Freeing a seatpost that had been stuck for thirty years
The seatpost would not move. Not a millimeter, not with the saddle used as a lever, not with a rubber mallet, not after a week of penetrating oil dribbled down the gap between post and seat tube every evening. An aluminum post in a steel frame, left in a damp shed for what I now think was about thirty years, had corroded itself into place. This note is the sequence of what I tried and what finally worked, in order.
Week one: penetrating oil from the top, frame upside down so it could run down into the joint. No movement. Week two: the frame right way up, the bottom bracket removed, and a mixture of ammonia solution and water poured up into the seat tube from below, because aluminum oxide dissolves slowly in alkaline solution. I plugged the bottom with a cork and left it for five days, topping up as it crept out past the cork. Still no movement with the saddle as a lever, but there was a faint gritty sound when I tried, which there had not been before.
Week three was heat and cold. A heat gun on the seat tube for three minutes, until a drop of water hissed off it, then a bag of ice on the exposed post. The theory is that the steel expands and the aluminum contracts and the grip loosens. It moved. About two degrees of rotation, with the saddle clamped in the bench vise and the whole frame turned as the lever. Then it stopped again.
What finished it was repetition rather than force. Twice a day for four more days: heat, ice, twist two degrees one way, twist two degrees back, more ammonia down the gap. Each cycle gained a little. On the ninth day the post turned a full quarter turn and then, with a groan I could feel through the bench, came up 5 mm. From there it was another hour of working it up and down, cleaning the gray-white paste off each time, until it slid out in one piece.
The post itself is scrap; it is scored its whole length and bent 3 mm. The inside of the seat tube, honed gently with emery cloth wrapped around a dowel, is clean steel again. The new post gets a coat of grease and a date written in the notebook to pull it and re-grease once a year. That is the whole lesson, really.