Seat post fused into seat tube.

[Zippy]

you mean seat posts. we're taling road or mountain bike?

on mtb, they can be up to 450 mm long!!! but more typically 350 mm - you may well have 10 inches inside the frame!

instead of whacking with D lock, try grabbing the saddle and twisting the post.

do not go for the hacksaw yet - I can't figure out what you plan to cut anyway.

soak using penetrating fluid - the proper stuff, not WD40 - then apply some heat -and try twisting again.

try the ammonia next.

Thanks 02GF74. I'm talking MTB seat post. as far as I know there is no way of gauging the end of the stem in the tube (eg with a piece of stiff wire for feel) without sawing off the saddle platform?

I was twisting as well as whacking which is why I was getting my mrs to to the levering on the other end with the line prop - what a picture! D lock bar because it is solid steel but plastic coated so I didnt damage the frame.

As a last resort I would be sawing down the inside length of the stem to wrap the stem and pull it.

I'll try a week of daily PlusGas and twisting before I go to more drastic lengths, but I have ammonia at my disposal.

 

[Amanda P]

I'm not sure how knowing how long the seatpost is will help at this stage. It's got to come out however long it is.

Don't saw anything off the top is my advice. If you do, there'll be less to grip for twisting purposes, plus any plusgas/ammonia/caustic you fill the seat tube with will run out through the hole you make.

Persist with the plusgas and twisting. If that doesn't work, switch to caustic and twisting. It worked for me - and that was a bastard of a seatpost.

 

[Amanda P]

I would try to get hold of a slide hammer and attach it to the seatpost. That will definitely get the seatpost out and with zero damage .

If you were brave you could give the seatpost a good sharp belt with a hammer to see if you can shift it the wrong way first.

Both worth a try. I got mine to shift downwards slightly when belted with a hammer - but it didn't come up any easier than it had before at that stage. Although this moved the seatpost the wrong way, it might have broken or damaged the collar of gunk that was making the whole thing stick. Percussive maintenance is always worth a try (but think what you're hitting before you swing the hammer...)

I also made a slide hammer out of some threaded rod and an old lump hammer head - no dice with that though.

I also tried a sort of giant corkscrew arrangement to jack the seatpost out. The jacking arrangement worked like a charm - but instead of winching out the seatpost, it just collapsed the "corkscrew" like crushing a can. I didn't have the materials to hand to make a stronger rig at the time.

I think the tricks that worked for me were caustic soda trickled in daily, plus the considerable torque I was able to generate by securing the seatpost head in a vice and twisting on the whole bike. Initially, I actually yanked away the whole corner of the bench, vice and all like this, and had to strengthen the bench considerably.

 

[hubgearfreak]

do not go for the hacksaw yet - I can't figure out what you plan to cut anyway.

brilliant. one day you say how long it should take, the next, you say you don't what the procedure is. priceless

 

[Zippy]

Found a guy with a bench mounted metalwork vice on Freecycle so we'll see what tomorrow brings when I have a go at the upside down twisty method. May need one or three trips back to my new found friend with PlusGas and/or ammonia treatments in between.

 

[Zippy]

Went over to said guy, clamped seat post in said vice so neither of us could tighten it further and pulled clockwise and anticlockwise but the aluminium post was just smoothing off in the vice jaws; kept rolling out instead of gripping.

Seat post is a write-off now anyway so I guess its time to cut it off flush and start with the hacksaw down the seat tube a couple of times.

Well I had nothing else to do this weekend...

 

[Norm]

A vice won't grip a tube very cleanly. If you have written off the seat tube anyway, drill a hole through it and stick a metal rod through the middle, then twist that.

IMO, there is too big a chance that sawing down the seat tube will write the frame off too.

 

[stewie griffin]

It's my experience that caustic soda doesn't really do much to dissolve aluminium

Believe me it does! And quickly too. Maybe you were using a weak solution?

Zippy, see post #13.

 

[Zippy]

Thanks Stewie. The seat post is compromised now anyway and not very pretty! I don't think the down tube opens into the BB as I filled the same with ammonia through the drink bottle lugs (bike facing vertical so down tube was horizontal) and it didnt take much to fill it.

How strong a solution were you using please, how many solution changes and how long did it take?

Nothing to lose as I have the caustic soda powder, safety gear and a weekend to spare.

Alternative is to cut the stem off flush and saw down the downtube. Why would this write off the frame Norm? I don't understand. Object is to cut two or three vertical slots in the seat post and crush it out of the down tube. Plenty on here about that one.

Vice: it may be that this method works with steel seat pins, whereas aluminium ones grind away in the vice so the jaws can't make a positive grip.

 

[Amanda P]

Believe me it does! And quickly too. Maybe you were using a weak solution?

Zippy, see post #13.

Maybe I was using a weak solution. It didn't dissolve the aluminium, but it did dissolve the oxide gunk that was making the seat tube stick, so it did the trick.

Zippy, I would advise soaking with caustic soda for a bit before going down the sawing route. Sawing will be fiddly, and there is a danger of sawing through the seatpost and into the frame unless you're very careful.

It's quite hard to saw a tube through evenly; you'll tend to cut deeper at the end of the tube you're working through, and at its other end, than in the middle. To crush the tube in place, you really need slots all the way along its length, and that's really hard to do.

(I had to remove a corroded kingpin from a Moulton frame last week. In the end I did this by sawing and crushing, but it was VERY fiddly and hard work. Caustic was not an option for this, as both parts were steel).

You may be able to see the caustic solution fizzing when you introduce it. I concluded that it was being neutralized by the reaction, so I drained it out and replaced it from time to time; each time there was more fizzing, suggesting I was right, and that replacing it was worthwhile.

 

[Zippy]

Thanks Uncle Phil. I'll try this as I have a nice bottle of caustic soda (powder) waiting for me tonight. The seat post is ravaged from the vice last night so I don't mind sawing the seat end off the post now to pour the nasty stuff in. I'll check with a torch, but I don't think the down tube opens into the BB. The BB is a cassette so should be enclosed?

What concentration did you use? Not sure what a saturated solution would be for caustic.

Its kinda scary but I'm actually rather excited . Yes, I have anti chemical gloves and eye protection and I'll have a bucket of rinse water on stand by for splashes.

 

[Norm]

Why would this write off the frame Norm? I don't understand.

Because of the strong possiblity of...

Sawing will be fiddly, and there is a danger of sawing through the seatpost and into the frame unless you're very careful.

Also...

Alternative is to cut the stem off flush ...

Why cut the seat tube flush? If you do that, you've have nothing to get purchase on, nothing to pull against and nothing to try and force aside if you do manage cutting the post without damaging the frame.

Again, IMO, I'd leave as much seat post as possible.

 

[Amanda P]

I would do as you did with the ammonia, and squirt the stuff in through the bottle bosses, with the bike frame upside down. That way it'll pool around the seat post, where you need it most, without needing gallons of the stuff. You won't need to worry about whether bottom bracket's coming to any harm either. Cassette or open bottom bracket, it probably won't do it any good to be immersed in strong caustic - some of them have rubber seals and plastic components.

I used a small syringe to squirt caustic where I wanted it. No needle required, just the syringe. The ones you get with printer cartridge refilling kits would be about right, or a vet will supply one (you may need to explain what for). A disposable Pasteur pipette would be perfect (if you have access to those sort of lab supplies).

I mixed the caustic according to the instructions on the bottle for cleaning drains. I don't know what concentration this gave. I just scaled down the quantities because I only needed a few mls, not litres of solution. Possibly if I'd mixed it stronger, it would have worked quicker.

It's not that dangerous, just needs mixing and handling with a little respect and caution. If you weren't ready for the solution getting hot, you might get a shock! You wouldn't want it in your eyes, and it can fizz quite vigorously.

 

[Amanda P]

Oh, yes, and Norm (who cross-posted) is right - if you saw the seat post off flush with the frame, you'll have nothing to grip to twist and pull it out.

Even if you give up on chemicals, don't saw it off flush, because even if you saw grooves down the seat post's inside, and partly crush it, you'll still need something sticking out at the top to grip, twist and pull on.

You might need to saw the top off to saw grooves inside, but don't cut it off flush!

 

[Norm]

...Norm (who cross-posted)

I wasn't that cross, just mildly concerned.