I finally stopped procrastinating and got that seatpost out of my '01 Burley Rumba tandem.
I first tried wicking in some Three-In-One into the seat clamp lip and mounting a crappy old seat to it, jamming a handlebar through the rails in that seat, and twisting the handlebars with all my might. This ended up turning the seat clamp, which is not welded on but bonded on. Then I tried wicking in some PB Blaster and pouring a teakettle of hot water on the joint. I also tried using a very large adjustable wrench directly on the rectangular seat clamp, but I figured this was destined to fail also because the seat clamp would spin. I tried using a pipe wrench to grab the seatpost itself under the seat clamp, but it seemed to just chew into the aluminum and I didn't trust it to not tear too much material off the post. (At this point, I still wanted to try to save the post.) I was able to see the post shifting a bit at the top of the clamp area, squeezing out fluids as I twisted, but still didn't seem to budge. I then used a flat-blade screwdriver to pry the seat tube ears apart a bit at the seat clamp, and tried dripping ammonia in, and then tried taking out the bottom bracket with idea that I'd flip the frame upside down and flood the entire seat tube with ammonia overnight. That was a bust because the beautiful Burley frame has sealed-off tubes at the bottom bracket shell. I couldn't do this trick through braze-on boltholes either, because there are none on the seat tubes of this frame.
Then I tried mounting the seat clamp in my small bench vise and twisting. I used a heat gun to try to expand or shock the materials. I know I should have tried freezing the seatpost as well as heating the seat tube with a heat gun, but we didn't have any ice at our disposal. In any case, this broke my bench vise. Then I tried mounting it in a large bench vise andand twisting. This, caused a "pop", but as I suspected, the pop was not what I wanted -- it was just the seat clamp spinning in its post again, like it did with the handlebar. I can't say I didn't expect this would happen. At this point I considered taking the frame to an auto shop to let them try the air hammer trick (Lennard Zinn's step 6)
, but I was on a roll and figured I didn't care to save the seatpost, so now I tried mounting the cylindrical post part itself in the vise to try John Allen's step 6. This didn't particularly deform the seatpost -- the seatpost clamp's post jammed into the top was almost entirely olid aluminum -- so the twisting just caused the seatpost to spin in the vise.
Now I was ready to cut the seat clamp off. I started with a hacksaw, then got tired and finished with a bandsaw.
The idea was to get the seat clamp collar and tandem stoker handlebar stem off, so that I could squeeze down unencumbered with the vise and try to get a better purchase of the vise on the seat post by hopefully deforming it a bit (John Allen's step 6)
. The metal where the clamp was and was still bonded into the top of the post was so thick that no amount of squeezing the vise seemed to deform the tube, and the tube just spun again. At this point I used a bench grinder and a hand file to grind two flats on either side of the seatpost, and mounted that in the vise again. Now the vise seemed to really grip.
So now I heated the seat tube with the heatgun (still no ice for cooling the post), and with the help of a couple of friends, we twisted rapidly back and forth from further and further out towards the end of the frame for more and more leverage, and it finally started to move. We took turns giving it a good ten to fifteen minutes of athletic twisting while pulling, and it was out, about a millimeter per minute up until the end when it just started coming out much faster.
The new seatpost is steel, and it's a smaller diameter than the tube, with a shim to get it back to 26.6mm. I suspect this will be less likely to get stuck, simply because less of the metal is making direct contact with the smaller-diameter seatpost. In any case, I greased the hell out of it now so it better not happen again.