'94 explosif

[one-eyed_jim]

I thought when people talked about melting, they meant using ammonia/equivalent to melt the corrosion between an aluminium post and a steel frame, because the ammonia won't damage the steel.

I don't think it means using heat. As Sheldon Brown points out, aluminium expands more than steel with heat, so heating a steel seat tube just makes the post all the more firmly stuck.

Melting, in this context, means just that - raising the temperature of the post until it becomes liquid and flows out of the frame. Aluminium melts in the 600°C range. You can heat most steels to that temperature without doing them any harm at all. Brass brazing alloys, for comparison, have typical melting points around 900°C.

 

[ruger44]

I thought when people talked about melting, they meant using ammonia/equivalent to melt the corrosion between an aluminium post and a steel frame, because the ammonia won't damage the steel.

I don't think it means using heat. As Sheldon Brown points out, aluminium expands more than steel with heat, so heating a steel seat tube just makes the post all the more firmly stuck. On the contrary he recommends freezing the post with a CO2 cannister as aluminium also shrinks more than steel.

You mean dissolving the aluminium?
I think the Southpole will be dissolved before the stem moves enough, when you try that with ammonia-like produkts!
Maybe it can work with just corroded-in posts though.

Freezing MIGHT work, but probably not with one cannister of gas... If you have unlimited gas supply it could work.

I still give the hacksawblade the best chances.

 

[Anthony]

I still think it's a cheap black-painted steel post, in which case all talk of melting, heating and probably even hacksaw blades is out of the window.

The seller has now posted an answer to the effect that he was advised to pour oil into the seat tube from the bb shell, but he hasn't tried it. You'd need quite a lot of penetrating oil to more than fill the inside of the post, but I suppose it wouldn't do any harm.

Although it looks bad, as it's the type of post where the clamp is detachable, they haven't really got anything to get hold of without drilling a hole in it, so there's no guarantee that anybody has had a serious go at shifting the thing yet.

 

[greenstiles]

Hmm............think it's an alu post meself............sorry to disagree, i could be wrong but we used to sell alu clampless posts..............yes usually steel if it ain't got a clamp, but a lot of modern BMX have em now as well as cheap hybrids..............i worked in an alu foundry for a few years it just looks alu under the paint. just a feeling.......hope it goes to a good home anyway..............had a 94 Explosive.............great ride.....would like one again

 

[fredgassit]

I'm with greenstiles on the alu post front. 15 years as a bike mechanic gives me that feeling. I can't see that it has gone further town than the top of the top tube.

I have had occasion to melt an alloy post out before - there was a hobbyist framebuilder 300 yards from the shop he did it on a number of occasions for us, admittedly on less delicate tubing with no problem apart from the paint of course.

 

[ruger44]

I'm with greenstiles on the alu post front. 15 years as a bike mechanic gives me that feeling. I can't see that it has gone further town than the top of the top tube.

I have had occasion to melt an alloy post out before - there was a hobbyist framebuilder 300 yards from the shop he did it on a number of occasions for us, admittedly on less delicate tubing with no problem apart from the paint of course.

Ordinary 'gasspipe' frames could bare the heat a lot better, I think :roll:

EDM can be used, It can be used with great precision to remove broken taps in for instance crankcases and some modernly equiped gunsmiths use it to remove stuck bullets from (precious) gunbarrels.

 

[one-eyed_jim]

Ordinary 'gasspipe' frames could bare the heat a lot better, I think :roll:

There really shouldn't be any problem, as long as the heat is applied evenly. Delicate heat-treated tubes like Reynolds 753 are silver-brazed at temperatures around 600-700°C

Here's framebuilder Dave Moulton on the subject:

To melt out the aluminum you are going to destroy the paint and you really need someone who knows how to handle an oxy-acetylene torch. You need what is known as a rosebud tip that gives a very large flame that will heat a large area. The frame needs to be in a vise; upside down. Heat the whole seat tube and seat lug area with the torch moving constantly until the whole area is an even dark red hot. The aluminum will start to melt and drip out; tap the frame with a small hammer further along the seat tube where it is still cold to help shake out the melting aluminum. Do not allow the frame to get to an orange red heat or the brazing will melt.

 

[Anthony]

Nevertheless, I somehow doubt whether that is what Giles_Clarkson2orm has in mind and has paid £155 for.

What's wrong with machining it out as Greenstiles suggests?

 

[wadsy]

Nevertheless, I somehow doubt whether that is what Giles_Clarkson2orm has in mind and has paid £155 for.

What's wrong with machining it out as Greenstiles suggests?

I spoke to both Bob Jackson Cycles and Argos and both were confident that the removal wouldn't be a problem. £15-£30 depending what needed to be done.

I decided not to bid in the end as it was quite a way to collect and I'm thinking I'll look for a '97 so I can use V-brakes.

 

[one-eyed_jim]

Nevertheless, I somehow doubt whether that is what Giles_Clarkson2orm has in mind and has paid £155 for.

I guess that would depend how much experience he has with this kind of problem...

What's wrong with machining it out as Greenstiles suggests?

Nothing much - I was only addressing my points to the few people who said that the heat involved in melting an aluminium seatpost would damage the steel tubes, not criticising any of the alternative methods suggested. But the main disadvantage of attempting to drill out the post is that it can be hard to drill precisely, and the risk of damaging the seat tube exists:

http://www.circleacycles.com/chris/?m=200708

Melting the post out doesn't run that risk if the heat is properly controlled, but of course it does destroy the paint. Swings and roundabouts.