5

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 http://www.benscycle.net/bmz_cache/a/a1a0837709b9deb5702d1c46199e4f77.image.700x524.jpg

Improve this question
8
  • 1
    Have you tried inserting only the LH cup? Or were the RH cup and bearings already installed when you tested it?
    – zenbike
    Commented Mar 25, 2012 at 9:54
  • 2
    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
    Commented Mar 25, 2012 at 12:38
  • 2
    Inserting in the frame backwards to give a stable base for cutting, may make it difficult to remove once cut.
    – zenbike
    Commented Mar 25, 2012 at 13:25
  • 1
    @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
    Commented Mar 25, 2012 at 16:04
  • 1
    All, it worked! I actually couldn't find a lockring so I just hacked at it against the BB shell. After cutting the excess thread off, I filed the cup until I reached the BB shell edge. The starting thread is a bit finicky but it didn't feel like it was grinding. Afterwards, it threaded up against the cartridge without issue. No pictures, sorry! Was too excited to get on with the rest of the drivetrain.
    – fideli
    Commented Mar 25, 2012 at 23:01

3 Answers 3

Reset to default
3

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.

Improve this answer
1
  • 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
    Commented Mar 29, 2012 at 0:31
2

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.

Improve this answer
3
  • 1
    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
    Commented Mar 26, 2012 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
    Commented Mar 27, 2012 at 3:40
  • There is no right way to do this. And as Daniel points out, you way woul damage the BB.
    – zenbike
    Commented Mar 28, 2012 at 2:53
1

If you're committed to square taper cranks, I suggest purchasing a threadless repair bottom bracket. there's a company, YST, that makes them and these days they're not too expensive and work pretty well. You might need to retighten it occasionally, but I've had big guys use them on daily commuters with little or no issue. Loctite on the threads will help.

But I'm curious why it won't thread deeply enough into the NDS side of the BB shell. in every instance of bad BB threads i've encountered (and there have been plenty), the problem was the opposite - that there was nothing there to grip to at all, let alone block the cup!

EDIT: btw, whatever you do, i would definitely avoid cutting the cup. BB shells are made from massively hardened steel. at my shop we have a bucket full of loose cups, you might be able to find one that works at your LBS (though they are mostly all the same size tbh).

Improve this answer
2
  • 1
    Wow, this brings back memories. I did indeed cut down the NDS cup of that bottom bracket for that project soon after posting this question and I remember having to finesse threading the shortened cup into place, but it worked and bike is still going strong 8 years later. I don't remember whether I looked into threadless BBs at the time, but they're on my radar for cases that need them. I'm always on the hunt for an old steel bike project although I don't have as much time these days as I did when I posted this question.
    – fideli
    Commented Jun 28, 2020 at 21:48
  • 1
    i didn't even realize how old this question was, and have no idea how it came up for me. glad it worked out!
    – Nathaniel Hoyt
    Commented Jun 29, 2020 at 23:00

Not the answer you're looking for? Browse other questions tagged or ask your own question.