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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 05-22-05, 01:28 PM   #1
mcatano
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Ugh.

So I've been building up this beater track frame that a friend gave me a while ago and finally got around to spray bombing it last night. When I went to take it down, the twine that it was held up with slipped and the bike came crashing down onto the concrete floor of our basement. There is now a significant dent in the drive side threads on the bottom bracket shell. I'm hoping that this can maybe be heated and mashed back into shape, but I don't really have my hopes up. I would just take it to the LBS tomorrow, but it's a long weekend up here in Canada so it won't be open again until tuesday. I don't want to stew for that long, so somebody give me some hope, ok?

m.
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Old 05-22-05, 02:21 PM   #2
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...perhaps it can be formed back and rethreaded, but i wouldn't use heat when reforming, you could comprimise the strength of the material. which already has happened by denting it in the first place. how bad is the dent? got a picture?
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Old 05-22-05, 02:43 PM   #3
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Ouch. Yeah, I'm not to sure about that one. Travsi is probably right about the heat, you might be able to bang it out and then tap it, but im not sure.
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Old 05-22-05, 02:58 PM   #4
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Post a pic. Depending on the dent's location and size you might be able to just file it down or even cut out a small section of the BB shell (not great, but it depends on how much work you want to put into it).

If nothing else, you could probably drive a cone & rod through from the NDS to push the BB shell back out. Of course this will likely mangle your threads and they'll have to be chased if not re-cut. I have no idea where you'll get the rod. It all depends on how much it's worth to you.

Last edited by bostontrevor; 05-22-05 at 05:44 PM.
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Old 05-22-05, 05:21 PM   #5
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On a thread by herent it is pointed out that you do need threads. So, bash it back and get a threadless bb.
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Old 05-22-05, 05:38 PM   #6
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Quote:
Originally Posted by icithecat
On a thread by herent it is pointed out that you do need threads. So, bash it back and get a threadless bb.
What does a threadless bottom bracket look like?
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Old 05-22-05, 05:40 PM   #7
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Quote:
Originally Posted by icithecat
On a thread by herent it is pointed out that you do need threads. So, bash it back and get a threadless bb.
I'm going to stick my neck out here and disagree. I really do not like the idea of a threadless bb, it just doesnt make sense to me.
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Old 05-22-05, 05:44 PM   #8
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Um. Ok.
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Old 05-22-05, 06:17 PM   #9
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On the edge of tears
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Old 05-22-05, 06:24 PM   #10
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is the BB shell itself dented? or are the threads just mangled?
If it's just the threads you might just be able to get them chased and cleaned up. and if that does fail, you could go the Mavic/unthreaded BB route. Or have it reamed and threaded italian.

if the BB shell itself is mangled, then Idunno.
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Old 05-22-05, 06:31 PM   #11
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Quote:
Originally Posted by Jaminsky
I'm going to stick my neck out here and disagree. I really do not like the idea of a threadless bb, it just doesnt make sense to me.
Actually, I think they're a pretty cool idea. I have a Mavic that I'm holding onto as a 'problem-solver' for the future. There's not much torque on any BB body or cup (unless your bearings are siezed) so that shouldn't be a problem. The BB shell has to be refaced to something like 45 degrees and the adjusting/locking rings have a conical face to match.

Basically, they're self-centering, chainline tweakable and remove thread compatibility (french/italian/english) issues. If you do manage to mung up the threads you just replace the BB not the frame or shell. So, does anyone know why all bikes aren't designed to use this type BB? Is there a drawback to these that I'm unaware of?

Jim
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Old 05-22-05, 06:47 PM   #12
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It seems to me that it's one of those classic, "why didn't we think of that?" things.

Why are track cogs threaded on and not bolted on?

In fact, Ashtabula-style one-piece cranks have used this for years, after a fashion.
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Old 05-23-05, 12:30 PM   #13
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Quote:
Originally Posted by Jaminsky
I'm going to stick my neck out here and disagree. I really do not like the idea of a threadless bb, it just doesnt make sense to me.
So what's your solution, then?

If a threadless bottom bracket will make this poor bike rideable again, I'm all for it.
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Old 05-23-05, 01:23 PM   #14
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Quote:
Originally Posted by jimv
Actually, I think they're a pretty cool idea. I have a Mavic that I'm holding onto as a 'problem-solver' for the future. There's not much torque on any BB body or cup (unless your bearings are siezed) so that shouldn't be a problem. The BB shell has to be refaced to something like 45 degrees and the adjusting/locking rings have a conical face to match.

Basically, they're self-centering, chainline tweakable and remove thread compatibility (french/italian/english) issues. If you do manage to mung up the threads you just replace the BB not the frame or shell. So, does anyone know why all bikes aren't designed to use this type BB? Is there a drawback to these that I'm unaware of?

Jim
Do I read correctly that a threadless BB could be used in a french-threaded shell (on an old Peugeot, e.g.)?
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Old 05-23-05, 01:24 PM   #15
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Quote:
Originally Posted by bostontrevor
It seems to me that it's one of those classic, "why didn't we think of that?" things.

Why are track cogs threaded on and not bolted on?

In fact, Ashtabula-style one-piece cranks have used this for years, after a fashion.
Miche makes a nifty splined track cog system (though the adapter is threaded on first).
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Old 05-23-05, 01:29 PM   #16
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Quote:
Originally Posted by weed eater
Do I read correctly that a threadless BB could be used in a french-threaded shell (on an old Peugeot, e.g.)?
yup.
the BB shell first has to be machined a bit for it to work.
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Old 05-23-05, 01:31 PM   #17
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Quote:
Originally Posted by weed eater
Do I read correctly that a threadless BB could be used in a french-threaded shell (on an old Peugeot, e.g.)?
That's my understanding but I have to confess I have NO experience with French threaded BBs. The only issue I could see, would be if the BB shell was a significantly smaller diameter than say an english one. Then the Threadless BB body just might not fit. I hope someone with experience with this type of BB can clear this up for certain.

Jim

EDIT: Well there you have it....baxtefer got in a good answer for us.....Thanks
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Old 05-23-05, 01:32 PM   #18
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Miche makes a nifty splined track cog system (though the adapter is threaded on first).
Yes, and Level makes a hub with a bolt on cog.

I'm not asking why aren't those products on the market, because they are, I'm saying that the case of the threadless bottom bracket may just be one of those things that wasn't invented for a long time because a threaded BB was just how it was alway done.

It made sense when the BB shell housed loose bearings and a spindle, but now with BB units, it doesn't make sense anymore.
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Old 05-23-05, 04:02 PM   #19
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So here are some pictures of the dent. Looking at it now, it doesn't seem quite as bad as it did yesterday, but I guess I'll have to take it in tomorrow and see what the verdict is. Any suggestions on how I might be able to MacGuyver this back into shape myself are always appreciated.




Yoinks.

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Old 05-23-05, 04:02 PM   #20
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stronglight sells a threadless bb as well.
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Old 05-23-05, 04:12 PM   #21
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Quote:
Originally Posted by mcatano
So I've been building up this beater track frame that a friend gave me a while ago and finally got around to spray bombing it last night. When I went to take it down, the twine that it was held up with slipped and the bike came crashing down onto the concrete floor of our basement. There is now a significant dent in the drive side threads on the bottom bracket shell. I'm hoping that this can maybe be heated and mashed back into shape, but I don't really have my hopes up. I would just take it to the LBS tomorrow, but it's a long weekend up here in Canada so it won't be open again until tuesday. I don't want to stew for that long, so somebody give me some hope, ok?
Definitely have hope, man!

There is a bewildering array of ways to form threads in metal. I don't know exactly how the threads for a BB are chased, but for smaller diameters tools called taps are used. Most taps are cutting tools which cut a threads as they are twisted into a hole, but there are also special types of taps used for fixing damaged threads. What these generally do is they PUSH the metal threads back into place. I would expect that something similar exists for bottom brackets.

DON'T try and rig something up at home. Leave this one for the experts, or at least a mechanic with a big reference book that says exactly what to do in this situation...
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Old 05-23-05, 04:18 PM   #22
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Sorry to say, but dang that is worse than I thought you were describing. As to fixing, here is the only thing that pops into my head. Apiece of wooden dowling of a diameter that just fits int the non damaged side. cut off a two inch length. Slice lengthwise into two halves. Remove enough material from the flats that they fit in the damaged side with some slop. Insert something wedge shaped between the two halves. Hammer in gently, forcing the tubing round again. Good luck.
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Old 05-23-05, 09:21 PM   #23
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Good idea. I wonder if you could use a BB cup or something so that you don't end up just mashing up the wood. It looks pretty heinous.
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Old 05-23-05, 09:24 PM   #24
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Here's another suggestion: it's lugged steel, so replacing the bottom bracket shell is straightforward. Maybe you can find a local framebuilder to do it pretty cheap?

I'm suggesting this because I'm not sure I'd want to ride on that BB shell even if you can somehow get it back into shape. Bending the steel like that is almost certain to weaken it.
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Old 05-23-05, 09:34 PM   #25
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I would still try to mash it back into shape. I mean, just because the most common place for frame failure is the BB shell, I don't see why you should get all bent out of shape (ha, I kid!).

Seriously, though. I'd still try to bend it back. Steel has a wonderful failure mode, so if it fails at the BB shell, it'll just crack and you won't be able to ride it until you get the shell replaced. Or maybe it won't die at all. But it's not like it's the downtube and the bike's going to fold up on you ta speed.
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