Ammonia dissolves Aluminium Oxide - does it?

[fausto99]

1. What did you do once you'd got the seatpost out? Did you rinse out the seat tube or anything like that? I'm just concerned about leaving caustic chemicals in there, as this isn't like a seat post, so I might end up with some "trapped" ammonia.

2. Is the ammonia you used just the ordinary household stuff you can get from the local Homebase.?

It's been a long time since I did it but yes, lots of water to rinse well afterwards and the ammonia was either from the local builder's merchant
or village hardware store.

[Northern_Monkey]

Personally wouldn’t put it on the aluminium frame, it will eat off the anodising/clear coat as a minimum. The hinge is safety critical so it doesn’t sound reasonable to use harsh chemicals on it.

Stuck seatposts are always the sacrificial part, people do stuff like cut them from the inside with a hacksaw blade to get the soliton to reach more of it then pull out in sections.

Is there no way you could disassemble it and look to ream the hole or smooth off the pin?

You can get freeze spray with penetrating lubricant, I’ve had good results with splitting corroded dissimilar metals with it.

[biketips666]

Personally wouldn’t put it on the aluminium frame, it will eat off the anodising/clear coat as a minimum. The hinge is safety critical so it doesn’t sound reasonable to use harsh chemicals on it.

You might be right.

Stuck seatposts are always the sacrificial part, people do stuff like cut them from the inside with a hacksaw blade to get the soliton to reach more of it then pull out in sections.

Yes, and the aluminium here isn't sacrificial, I need to keep it.

Is there no way you could disassemble it and look to ream the hole or smooth off the pin?

Nope, no way Jose. I spoke to a chap at C H White, who specialise in folders, including Dahons. He knows the bike I've got and agreed that there's no way to disassemble it.

Or to be ultra precise. If I ever get it loose enough to remove it, it will be loose enough to fold easily, in which case there's no point. There is a very short section of threaded hole in the end of the pin. I think it's some sort of M5, but when I tried to screw a bolt into it started to bind, so I think it might be a different thread, perhaps 0.6 instead of the usual 0.8. Nevertheless, I am fairly certain that if I could find a bolt that would go in it, given how short the threaded section is, and how tight the hinge pin is, and how insubstantial an M5 bolt is, it would simply break the bolt, as well as having to rig up some sort of level thing to get traction against.

You can get freeze spray with penetrating lubricant, I’ve had good results with splitting corroded dissimilar metals with it.

Just to reiterate, I don't need to split the two metals. The hinge isn't stuck like a stuck seat post. It's just very stiff.

As I did manage to free it up a bit over time, I think my way forward, for now, will be to disassemble the bike to get the frame in a position where it's easy to fold. And then just keep folding/unfolding repeatedly, while feeding it lube. If I apply heat, that should open up the joint, as it's a steel pin inside an aluminium knuckle, and aluminium expands more than steel. With any luck that might make the joint big enough to "flush" with whatever the lubricant I can get in there.

Cheers.

[Northern_Monkey]

Shame there is no way to punch it out.

Shock freeze lubricant was more to try and release any surface corrosion and than have it essentially ground up between the two surfaces as you flush out the joint. Or at least that was the rational in my head but maybe not reality!

My wife had a Dahon Espresso years back, I had to do the same eventually. Strip the frame and then spend 20 minutes opening and closing repeatedly. Did work eventually mind.

[MikeF]

If you're using ammonia it would be wise to use eye protection eg goggles, as IIRC the gas easily penetrates eyes