Singlespeed & Fixed Gear - Can this be fixed?

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.

...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?

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.

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.

On a thread by herent it is pointed out that you do need threads. So, bash it back and get a threadless bb.

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?

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.

Um. Ok.

http://www.bikeforums.net/showthread.php?t=108557

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.

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

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.

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.

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.)?

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).

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.

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

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.

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.

http://ckdu.dal.ca/~mcatano/dent1.jpg
http://ckdu.dal.ca/~mcatano/dent2.jpg

Yoinks.

m.

stronglight sells a threadless bb as well.

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...

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.

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.

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.

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.

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.
Once upon a time, I was riding my bike down a hill at 40 mph, and the downtube started to crack. Thinking quickly, I whipped out a delicious blueberry pie. It was tough to choose to sacrifice the pie, which I had loved for all my life. But recently I had become more of a peach cobbler kind of guy, so I blinked away the tears, and smeared the pie across the rapidly faltering downtube.

Needless to say, my frame is now fine. I've taught this trick to a few buddies who are into DH mountain biking, and they swear by it now.

Took the frame in today - Dave, the wrench, said that he didn't have high hopes but that said he'd take it home and see what he could do. Knowing Dave, this means he'll most likely be able to fix it; if he didn't think he could fix it, he wouldn't have taken it. He's a little gruff like that. So it seems like worst case he'll put a threadless BB into it, best case he'll tap it out and chase the threads. Either way, I think it'll be OK. We'll see in a day or two for sure.

m.

Took the frame in today - Dave, the wrench, said that he didn't have high hopes but that said he'd take it home and see what he could do. Knowing Dave, this means he'll most likely be able to fix it; if he didn't think he could fix it, he wouldn't have taken it. He's a little gruff like that. So it seems like worst case he'll put a threadless BB into it, best case he'll tap it out and chase the threads. Either way, I think it'll be OK. We'll see in a day or two for sure.

m.

Hmmm. I just had a thought. Back when I was a young lad I was an auto mechanic (funny because I hate cars now and don't even own one). We had a device for spreading the end of an exhaust pipe just enough so that another pipe could fit inside. Sure, we used alot of heat to 'stretch' the pipe to a larger size but we also used to drop pipes and dent the ends and would use the same tool to re-round it.....no heat and very little effort was required for that fix. The spreading tool is very robust. So if your mechanic can't fix it, you could try bringing it to a muffler shop and throw a few $$ their way.

Jim

This is for sale on Craigslist Vancouver. Hopefully you will be in better shape.

The frame is very rusty! (but I like to think rust is a theft deterrant)
The frame has a hairline crack by the bottom bracket. The BB is locktite'd in place, and I cannot possibly predict how long it'll stay put. Depending on your weight, and how many curbs you jump, tt might last you a month, or it might last many more years.

Woke up this morning, found $5 on the ground outside my house and rode to the LBS to find my frame fixed, with a round BB shell and threads that work. Someone must've shoved a horseshoe up my bum last night while I was asleep.

m.

Woke up this morning, found $5 on the ground outside my house and rode to the LBS to find my frame fixed, with a round BB shell and threads that work. Someone must've shoved a horseshoe up my bum last night while I was asleep.

m.
Excellent! Did he say how he fixed it??

Jim

I think he used a variation on icithecat's suggestion of tapping it out with a plug and a wedge. He had to chase the threads afterwards, but apparently they weren't too bad and the BB went in fine.

He also said that having had this exact situation (things being dropped while they're drying) happen to him is why he always puts a pair of junk bb cups into frames when he's painting them... seems like a sensible idea.

m.