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Framebuilders Thinking about a custom frame? Lugged vs Fillet Brazed. Different Frame materials? Newvex or Pacenti Lugs? why get a custom Road, Mountain, or Track Frame? Got a question about framebuilding? Lets discuss framebuilding at it's finest.

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Old 07-01-09, 08:48 PM   #1
clasher 
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Swapping out BB shell

Hi, I have an nice motobecane frame, but the BB is french-threaded, and the drive-side is also seized on there. I've tried the bike-in-a-bench-vise trick, and thought briefly about welding a big nut on to get a better grip with a big-ass-wrench™ and a few other hairbrained schemes came to mind, but I've yet to try anything that might ruin the bike.

I'm thinking that it might just be easier to buy a new BB shell with standard threading and then I get a new sealed cartridge BB for 30 bucks or whatever and still end up coming out ahead instead of buying a Phil's.

I'm proficient with a torch, I worked for a while brazing lots of copper pipes with silver alloy, and got pretty good at it... but I'm a bit unsure about to go about removing and replacing a BB without having everything else get out of whack on the bike. I imagine some sort of jig is going to be involved, but I'm having a time picturing exactly how to do this.

I'd like to get more into framebuilding anyway, so if there's plans for building a jig or whatever, I don't mind doing that as I'd likely end up using it one day.

TIA, cheers!
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Old 07-01-09, 09:17 PM   #2
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Your just down the road. I'm in Pickering. I can see it as a chalenging project, but I don't see it as a reasonable alternative to just getting the old one out. I would immerse the BB in penetrating oil for a week, try heating the BB cooling the insert. Not really my area of expertise, take it to a good shop.

No mater how good your jig is the brazing skill will determine the result. It makes the task more difficult that you are starting with several tubes fixed, not sub-assemblies since that limits some of the dodges you might be able to pull. I would suggest not trying this approach if you actually want to fix the bike up.

Not familiar with the bike, is it lugged?
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Old 07-02-09, 04:45 PM   #3
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Yeah, it's an old lugged frame from the 70s. I guess I'll find a junker frame and see how the disassembly goes before I ruin this frame. I've always liked the ride of it...

Any good sources in Ontario for frame parts? Or should I just go online?
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Old 07-02-09, 07:36 PM   #4
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no point in replacing the bottom bracket. Just heating the cup is often enough to get it out. Velo Orange now has a sealed French bb if you can get it out, which I'm sure you can.
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Old 07-02-09, 08:51 PM   #5
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I've heard people mention that and I vaguely remember trying to heat the cup up, but I must not have got it hot enough. How hot do you get it? I assume nothing like cherry red, right? I'm using an oxy-acetylene torch so that wouldn't be hard to over-heat it.

Do you have a link to the velo orange BB? I only saw a raleigh threaded one on their site.
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Old 07-02-09, 10:13 PM   #6
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Quote:
Originally Posted by clasher View Post
Do you have a link to the velo orange BB? I only saw a raleigh threaded one on their site.
Here's the Velo-Orange French thread BB: http://www.velo-orange.com/grcrufrthbob.html

I'd try to avoid replacing the whole shell. I've done it, and it holds up well, but it's a big job, and puts a lot of heat on all those tubes down there. The bikes I've done it one had physical failure of the BB shell, not merely desire to change the threading.
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Old 07-03-09, 05:45 AM   #7
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Hey Clasher,
Many Motobecanes had SWISS threading. Perhaps you can give that a try...
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Old 07-03-09, 03:41 PM   #8
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Tuz... I'd have to get the drive-side cup out before I could figure out which threading it is for sure, I think. I just took the torch to it now and hopefully that can help me get it out and save me the trouble of swapping out the shell. The velo orange BB would be perfect and cheaper than replacing the shell.
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Old 07-03-09, 04:38 PM   #9
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Oh I just meant that you could try wrenching the cup clockwise before attempting a more aggressive method.
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Old 07-04-09, 02:40 PM   #10
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Oh yeah, turns out this has Swiss threading... so that velo orange BB isn't going to work, unfortunately. That'd have been way too easy.
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Old 07-05-09, 08:06 AM   #11
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Are the cups usable? If so, reuse them with new bearings and a spindle for whichever crank you decide to use.
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Old 07-07-09, 01:29 AM   #12
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"Oh yeah, turns out this has Swiss threading... so that velo orange BB isn't going to work, unfortunately. That'd have been way too easy."

He also mentions a fit all BBs BB he has coming. Maybe. See recent entries.
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