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Old 09-16-12, 03:43 PM   #1
jpsawyer
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Stripped Bottom Bracket Cup

So i messed up. I got a Swiss threaded bottom bracket, but stripped the first two threads on one of the cups and now I cannot get it to go in straight. Am I stuck or can i do something to repair the cup and make it usable again? Thank you very much!
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Old 09-16-12, 04:50 PM   #2
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The non-drive side is the same as French thread (35.0 x 1.0mm); an established bike shop may have a tap they can use to chase the threads. The drive side is also 35.0 x 1.0 thread, but reverse thread (clockwise to loosen). These are considerably rarer taps for bike shops to have, but you may luck out.

FWIW, I have Swiss taps here, but I'm nowhere near Rhode Island.
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Old 09-16-12, 05:59 PM   #3
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if its the cup and not the frame just use a thread file to clean it up. 10 bucks for a file or a trip to a shop
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Old 09-16-12, 06:43 PM   #4
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if its the cup and not the frame just use a thread file to clean it up. 10 bucks for a file or a trip to a shop
do you know what the pitch is by chance on swiss threaded bottom brackets? Is it 1? I really do not know much about this stuff. This looks like the best option though and the simplest. Thanks
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Old 09-16-12, 07:56 PM   #5
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Use a small 3 corner file its really close to the angle of the thread. Hold the file straight and only file forward around the diameter of the BB cup
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Old 09-16-12, 08:59 PM   #6
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I don't mean to add insult to injury, but having done the same thing I make it a rule to always thread bottom bracket cups by hand (at least the first 1/2"); it will save you the grief you are going through.


A for your problem, did you strip the threads on the cup or inside the BB shell?
If you are replacing an old bottom bracket, and the damaged threads are in the shell, you may be able to chase the threads with the old cup.

Last edited by onespeedbiker; 09-16-12 at 09:03 PM.
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Old 09-17-12, 01:08 PM   #7
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do you know what the pitch is by chance on swiss threaded bottom brackets? Is it 1? I really do not know much about this stuff. This looks like the best option though and the simplest. Thanks
As above, Swiss thread is 35.0mm x 1.0mm, with reverse thread on the drive side (fixed cup).
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Old 09-17-12, 04:08 PM   #8
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I have been able to "start" many a cross-threaded bb cup by firstly threading in by hand to where it binds up, then observing the tilt of the face of the cup relative to the end of the bb shell.

With the tilt angle identified, I use a 3lb hammer and gently tap the face of the cup level, before putting a bit of rotation to it, this time using a wrench.

Using small increments of tapping and turning, the cup can usually be started in the damaged threads of the bb shell, keeping an ever-vigilant eye on any tilting of the cup in the bb shell.


If the cup threads are flattened, they should first be relieved, where needed, with the corner edge of a fine bastard or mill file, as the cup is usually made of a harder metal than the bb shell and thus could distort the entire inside threading of the bb shell.
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Old 09-17-12, 05:49 PM   #9
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Thanks everyone. I took the cup to Circle A Cycles here in Providence, RI and they cleaned up the threads nicely for me. Thanks for the info and help again
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Old 09-22-12, 12:14 AM   #10
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Get some valve lapping compund and slowly thread on working back and forth until it screws on easily. The threads will look new.
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