Seat post fused into seat tube.

[Shaun]

Apologies for the deleted posts, but as peanut has left the forums and deleted a few posts on his way out there seemed little point in having them cluttering up the thread.

So, is the post out then?

 

[mr Mag00]

thats what i wanted to know

 

[Rhythm Thief]

So, is the post out then?

Peanut's posts are, yes ...

... oh, I see what you mean.

 

[rich p]

I've hacksawed a carbon one that had seized in ali but it may be harder for an ali in steel. My one was a relatively easy job.

 

[Zippy]

<throws hat in first...>

Post still firmly stuck despite daily doses of caustic in the downtube.

I have the BB dismantled now and feeding the stuff down the tube upside down (the cycle that is, not me). I rest the sawn off seat tube on a flexible sanding block wrapped in polythene to seal off the post and plug the BB with a wadge of polythene once the caustic is up to the brim to stop the effervescent reaction from emptying the liquid back out.

I haven't got easy access to a bench vice, but have a good sized plumber's wrench and claw hammer to keep having daily whacks and wrenches at it - getting nowhere.

Luckily I am half an hour's walk from work so can keep up the active transport to work while this becomes a winter project.

The seat post is about 3mm thick though so I hope I don't have to wait for the NaOH to eat its way through - it could be March before I can ride again!

See the beast attached ...

 

[Panter]

Ah well, at least the weather should've improved by then

 

[Zippy]

Looking at all the options, if I go down the hacksaw route and I find bits of aluminium that will not prize off, I don't want to chisel bulges into the downtube.

I have seen hand reamers at the right diameter, but I need to ream down about 7 inches - do reamers come with drill shafts of that length either by hand or electric drill bits?

Later... Sod this, I'm getting the hacksaw blades out!

 

[stewie griffin]

I can't understand why caustic would work for me & not for you?

Can you see any difference at all when you inspect the post, does it look as though it's eating away the aluminium? Is the post wall any thinner?

Mine got very hot when I did it, does yours? Having said that, the paintwork didn't matter on mine so I plugged the BB hole & did it the right way up, it was simple to keep it totally submerged with the post cut off flush with the frame, renewing the mix now & again.

I would say keep at it, it will give in, it simply has to do, unless the laws of chemistry have been changed recently?

 

[Zippy]

Two hours later and I've cut grooves down the seat tube and the pieces are still oxide-welded to the downtube - the whole length. I had hoped to keep some seatpin outside the frame for pulling but they broke off when hammering a blunt screwdriver between seatpin and downtube, so its a case of chiselling the bits out.

I'm glad my dentist doesn't take the same approach! :?:

So in case I can't get the deepest bits out (could maybe drive them further down). - how much seat post should I have in the downtube to be safe?

See progress to date attached. Will soak the bits in ammonia tonight and see if that frees anything. Yes - I have cleaned out the sodium hydroxide first!

 

[Zippy]

I can't understand why caustic would work for me & not for you?

Can you see any difference at all when you inspect the post, does it look as though it's eating away the aluminium? Is the post wall any thinner?

Mine got very hot when I did it, does yours? Having said that, the paintwork didn't matter on mine so I plugged the BB hole & did it the right way up, it was simple to keep it totally submerged with the post cut off flush with the frame, renewing the mix now & again.

I would say keep at it, it will give in, it simply has to do, unless the laws of chemistry have been changed recently?

I can't understand this either unless the product I have is "cut" with some filler or something. The instructions for cleaning drains is 40g to 0.5 litre and I am using 80g, in fact this is a saturated solution as no more product will dissolve and sediments out.

I see no real difference after 4 days of the downtube being regularly filled with NaOH. However, when I empty the waste out there is only a trickle of black thick waste and not the 0.5 litre I put in the night before so something is happening. As the reaction takes place though the volume of NaOH goes down so the end of the seat tube is no longer submerged.

Yes, mine got very hot (didn't boil) and when I filled the tube the NaOH was frothing out which is why I plugged it to keep the solution inside.

I think now I have lost the advantage of any leverage I must either chisel the insides out or use more NaOH as you say and of course - I can pour the stuff straight down with the bike right way up tonight and just plug the top of the tube.

There's another consideration - my paint is not being lifted at all though some spills got onto my alloy rims and they were burned slightly. I wonder if the solution is just not strong enough.

I wonder if the seat stem is aluminium or some other Alu-alloy?

Stewie - did you completely burn your stem out or did it go to a point where you could lever the remainder?

 

[hubgearfreak]

how much seat post should I have in the downtube to be safe?

inserting just a few inches will be enough

i've got, or seen seat posts with a min. insertion mark that's surprisingly near the bottom. go to your LBS and look at the seat posts, you'll see minimum marks on some, and there's your answer

 

[stewie griffin]

I wonder if the solution is just not strong enough.

I wonder if the seat stem is aluminium or some other Alu-alloy?

Stewie - did you completely burn your stem out or did it go to a point where you could lever the remainder?

I guess it's got to be one or the other, weaker solution or a different alloy.

I was left with nothing except the very top that hadn't been submerged as much due to the solutions evaporating (boiling?) off.
It pulled out easily with pliers, a bit of a surprise at the time because it gave the appearance of the post still being intact, nothing below that, totally gone, I can't be exact on how long it took, it's a few years ago when I did it.

The bike was a Scott San Francisco hybrid I was given, it looked OK but I could see it had stood outside. A pretty low end bike so I imagine a cheap seat post. I wonder how much the "alloys" vary between different bikes?

 

[Zippy]

Worth a mention here I think if using caustic soda to melt out an aluminium seatpost from a steel frame.

I noticed when handling the frame today that the headset bearings sounded de-greased when the steering rotated.

This is because the downtube is open ended to the cross bar and the front bar leading to the headset, so when flicking the frame over to pour out the waste solution some of it has been finding its way to the headset and degreasing it.

I noticed this when I turned the bike the right way up tonight when pouring in the NaOH the right way up. Because the seat stem is now away from the crossbar I heard the solution making its way across the crossbar and into the headset. So beware, when the seatpost finally gives way, some lye may find its way along the crossbar to the headset.

I suppose the best precaution would be to hoist the front end of the frame up so the lye naturally returns to the downtube where it is needed and of course to make sure the stripped out BB is plugged.

Luckily for me everything up that end is steel and I just have to clean out and repack my bearings.

The packed downtube is soaking in NaOH tonight, hopefully to come out tomorrow - pics promised! Err - scratch that, I just discovered the bloomin NaOH has been leaking out of the rear wheel brackets (must be open brazed to the downtube) through the water drain holes - so now I know why the lye wasn't working!

 

[raindog]

Good grief, I'll be glad when this is all over and I can sleep properly again.

 

[Zippy]

Raindog - good news - you can sleep properly again!

One sacrificial 1/4" chisel, about 4 hours with a good hacksaw blade and a long screwdriver, and ...