozen in the seat tube. I was able to rotate the seat post about 10 degrees to each side but that required a significant amount of force. The seat post is aluminum. Any suggestions on how to best go about loosening the seat post?
You likely have some galvanic corrosion going between the Ti and aluminum.
start with trying to get some penetrating oil down the seat tube. Let it sit for 24 hours and see if it breaks free.
It may take multiple applications. If that doesn’t work, you’ll need to take more drastic actions that will likely require sacrificing the seatpost. But cross that bridge when you get to it.
If you can move the seat post it requires repeated twisting and pulling up which will get easier as it frees up and post extends.
Swap your nice saddle for an old one or just rails then you may be able to get a ring spanner onto it to twist the post more easily. As far as pulling goes, sit backwards on the top tube and wrestle it.
Or put the post head in a vise and then use the frame as a lever to get it twisting.
There are homemade presses that clamp the seat post and bottom bracket to pull out totally stuck posts (see YouTube), but those are probably not needed here.
A Coca Cola treatment to dissolve the seat post is also possible, (Ti is used in chemical plants for stuff a lot nastier than cola so the frame will be fine) but I’ve never tried this as I had carbon posts or aluminium frames.
I’ve applied penetrating oil and am waiting for it to work down the seat tube. I fully expect to need to apply more. I’ve also used an adjustable wrench with a 12 inch long handle to clamp the top of the seat post under the seat to supply leverage to twist the seat post. I haven’t yet tried the vice approach but that may come next.
Bike mechanic here. The other posters are 100% correct. If it’s moving a bit, the job will be easier. Just keep working it. If you have a spare fork mount block like you’d use in a van or pick-up, it’s a good way to anchor the front of the bike. Bolt it to a board and park your car on it. I have one bolted to the base of my stand at work. A lot of seatposts have the saddle clamp bonded on to the shaft. It’s a male-female interface with the saddle clamp typically being the male half bonded into the female shaft of the post. Grabbing the saddle clamp with a large adjustable or bench vise can rip the clamp off of the post, so be careful you don’t fall over backwards if it suddenly breaks free. A large pipe wrench will grab the post. They’re fairly inexpensive at places like Harbor Freight, so that’s an option if you rip the saddle clamp off the post. I’ve also had luck drilling a hole in the post and inserting a 3/8” -ish diameter rod to use as a T-handle for twisting leverage. Lastly use some cardboard or old towels to protect the frame around the seatpost clamp area. If a heavy adjustable wrench or pipe wrench suddenly pops off the post, the tool is going to clank down on the frame and damage it. I dropped my 24” adjustable on a customer’s Ted Wojcik this way. Both of my hands were way out on the end of the handle like how you’d hold a baseball bat and my feet weren’t under me. The wrench jaws came off the of the saddle clamp and landed on the seatstays.
1 Like
If you remove the crank and BB, you can also spray penetrating oil down the seat tube if you flip the frame upside down. This can help getting more penetrating oil into the seat tube.
you can also try Coke to break the seatpost free, but it won’t dissolve the seatpost, just help break up the corrosion. I mean Coke is not great for you, but it isn’t gonna dissolve a seatpost. 
Oil wont dissolve the corrosion but will reduce the friction when moving the seatpost. To my knowledge, the corrosion is equivalent to an oxidation of the metal and a resulting formation of salts. If both metals (seatpost and frame) corrode, the salts could integrate into each other, kind of bonding. In any case, the formed salts will have a larger volume and therefore act like and expansion bolt.
Optimally you shouldmdissolve the corrosion, the salts, without damaging the metals. I dont think that is possible and will be impossible to get sufficient amounts of acid to the location of the corrosion, flushing would be necessary (wash away used acid, apply fresh).