Folks, this is 2023, and stuck posts aren't the nightmare that they used to be.
Muriatic acid dissolves aluminum.
Alkali solutions embrittle steel.
Some of us have found that cutting off 1" above the opening and using a slender, sharp sawzall blade can get any stuck alloy post out fast, with
no damage to the frame.
The tricks are:
1) Begin by probing with a bent spoke to determine the inserted length of the post.
2) Make certain (by means of probing with a sharpened bent spoke) that the slot in the post is cut
through to the steel all the way to the bottom of the post.
3) Do
not align/clock the cut with the slot in the lug.
4) Do
not let the blade contact the edge at the lug opening, so keep the blade's cutting side tilted slightly at all times.
5) Make
sure that the end of the blade can't/doesn't reciprocate/travel too high and thus "catch" above the upper end edge of the seat tube, remembering that the
directional teeth will tend to try to push the saw and blade upward as the blade digs into the aluminum and reciprocates through it's perhaps 1" of stroke.
6) The cut height doesn't need to extend much above the height of bottom of the slot in the seat tube, and doesn't need to extend to the end of the seat tube.
Please read the above (5) instructions several times, slowly.
Be patient and controlled with the cutting, especially when starting out, and again when extending the cut to just barely above the height of the lower end of the slot in the frame's seat tube.
If the teeth out near the tip of the blade clog, or seem to become dull, they can be directionally sharpened using a Dremel "wafer" disc using good technique. The leading teeth should do all of the cutting. Cutting oil on the teeth recommended, any oil will do.
Once cut through to steel, the post can be easily twisted out. For heavier amounts of twisting force using plumbing pliers, put a reinforcing insert such as a dowel into the ID of the end of the post. Back-and-forth action and WD40 should make this easy.
I've had to "slenderize" a Sawzall blade on the bench grinder to cope with the narrow ID of the post.
I've had to sharpen the teeth at the tip of a used blade.
There is no tendency for the blade to dig into the steel, unless you let the teeth contact the
edge at the opening or at the slot.
It takes a lot of concentrated pressure to get a Sawzall blade's teeth to even
start digging into
steel, which is pretty much impossible to achieve at the tip of the blade.
