or just buy the same saddle again
removing a seized seat post:-Seat posts can at times bond very effectively inside of a frame. This is especially true of an aluminum post and a steel frame. The bond is a result of an exchange of ions between the two materials. You can help prevent this bonding by keeping the post greased where it enters the frame. The various anti-seize materials are also effective and tend to be more resistant to water and corrosion.
When inserting an aluminum post into a carbon frame, it is important to apply a barrier between the two surfaces. This is also true when installing a carbon post into a steel or aluminum frame. A “galvanic reaction” occurs between the two different materials and this acts to eventually bond the post to the frame. Use a light coating of grease, anti-seize, or other lubricant to create a barrier between the two surfaces. It is also a good idea to occasionally necessary to remove the post, clean the surfaces, and the reapply lubrication.
It is sometimes possible to remove the stuck post. However, be aware that there will be cases where the post is simply bonded permanently to the frame.
Begin by removing the post binder bolt entirely from the frame. Mark the post where it meets the frame. This will help track progress as it comes up. Some posts may simply twist side to side, but not come upward.
The bond material is typically of an alkaline base. It can help to use a mild acid to weaken the bond, such as lemon juice or a cola such as Coke® or Pepsi®. Allow some time for the acid to work.
In any case, a penetrating oil or light lubricant is better then nothing. Attempt to twist the saddle back and forth after allowing the fluid to penetrate. If the saddle twists, pull upward and note if any upward progress is being made. The post may eventually heat up from the work, so allow it to occasionally cool off.
If it is impossible to twist the saddle by hand, more leverage may be required. Remove the saddle from the bike. Remove the wheels from the bike. Mount the bike upside down with the post clamped in the hard jaws of the vise. This will allow the frame to be used as a lever. It may be useful to have someone pull upward while you twist the frame side to side. If the post is very tight still, use care not use the rear dropout for leverage as this may bend the rear triangle.
If the post is still stuck, it may be possible to cut the post off and then cut it out of the bike. Cut the post close to the frame. The original post may be cut out completely with a “jab saw.” This is a hacksaw handle that allow cutting inside a blind hole. Cut the post in four places. Use care not to cut into the frame. After cutting, hit the post to collapse it. Remove the pieces. NOTE: Do not attempt to remove a carbon post by cutting it out.
It may be necessary to hone or finish the inside of a steel frame after removing a stuck post. There may be corrosion still inside the frame. It is not recommended to hone or sand carbon frames, however.
If it is a thin-walled post, it is may be possible to mount another post inside the stuck post. The first post becomes a “shim.” You will need to create a compression slot in the back of the post to allow the binder to hold the new and smaller post.
^^lifted from the Park Tool website.
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