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I own an old Raleigh steel frame ('89) and wanted to install a cartridge bottom bracket (Shimano UN55).

I noticed it was difficult to fit it in the housing. When installed, the square taper shaft showed considerably more friction when turned.

Also, when I took the BB out again I saw rubbing marks on one side of the inner face of the lock ring, but only on one side. The threading itself is not damaged. When installing only one side of the BB, everything goes in smoothly.

To me it looks as if the BB housing is somehow misaligned. How do I measure it? And how do I treat it?

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  • A framebuilder with a rig may answer that question. Also check the frame for impact damage.
    – Carel
    May 3, 2020 at 11:40
  • How was the BB difficult to fit? Did the cartridge go in easily from the drive side? Was the lockring difficult to install? May 3, 2020 at 12:10
  • lockring was difficult. I had to install the cartrige half way, then add the lockring half way, continue to tighten the drive side just a little, then the lockring again. Repeated the process untill cartridge and lockring was fully seated.
    – user430
    May 3, 2020 at 12:17
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    @Criggie cleaned and greased. Threads look fine
    – user430
    May 3, 2020 at 12:29
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    @user430 That sounds like drive side (or actually whichever side the cartridge goes in, usually drive side) thread misalignment. May 3, 2020 at 14:19

3 Answers 3

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The two sides of a threaded shell showing axial or angular misalignment like this can usually be repaired by chasing and facing the shell with the normal procedure. Essentially what's happening here is the cutter on its pilot makes a new path for the threads to clear up the effects of heat distortion.

One could contrive a scenario where the two sides' threads were machined out of alignment from the start, but in practice it's not very likely, and distortion from brazing/welding is almost always the culprit.

There aren't any real alternatives to a proper piloted BB tap/facer set here. For most people it's going to be a shop fix.

Sometimes it's parroted that cartridge BBs made shell prep less important, but this is the counterpoint, as problems like this with mating the large amount of contact area between the cartridge and the adapter cup can keep the whole thing from working right.

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The threads on bottom bracket shells can have angular misalignment. The threads are typically cut in two operations, one from each side. If the shell is not aligned properly in the jig when the threads are cut misalignment is the result.

Misalignment should be fairly easy to diagnose at least.

Install the cartridge only from the drive side making sure to not cross thread it. If you look at the non drive side you should be able to see if the body of the cartridge is centered in the shell on that side. That will tell you if the drive side thread is aligned.

You can also install the lockring and see if its flange lines up with the edge of the shell (this is not a great indicator of thread misalignment , because the edge of the shell may not be true).

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    Of course back in the day a cup and cone bearing set would have hidden a lot of misalignment, that can't be hidden so easily with a cartridge.
    – Criggie
    May 3, 2020 at 12:23
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It could be just cross-threaded, that is quite common. Or it could also be misaligned.

If it is not way too off, facing the shells and tapping the threads (especially when cross-threaded) again might help. An individual who does not built new bikes is unlikely have the tools, but it should be doable in your local bike shop.

These tools allow the threads to be well aligned. It is not cutting each from one side separately but in a single process on a single common shaft.

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  • That's the heavy artillery for a one-off occasion and those tools are also rather expensive and require a trained user. Something I'd rather leave to a pro mechanic in this case.
    – Carel
    May 3, 2020 at 19:57
  • @Carel The answer does mention that an individual is unlikely to have them but a bike shop should. Unless the individual builds new bikes and has to clean the shells from the paint, that is. May 3, 2020 at 20:12
  • Maybe I need a stronger cup of coffee... but wouldn't misalignment from the factory be perpetuated by this facing tool, which uses the shell threads to align the shell inserts which in turn align the tool's rotational axis? Any misalignment in the tool's axis would be manifested in the face. What are the tolerances on the threaded rod?
    – Tim
    Feb 3, 2021 at 13:24
  • @Tim No, the shall threads are re-cut by the tool. The alignment is done by the rod. The cutting material is much harder than the threads in the BB shell. The also have to be sharpened often (and not cheaply). Feb 3, 2021 at 14:14

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