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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 05-04-06, 09:59 PM   #1
64deville
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Stripped Bottom Bracket - Where do I go from Here?

I'm truely between a rock and a hard place on this one. I have a 2000 or so Specialized FSR with a stripped BB Shell. Its not fully stripped, its just partially stripped on the drive side. About the 1st 5 threads in are worn down so the threads on the BB shell don't engage. There are about 5 good threads after the bad ones that still fully engage the BB Cartridge so it does tighten up OK. The problem is that the frame pretty much requires an E-Type front der (the kind that clamp between the BB and frame). When I put that in the mix I only have about 2 threads that I can really tighten against inside the BB shell. I just don't think thats enough.

I have looked into the threadless BB's made by YST and running a clamp on front der (instead of the E type). I've heard the threadless BB's are like putting a band-aid on a broken arm and can come loose under hard pedaling and creak a lot. Next up the clamp on front der rides at a very funny angle when I try and clamp it to the "seat tube". The front of the cage is 1-2 mm from the big ring but the rear of the cage is like 7-9mm from the big ring.

Next I looked into reaming the threads in the BB shell and tapping it for Italian Thread. This has some potential but I cant find a BB unit with a long enough spindle. Most Italian thread BB's are designed for road bike doubles and the longest spindle I can find for a 68mm BB shell is 109mm. I need at least 113mm to clear all the rings. I can find them for 70 mm shells all day long but none long enough for 68 mm shells.

The easy way out is to turn the bike into a single speed or one with 9spds in back and one up front.

Suggestions Please
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Old 05-04-06, 10:03 PM   #2
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P.S. - Anyone who solves this problem of mine gets a prize from my pile of parts.
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Old 05-05-06, 12:23 AM   #3
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Just checking: you aren't sticking a 2chainring clamp-on front derailleur on with a triple crankset are you? That would give you chain rub problems as though it were at the wrong angle.

Here's an idea that's not elegant at all, but it could be used to change the angle of a clamp-on front derailleur-- if you want to tilt the derailleur rearward, you drill a hole from the rear of the seat tube through toward the front of the seat tube. then drill through from the front. The holes should be such that you can run a bolt through them and then the piece of bolt at the forward hole supports the derailleur from below while the piece of bolt (or nut) at the rearward hole pushes down on the derailleur clamp. Then you use some tire tube as a boot so that the derailleur clamp is more secure.

By the way, be sure to use washers with your bolt/nut combination. And drill holes in a bike frame at your own risk-- not like I have analyzed the structural integrity of the thing.
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Old 05-05-06, 12:36 AM   #4
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Uh, drilling through the frame..?
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Old 05-05-06, 12:39 AM   #5
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Why not switch it over to Italian and run one of the shimano cartridge ones? They come in 107, 110, 113, 115, 118, and 122 mm. Cartridge bottom brackets don't really care if they're in a 70 or 68 mm shell, though I suppose you're going to end up with a spindle that's effectively 1mm shorter on the drive side and a whole 2mm of left side Q. Pick up a 1mm bb spacer if that's a problem

Also, you should be able to run any spindle you want in a cup and cone italian BB. Just get the cups and you're set.

All of this kind of ignores the E type FD issue, I'm assuming you already know how to work around that.

(Edited for clearer thoughts)

Last edited by Landgolier; 05-05-06 at 12:51 AM.
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Old 05-05-06, 06:23 AM   #6
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The frame is such on this frame that the tube the front der clamps to bends toward the front of the bike. This is what causes the goofy angle on the front der.

The thought of an Italian Thread BB set up for a 70mm spindle with a spacer or two crossed my mind but I've never run a 70mm BB in a 68mm Shell. The spindle lengths for the 70mm units are about the length I need. Will there be any other issues aside from installing a BB spacer or two?
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Old 05-05-06, 06:30 AM   #7
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I suppose JB Weld isn't an acceptable solution? You would get one last rebuild using the "correct" bottom bracket.

I've also heard the Mavic and YST threadless bb's are quick fixes and not for "hard-core" use so you probably are justified in avoiding them.

I concur that retapping to Italian and using a spacer if needed is the most attractive solution to your dilemma.
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Old 05-05-06, 10:22 AM   #8
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I would say you don't even need a spacer, assuming you run this FD, as it ought to be a pretty big spacer by itself.

Now here's what I don't know, and what you will have to ask Sheldon or some other sage about. Normally a shimano BB has the works screwing into the right side, and the other cup, which doesn't do much but provide a little support (they're often plastic) in the left. However, since an italian BB has the right side threaded backwards (right hand, but this is backwards because it unscrews itself), it would seem to me that it would be preferable to install the works on the left, where it's threaded correctly, and have the other cup on the right. The question is whether correct thread direction on the part that gets actual torque on it is more of an advantage than having the solid side of the BB on the drive side. I'd be curious which way the thing is actually marked -- I actually just bought an old italian bike and have been wondering about this.

Of course, if you run that FD you're talking about you're going to have to put the works in the right side, as the other cup won't clamp it down. Even if it's meant to go the other way, the threading is the same, so you'll be fine.
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Old 05-05-06, 11:51 AM   #9
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You can try to reconstruct the threads using something like jb weld. Put a thin coat of JB weld in the frame, over where the stripped threads are. Spray the BB lightly with PAM or some non-stick coating, and thread it into the existing good threads (just thread it in enough to hold, don't make it too tight, you want to get it out easy).

Wait for the JB weld to harden.

Unscrew the BB carefully, hopefully the non-stick spray will cause the JB weld not to adhere to it, so the result should be freshly cast JB weld threads. I'd wait a little while to let the JB weld fully harden before attempting to install the BB for real.

I repaired the threads on a plastic gear with JB weld (as in, it turned against another gear all the time), it held for like 5 years or something... quite a long time.

If you're willing to do "one last rebuild" as the guy said above, just go ahead and screw it in there without cooking spray. It'll never come out, that's for sure.
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Old 05-05-06, 01:01 PM   #10
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I don't know the dangers of heating the BB shell up to approximately 800 degrees F, but maybe you could use Dura Fix aluminum brazing rods to add some material to the BB shell and have it retapped for English threads.
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Old 05-05-06, 02:57 PM   #11
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800 degrees is OK.
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Old 05-05-06, 05:29 PM   #12
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Quote:
Originally Posted by spunkyruss
I don't know the dangers of heating the BB shell up to approximately 800 degrees F, but maybe you could use Dura Fix aluminum brazing rods to add some material to the BB shell and have it retapped for English threads.
Heating the frame will anneal (soften) the aluminum and take the
Heat Treatment out of that area.
I don't know what BB you are using, but I would see if the threads
could be chased or retapped by a mechanic/machine shop first.
If not I would ream and retap Italian on that one side and buy an
Italian E-type cup and use a BB spacer if needed.

Last edited by Soil_Sampler; 05-05-06 at 05:34 PM.
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Old 05-05-06, 06:20 PM   #13
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retap to italian threads and then get a phil wood (they have seperate cups so you could match those with a longer spindle).
check it out
http://sheldonbrown.com/harris/bottombrackets.html#phil
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Old 05-05-06, 06:52 PM   #14
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I've had to heat up a Chromo frame to unstick a seatpost before and I personally don't think Aluminum will hold up to 800 degrees but that is a very creative thought. The JB suggestion about creating some more material to retap is interesting too. I hadn't considered either.

I think I'm going to try the retapping method. If nothing else it will be an experience. I think I will practice on this old broken Cannondale frame I have laying around and see what happens.

Tools and stuff I know I will need:

REEMER to take care of the existing threads
BB - Likely a 70mm shell Shimano unit with a 115mm spindle
0-2 BB shell spacers

I have access to an Italian Tap

I thought I would use some Park Cutting fluid to help the process along a little.

Anything I'm missing?
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Old 05-05-06, 07:26 PM   #15
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Add elbow grease and patience and bake at 350 for 45 minutes. I'd get a toothbrush, or even better a toothbrush-sized wire brush for cleaning things out as you cut. Maybe a big bottle of rubbing alcohol or something like that to really flush it out and clean out all the cutting fluid. No sense making nice new threads and then galling them.

And let me know which way that shimano italian BB says it's supposed to be installed, I'm very interested.
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Old 05-05-06, 09:21 PM   #16
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Quote:
Originally Posted by Soil_Sampler
Heating the frame will anneal (soften) the aluminum and take the
Heat Treatment out of that area.
Not at 800 degrees it won't.
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Old 07-15-08, 07:44 AM   #17
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Quote:
Originally Posted by Eggplant Jeff View Post
You can try to reconstruct the threads using something like jb weld. Put a thin coat of JB weld in the frame, over where the stripped threads are. Spray the BB lightly with PAM or some non-stick coating, and thread it into the existing good threads (just thread it in enough to hold, don't make it too tight, you want to get it out easy).

Wait for the JB weld to harden.

Unscrew the BB carefully, hopefully the non-stick spray will cause the JB weld not to adhere to it, so the result should be freshly cast JB weld threads. I'd wait a little while to let the JB weld fully harden before attempting to install the BB for real.

I repaired the threads on a plastic gear with JB weld (as in, it turned against another gear all the time), it held for like 5 years or something... quite a long time.

If you're willing to do "one last rebuild" as the guy said above, just go ahead and screw it in there without cooking spray. It'll never come out, that's for sure.
i have the same problem on an old stingray style 20" polish Tyler brand bike. i thought of using jb weld and probably will so i'll let you all know how it goes. i didn't think of using the cooking spray, thats a good idea.
it doesn't need to be bulletproof for me its just for fun rides around the 'hood
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