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Cross threaded bottom bracket

Old 04-20-22, 12:03 AM
  #1  
gululok
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Cross threaded bottom bracket

I swapped out my old cup/cone bottom bracket to a sealed cartridge bottom bracket, and may have cross threaded the drive side. The top edge is bottomed out, but the bottom edge has a gap. Can I live with this, or do I need to get a new cartridge? The spindle just barely turns without the crank, but seems to turn well enough with the crank's leverage.

The thread on the cartridge is aluminum, whereas the thread on the frame is steel, so the steel thread should be undamaged, and able to accept a new cartridge, right?
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Old 04-20-22, 12:43 AM
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ridelikeaturtle
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I might pull it out and confirm you actually cross-threaded it. Could it be the case the face isn't so flat, and it just looks wonky but really isn't? I'd have thought you'd have known you were cross-threading it well before you bottomed it out against the frame.
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Old 04-20-22, 07:16 AM
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gululok
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Originally Posted by ridelikeaturtle View Post
I might pull it out and confirm you actually cross-threaded it. Could it be the case the face isn't so flat, and it just looks wonky but really isn't? I'd have thought you'd have known you were cross-threading it well before you bottomed it out against the frame.
I started threading it a few turns, felt resistance, backed it out, saw that it's crossthreaded. I then futzed around for an hour cleaning off metal filings, scraping the threads with a screwdriver hoping I can straighten the threads (I don't have an appropriate tap), couldn't get it in straight, and thought, "Maybe I imagined it. Bottom bracket is supposed to be tight, right? If it's crossthreaded I'd need a new cartridge anyway. Just crank it in and see how it looks.". Which got me here.

In comparison the other side threaded in smooth and without issue.
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Old 04-20-22, 07:38 AM
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Bald Paul
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Hopefully you'll be able to unthread the drive side. Sometimes when you force in a piece cross-threaded, it has a tendency to not want to come out.
If you do remove it, use a stiff bristled wire brush and some spray cleaner to thoroughly clean the threads of your BB. Inspect the threads, just in case. I suspect they'll be okay, as the aluminum will strip out before the steel will. Use a little grease when you install the new cartridge, and don't force it!
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Old 04-20-22, 09:41 AM
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I would take it to a shop and have the shell chased. This will realign the threads.
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Old 04-20-22, 10:17 AM
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Are you sure that the sealed cartridge unit is the proper size and thread pitch? If you were able to “back it out” you can check to verify proper thread pitch with the old drive side cup. See if the threads of the old cup seat perfectly in the threads of the cartridge bearing unit. As mentioned, the aluminum threads on the cartridge unit are the ones most likely damaged although there may be bits of aluminum left in the steel bottom bracket shell threading and definitely need to be cleaned out. IF the cartridge unit is, in fact, the right size, and the threads have been cross-threaded, it’s possible that your LBS may be able to “chase” the threads and save the day.
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Old 04-20-22, 11:31 AM
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Originally Posted by 2old View Post
I would take it to a shop and have the shell chased. This will realign the threads.
Can I do that with the end cap of the cup/cone BB I took out?
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Old 04-20-22, 11:38 AM
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Probably, but I think you said it's steel, so I doubt the threads were affected. Possibly just clean the aluminum from them.
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Old 04-20-22, 12:56 PM
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I guess the first question is if your original DS cup had a gap?

The next is whether you can thread the new NDS support cap in or is the cartridge off-center so it won’t fit over the cartridge?

John
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Old 04-20-22, 01:58 PM
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Originally Posted by 2old View Post
I would take it to a shop and have the shell chased. This will realign the threads.
Originally Posted by gululok View Post
Can I do that with the end cap of the cup/cone BB I took out?
...with the proper set of piloted taps, it's a simple job, and takes about ten minutes. So most places, it doesn't cost much to have it done. The piloted taps are very handy in a case like you describe, because unless you get the threads, on whatever you're using to chase it clean, going in there straight, you can actually make the problem worse.

AS has already been noted, the cup inserts for sealed units are either plastic or aluminum alloy. So it's pretty difficult to damage the BB threads, if your BB shell is steel. If your BB shell is aluminum, that's all the more reason to use a piloted tap to clean this up. Which is what I would do.
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Old 04-21-22, 08:01 AM
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You might consider installing the NDS (non drive side) cup first, just temporarily. This helps "pilot" the cartridge body as you thread it in from the DS (drive side). As you thread the cartridge in, go over to the NDS and look through the hole in the center of the cup and check your work to make sure that spindle is coming through dead center. This is a method I use pretty often, even as a preventative measure. Once that NDS end of the spindle enters the NDS cup, you usually have enough DS threads solidly engaged...and you can then remove the NDS cup and continue threading the cartridge body in from the DS.

I have "lightly" cross threaded BB catridges in the past (before using this method) and was able to rectify by using this "piloting" method.

Chasing the threads with the proper tools is ideal. But you may be able to save it at home on your own as well.
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