The alu BB cups will be at the same cold temperature as the steel BB shell. Both will shrink, but alu shrinks more than steel. I did this with the tandem eccentric.
Could try heating the whole area. Constrained expansion might mean it’s enough to loosen the cups. Whether you can heat it enough to work without heating it so much you damage the paint is anyone’s guess.
Alu cups will.contract more
I had a 21 year old BB stuck in a old Raleigh that came out just from heating with a hair dryer. Was the kind of BB that's installed with a headset spanner too so no issues with purchase to begin with.
I would get a hole saw on one cup to get the cartridge out, big bolt to get the other cup out and hacksaw and chisel to get the remainder of the original cup out. Probably be the easiest with out damaging the paint
Hole saw is exactly the kind of evil genius tip I've been looking for.
Should I hole saw the DS or NDS cup? I think body and spindle of the BB are connected to the DS cup btw.
Does the nds cup come out. It should do with plus gas and effort. Of the cups disintergrate through corrosion it wontm and then just knock the bb through.
For the damaged cup i would get a 6 pin tool made up a bit like the royce or mavic bb tool and drill 6 holes in the cup and remove.
Its either that or drill the alloy cups to the point the bb can be hammered out. The remaining cup can be removed with caustic soda.
It will come out.
Heat can work too. Used thar before spent 5 hours once getting a bb out of a cheap alloy hybrid. I started so i will finish i kept telling myself.
+1 for the hole saw idea. As soon as you can knock the cartridge out you should be on easy street. My only concern is that aluminium oxide (alu+steel+water) could be the reason the cups are not moving, in which case they may put up a fight.
Drill out the nds cup to the largest size you can without cutting in to the frame, this should allow you to knock the cartridge out, they normally only sit in the drive side cup it’s not usually one piece.
This will then leave you with the two cups still in the frame.
Use a hacksaw to gently cut through the nds cup at around the point where the chain stay meets the BB shell, as that will have the least amount of threads that could be damaged.
When getting close to the threads, you should be able to chisel the cups inwards, break what remains of the threads and fold the cup in on itself. It should then come undone relatively easily.
On the DS cup you could do the same or do big bolt thing to get it out, since it’s a left handed thread.
I attempted this. It took two or three evenings and maybe four charge cycles of the Makita. And it killed like five drill bits. The spindle is now out, as is the NDS cartridge bearing, but most of the BB has stayed put.
I could maybe nibble away at the remains of the NDS cup some more, though I've already troubled the frame's BB shell threads in one small area. It might give me a chance to knock out some more BB parts (hammering from DS side). But without a spindle I would just be drifting that 2mm black surface showing behind the shredded alu teeth.
I'm quite tempted to just dissolve the whole lot out with caustic soda but I would then need to repaint (which is a shame as the paint is quite cool). Does anyone know of a way to protect paintwork in a caustic bath? Like can I coat the whole area in silicone bathroom sealant or maybe heavy grease / vaseline? Peanut butter?
looks like youre not far off getting that out. you just need to get more of the lip off the cup to let the cartridge come out.
now you can access it, I would try get a small flap wheel in your drill and grind the cup away. should make quite short work of it and it will not get hot and burn the paint. that would get the cartridge out and then you can cut the cups, fold them in and get it all out.
What about finding a way to seal the BB shell from the outside and pour the soda in through the seat post? Would save most of the paint, if you find a way to do it.
Flap wheel is a great shout. You're talking about attacking the NDS cup (or what's left of it) right? So I can push the cartridge out towards the NDS?
I can get these locally:
If I could plug up the irregular holes in the BB (i.e. the two cup faces) then that tactic would work until the caustic soda makes a hole through a cup and all the caustic soda would splurge out over the paint. And it wouldn't really be possible to seal again.
Yeah, get one of those on the remains and you’ll nearly have that thing out
Yep dunno why my edit didn’t go through. I’d suggested the possibility of dissolving the NDS first, resting the bike at a vertical angle to avoid flooding out of the drive side with the cup. The BB is down to the frame shell on that side, so if one could (mildly) melt some flat PVC onto the BB shell or find another way of sealing off just that side, that’s half the job done, probably a bit more.
Just tossing plausible ideas out there, I can see you’re not inclined to try the above.
Ah ok cool, you're talking about laying the frame on its side, NDS down? Yeah that sounds like it has a high chance of saving the paint. However, the caustic soda foams a lot when it's reacting, so it might blow out the DS anyway. It foamed like crazy in summer when I got a seatpost out of the tandem frame.
That’s useful to know, only done it once and didn’t notice or don’t remember that. Good thing you’re on it, it’s a nice paint job.
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