As some of you may recall from various updates I've posted over the past few months, I have been restoring a Nishiki Competition. When I bought the bike, it was in fair condition with some pretty serious rust issues. Even after a couple oxalic acid baths, the rust spiders were so pervasive that a repaint was necessary:





After many months (I work slowly) of stripping, sanding, prepping, painting, sanding, painting, sanding, decals, lug lining, painting, sanding, etc., it finally looks like this:








Here's the problem: During the painting process, the frame fell from a hook and landed on the BB shell. I was relieved that there was almost minimal paint damage when the frame fell. But I didn't notice that the BB shell itself had been dented. I only realized the problem last night as I went to install the fixed BB cup and start the build. You can see the slight deformation in the photo below. The threads still appear fine, and the NDS adjustable cup goes in fine. The dent is perhaps 1/3" deep or less than halfway into the threads.







I am worried that if I try to bend the shell back into shape from the inside, I will bugger up the threads. If I try to reshape the shell from the outside, I will likely mess up the virgin new paint job. Another thought I had was to file away at the dent/threads on the inside of the shell so that the fixed cup can then fit into the shell (e.g. just as a the top of a steerer tube has a flat section without threads going around the entire circumference).

Thoughts, advice, suggestions.

P.s. Cross-posting in the framebuilders forums as well.

If the cup goes in ok. maybe chase threads and clean up the face and it will probably be fine.

Ugh! Those fixed cups are pretty hard. Any thoughts on heating up the shell a little on the inside and using the fixed cup to reshape and hopefully preserve the threads in the shell? I guess it could all go bonkers and then you would have a bigger mess. The new paint job looks awesome!

Yow! That's a tough break and a real puzzler, too.
I don't think grinding off threads is the way to go until all other options are exhausted, but you may be at that point.
The only tool I can think of that *might* offer the ghost of a change is something like the expand-o-mandrels that muffler shops use to make pipes round again...I don't think they can expand with enough force to work in this case, however. And they usually require twisting around which isn't thread-friendly.
So...another possibility is milling out and re-tapping the shell for an Italian cup on just the one side (or both if you want to go there) and that could be your back-up plan if grinding out just a section of the BSC threads doesn't work out with the original cup.
Good Luck!!!

^Thanks for the advice unworthy1.

More input/ideas welcome.

No, the fixed cup does not go in, hence my dilemma. (Only the adjustable cup on the NDS goes in.)

I think I'd try to get a regular BSC BB shell tap in there and just work it like mad. if you're lucky it might recut and reshape the opening enough to work. I think a tap will have more beef (and huge handles) that a little fixed cup and wrench just can't provide. Use plenty of cutting oil.
If that fails then you can move to plans B, C, etc.

What about trying something like this?



https://www.amazon.com/Lisle-32500-Ex.../dp/B0002STSNU

All things considered, I'd go with the grinding thing. It would be damn hard to bend that back out without damaging the rest of that area. I don't think it would compromise the strength.

A small tailpipe expander wrapped with a layer of thick leather (to protect the threads) would probably make a clean repair

I will check and see if I have an expander, I just might.

careful persuasion with a brass drift punch may be enough to straighten that edge too, followed my a tap to clean up the threads.
The trick would be to not hit the frame with the hammer in the process doing so without at least marring the finish on the bottom of the shell seems iffy though.

It wouldn't make it perfectly round, but...
You could take an old fixed cup, cut out a small section of the threaded portion. Sit this inside the cup, engaging the threads. Protect the outside of the BB shell with something, and bend with pliers/vice grips/etc. Idea being that the piece of old cup protects the threads while you bend things back out.

I don't think you've thought that one through. Cutting out a small section would not allow the cup to be inserted.

How about a section of 2x2 lumber about 3 ft long? Lay the frame flat on the ground, slide the 2x2 into the shell, and "lever" it back into shape. The wood won't damage the threads, and if you get it bent back enough to get the tapered tap in there, you're all set.

I would post this thread in the framebuilder's sub-forum. Maybe even one found on another site that is more active.

Actually this approach looks promising. If you cut a slit through the fixed cup, you can probably thread it in. You can then apply force to expand this cup so the threads are protected.

Maybe another approach is to insert an aluminum sleeve (with a slit) that barely fits, then try to expand it to reshape the shell.

If I understand the post (which I believe I do, as I was going to say the same thing), he means cut out something like a pie-shaped section of an old cup, place that in the shell, and, with the shell braced against something solid, hit against the cup section with a punch.

I like the slit cup idea. If something with a suitable taper could be found, you could bang it into the spindle hole to expand the cup.

Air hammers do a fantastic job of applying force to an object without stressing the attaching parts. so, if you could get a round bit you could probably get the dent out. It would damage the threads.
Plug your ears!

Thanks everyone for the input thus far. I really appreciate the collective brain trust in action.

Colonel J: Yes, I did cross-post in the framebuilders forum here.

So far, the only recommendation from over there is from Calstar, who says to file away just enough from the damaged area as I originally suggested:
I think the 20grit's idea to use a slotted BB cup may have some merit. However, it may be a lot of work to cut up an old fixed cup and then I'm still not sure I could get it to thread into the shell while the dent is still there. Hmmm...

So far, I like unworthy1's suggestion to start with a regular BSC tap and hope that it can re-cut the threads deep enough to screw in the fixed cup. At least that option is not as likely to cause any further damage. Then I can move onto more drastic measures if that fails.

Maybe a threadless cartridge bottom bracket might fit without too much fuss?

I would try to use some wood and a hammer to knock it back. If you use a hole saw with the same diameter as the bottom bracket to make a U shape in a 2x4, you can use that as a rest for the bottom bracket. Another long piece of wood to put on the bent, threaded area, and a dead blow hammer to hit it with might do the trick.

get a piece of hardwood and drill it out with a hole saw to the required diameter. A mill would be best, but a good drill press could work. Then cut it in half with a band saw. Proceed to vice. This should take out some of the deformation but not all of it, but it could be enough to make it usable. The frame looks amazing and your efforts show. The finish is probably nicer than original. I like the tail pipe expander idea with leather too... I would do that with it clamped in the wood blocks.

You've got too much work into this to mess it up. I wouldn't even attempt trying to pound it back into place if you want to save the finish. Leave it, get a good shop to re-tap it and use the Park BB facing tool (basically a face reamer) to clean and square up the BB shell surface - I reckon this should be done regardless to remove the paint that you really don't want behind the fixed cup.

How will cutting a section out of a threaded cup allow him to insert it into the shell?