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Old 12-11-06, 03:01 PM   #1
dirtyphotons
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how many bb rethreads?

can i get away with?

i've got an old motobecane that is an entirely unspectacular frame, but it was my first fixed gear and holds some sentimental value. i know the bottom bracket has been rethreaded at least once, and it's held up quite well, but i've stripped a few plastic caps in it and now the threads are starting to look damaged (cups still thread in smoothly, but it looks like some of the threads are chipping off).

my question is can you rethread an already rethreaded bb shell? will it work as well as the first rethread? will it not last as long?

this frame's been good to me, but i don't want to throw a lot more time and money into it if it's not worth the effort.
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Old 12-11-06, 03:03 PM   #2
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Plastic cups are very easy to strip. That's how they work.
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Old 12-11-06, 03:08 PM   #3
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Quote:
Originally Posted by operator
Plastic cups are very easy to strip. That's how they work.
yes they are. sorry, i should've been clearer. after several bottom bracket changes, some of which involved stripping plastic cups, some involved overtorqued alloy cups, the threads inside the frame's bb shell appear to be chipping off.

from what i understand about bb rethreads (pour metal into the shell on top of the existing threads, retap) it makes sense that these new threads would be less durable, but i really don't know if rethreading can be done over and over.
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Old 12-11-06, 03:22 PM   #4
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You really can't "re-thread" anything. You can chase the original threads to clean them up, but if they're going away you have only one option - ream out the tube, re-cut at a larger thread size, and set Heli-coil®. But I seriously doubt that a hanger tube would survive that trauma. If the threads really are going away, a new hanger tube is the better option.
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Old 12-11-06, 07:06 PM   #5
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thanks dmf!
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Old 12-11-06, 08:15 PM   #6
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have you tried chasing the threads? steel is a harder material than either plastic or aluminum, and seems unlikely that the bb threads would be compromise by the sort of intallation you're talking about. if the threads were damaged by overtorquing (however you're defining that), the crest of the threads would be flatten out or simply not there. the only time i've seen that is when a bb is cross threaded or the cups were seriously seized in the bb.

if chasing doesn't work, you might be able to tap the shell to italian.
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Old 12-11-06, 08:36 PM   #7
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thanks dafydd. by overtorquing i mean practically standing on a wrench. this was the first bike i ever built from a frame, and has gone through many different configurations and abuses.

seems like my understanding of what was originally done is probably amiss. i'll take it back to the bike shop that did the first "rethread."

Last edited by dirtyphotons; 12-12-06 at 08:41 AM.
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Old 12-11-06, 08:45 PM   #8
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Quote:
Originally Posted by dirtyphotons
thanks dfaydd. by overtorquing i mean practically standing on a wrench. this was the first bike i ever built from a frame, and has gone through many different configurations and abuses.

seems like my understanding of what was originally done is probably amiss. i'll take it back to the bike shop that did the first "rethread."
i guess what overtorquing means to me, it IS standing on the end of a 4' breaker bar trying to remove seized cups. and that's when the BB threads come out with the cups. moral of the story: you can never grease them too much.
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Old 12-12-06, 01:08 AM   #9
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If BB threads are no good and you want to keep riding, would this work for you: YST Universal Sealed Cartridge Bottom Brackets http://www.sheldonbrown.com/harris/b...ckets.html#yst ? "These YST bottom brackets fit any threaded 68-70 mm shell, and do not use the existing threads."
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Old 12-12-06, 02:32 AM   #10
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Quote:
Originally Posted by heyjaffy
If BB threads are no good and you want to keep riding, would this work for you: YST Universal Sealed Cartridge Bottom Brackets http://www.sheldonbrown.com/harris/b...ckets.html#yst ? "These YST bottom brackets fit any threaded 68-70 mm shell, and do not use the existing threads."
Just discussed this, less than half a page down.

Bottom Bracket conversion to cartridge
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Old 12-12-06, 08:41 AM   #11
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thanks for everyone's help! if the threads are badly damaged i'll look into the threadless.
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