Today, I asked a colleague to lend a hand. We were just causing the vise to twist in its mount. So my colleague pushed against the vise’s handle while I pulled on the bike frame, and after a moment we heard a crack. The seatpost definitely had moved within the frame. So we reversed grips, and I pushed on the frame while my colleague pulled on the vise. Another crack and more movement.
I sprayed more apple cider vinegar on the area where the seatpost joins the frame, and then things moved more easily. With the two of us twisting the frame first one way and then the other, applying upward pressure the entire time, the frame soon came off the seatpost completely.
With that done, the work can truly begin. I’ve ordered the paint (although there’s a lot of work to be done yet before that’s needed) and it will arrive tomorrow.