I have read somewhere, that ammonia will free corroded aluminum parts. It was recommended to free a stem from a fork.
That technique is mentioned on this page -- search on "ammonia" -- thew second time you find it leads to more info.
http://velonews.competitor.com/
Drano (caustic soda, sodium hydroxide, lye) removes anodizing from aluminum -- perhaps also corrosion, I don't know what it would do in an environment with steel and brass. I've succeeded in making a black rim into plain aluminum one with Drano.
Caustic soda dissolves in water and so you might have to wash out the penetrating oil, if the lye doesn't dissolve it.
Heating the BB shell will get the penetrating oil out and also may loosen the cups if you can keep them from taking on too much heat -- as aluminum has a greater coefficient of expansion than steel.
One thing the Velo News page recommended was to discharge a CO2 cartridge at the aluminum part to chill it, while also heating the surrounding steel part. That's hard with a BB cup though, with the axle inserted. Maybe you could pour cold water down the seat tube after heating the BB shell. That would at least make for an exciting moment or two. (and might also damage the frame if it had been heated enough. Don't get it red hot.). And, there are cartridge bearings inside the cups, so the water wouldn't reach the inner faces of the cups.
Or make bigger holes in the faces of the cups, so you can use a punch or improvised pin spanner with larger pins. Bad design in the first place, sorry to say, and if you rebuild, you will probably have the same problem again. Phil Wood and Shimano mounting rings/cups install and remove with a spline tool, no wonder. I've had a pair of non-stainless steel Phil Wood steel mounting rings that were hard to remove, but not impossible.
At 02:32 PM 7/18/2010, Simon Bird wrote:
>Message: 5
>Date: Sun, 18 Jul 2010 05:31:47 -0700 (PDT)
>From: simon bird <simonandonandon@yahoo.com>
>Subject: Re: [CR] Seized cup solved -the ultimate remover!
>To: classicrendezvous@bikelist.org
>Message-ID: <492138.8830.qm@web57512.mail.re1.yahoo.com>
>Content-Type: text/plain; charset=us-ascii
>
>This is a very timely topic for me, as I am trying to remove a Royce
>bottom bracket (alloy cups) from a Roberts road path frame at the moment.
>I can get no movement on either cup (lockrings are off at least)
>BOTH cups are of the pin spanner variety and my spring type green
>Park pin spanner is anyway not up to the job -I don't think. Also
>these are pretty classy BBs and ideally I'd like to save it, they
>have pressed in cartridge bearings I believe so should be very serviceable.
>As I cant remove the 'adjustable cup' (not actually how Royce BBs
>work being more like Phil or Mavic) I can't remove the axle to block
>up the holes so penetrating oil poured down the seat tube is finding
>the path of least resistance which is not via the seized threads. I
>think I'm going to have to make some kind of bath and soak the whole
>lower part of the frame.
>The frame will need to be repainted anyway so I was also considering
>heating the BB shell with a blow torch, Is the best thing to do lots
>of heating/cooling cycles and is it best to heat the shell or the
>cups -bearing in mind the cups are alloy?
>
>I will try the tranny fluid/thinners mix and look forward to any
>further advice.
>Simon Bird
>London England.
John S. Allen
7 University Park
Waltham, MA 02453-1523 USA
781 891-9307
jsallen@bikexprt.com
http://bikexprt.com