Stuck seatpost Blues redux

[nirakaro]

OK, since I pulled the old Cannondale ST600, untouched for a fair few years, out of the cellar for a refurb, I've got two bikes with seized seatposts, one ali in a steel frame, t'other ali in an ali frame. They've both got the saddle at the right height at present, so I'm only interested in chemical, non-destructive methods for freeing them.
After a bit of background reading, I've armed myself with Plusgas, household ammonia, and 75% phosphoric acid, and I'm wondering what order to try those in. Any views?

[AndyA]

A good way to grip a stuck seatpost is with a set of aluminium tube blocks. I made some and they work well for medium stuck seatposts, sometimes I add some emery cloth between post and block for extra grip. If the post is really stuck they won't help, and its definitely possible to damage a frame like this

[Brucey]

caustic materials will attack an aluminium frame as well as an aluminium seat pin. So the approach for the cannondale shouldn't be the same as for the steel frame.

cheers

[hamster]

Remove the bottom bracket, invert the frame and then Plusgas down the inside of the seat tube. Repeat every few days and don't even think about trying to shift it until it's pickled for a week.

Pouring boiling water over the seat tube might do no harm as it may just crack the corrosion bond in the meantime, allowing the PlusGas to work down further.

i've inherited frames which have resisted (so much that the whole top of the seatpost was mangled) which have freed up almost immediately after a good dose of Plus Gas.

[nirakaro]

I'm treading warily around the old rule of, if it ain't broke, don't fix it: both these seatposts are currently doing their job – holding the saddle in the right place – just fine. So my main purpose, apart from the satisfaction of knowing everything underneath me is as it should be, is to make sure things aren't getting any worse. PlusGas seems to be the option least likely to do any damage (though also perhaps the least chemically active, so least likely to succeed), so I guess I'll go with that one first.

[Ugly]

My fixed bike, my go to this time of year, has a stuck seat pin and its been like it for 10 years or so, no problem. The frame has been recoated with the pin masked, the shot blasting gave in a rather nice matt finish.

[rualexander]

RJ The Bike Guy on youtube has several videos on the various methods of removing stuck seatposts.
https://www.youtube.com/playlist?list=P ... boqFl5Dvay