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I have a Tange 68x103 mm bottom bracket (pictured) that I plan to use in an old steel frame (building a single-speed/fixed). It turns out that my non-drive-side bottom bracket shell threads were a bit destroyed. My LBS was able to chase/tap quite a bit of it, perhaps enough to fit Hollowtech-style BB cups that they likely tested with afterwards.

However, the Tange BB has a very long left cup and it does not fully fit into my BB shell. I would like to somehow shorten it. Given that the BB cup has no lip on it, I plan to insert it in reverse on the non-drive-side, and then somehow cut it down to size, likely with a hacksaw. Is this a crazy idea? Does anyone have tips on ensuring the threads are preserved?

I'll likely cut off 6 threads or 1/4". From my point of view, the function of the cup would be preserved if I can successfully do this. Am I wrong?

Tange 68x103 BB

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Have you tried inserting only the LH cup? Or were the RH cup and bearings already installed when you tested it? –  zenbike Mar 25 '12 at 9:54
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So you're saying that the left-side cup doesn't go in far enough to firmly contact the cartridge, and by cutting off some threads you feel that you can achieve this firm contact? In that case cutting off the threads as you describe may be an effective fix. I guess I'd try using a very fine-toothed hacksaw, trying hard to not chew up the edge of the BB housing too badly in the process. "Chase" the threads afterwards with a small triangle file. –  Daniel R Hicks Mar 25 '12 at 12:38
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Inserting in the frame backwards to give a stable base for cutting, may make it difficult to remove once cut. –  zenbike Mar 25 '12 at 13:25
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@DanielRHicks About the threads, an idea I got recently was to thread the cup into the shell in reverse as planned, and then thread a cup-and-cone-style lockring onto the cup. Cut with a fine hacksaw, and then file the edge flush with the lockring. Then I can chase the threads by removing the lockring. –  fideli Mar 25 '12 at 16:04
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I hope you left some of the "hollow" that the cartridge fits into, vs filing all the way down to the shoulder that presses against the cartridge. If you grind all the way to the shoulder there's nothing to hold the cartridge centered as you pedal, and you'll have serious problems. –  Daniel R Hicks Mar 26 '12 at 0:58

2 Answers 2

Another alternative would be to find a LBS with access to "Sutherland's Handbook for Bicycle Mechanics" and find a BB with the appropriate measurements. Much easier, and quite possibly cheaper in the long run.

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For that, nothing beats the Velo Orange Grand Cru Threadless BB. Alas, LBS in Canada have nothing but a Norco catalog so can't get any parts other than run-of-the-mill. I've done enough eBay for this bike and I preferred not to wait for a new BB. Thanks, though. –  fideli Mar 29 '12 at 0:31

The RIGHT way to do this is to screw a STEEL bottom bracket lockring on to the BB cup BEFORE you reach for the hacksaw. You can then clamp the lockring in a vise (not the BB cup) and spin the cup in the lockring until you have the exact number of threads you want to remove sticking out.

Make the cut by lining up the hacksaw flush against the lockring so you get a straight cut and make the cut. THen you simply unscrew the BB cup out of the lockring. The threads in the lockring will repair the threads on the BB cup as you unscrew the lockring off the cup.

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You'd crush the cup in the vice, even if you clamped on the lockring (which would not provide enough "purchase" anyway to allow sawing). –  Daniel R Hicks Mar 26 '12 at 0:55
    
I intended to use a lockring but couldn't find one. Either way, I preferred to use the frame and reach from the other side with the BB tool. –  fideli Mar 27 '12 at 3:40
    
There is no right way to do this. And as Daniel points out, you way woul damage the BB. –  zenbike Mar 28 '12 at 2:53

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