Bent BB shell - advice please
 

I have put in many countless hours restoring a '74 Nishiki Competion. After many months of stripping, sanding, filing, prepping, painting, sanding, painting, sanding, etc., I was finally ready to build up the bike up again.

http://i850.photobucket.com/albums/a...psbc022287.jpg

http://i850.photobucket.com/albums/a...ps55aa6f5e.jpg

Or so I thought. 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.

http://i850.photobucket.com/albums/a...psa5d6835c.jpg

http://i850.photobucket.com/albums/a...psc81eb757.jpg

:(

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.

File it
 

I think your best bet is to file as you suggested, just enough to be able to get a bb threading tool in to chase the threads. I doubt the bb will need facing, dent is probably not disturbing the bb face plane. The slight loss of full depth threads in that spot won't be a significant mechanical problem. I would not try to bend the bb from the inside or outside, only bad things will happen. IMO for all that.

Brian

^Thanks, Brian. I appreciate the input. I cross-posted this in the C&V forum as well. Among the suggestions there is to start with simply re-tapping the threads on the DS. Not sure if that will work, but it seems like a good place to start before doing anything more drastic/permanent. If the tap fails, I could always bust out the file, or possibly try re-tapping to the larger Italian threads.

Open to other suggestions if anyone has any...

re-tapping was my first idea. Not sure if it would be worth trying to bend it back a little. It's going to be tricky to get the tap to start right in its current shape

I dropped a frame on the head tube, it's amazing how much damage that will do.

I did this repair on a Condor frame I bought at a unclaimed/damaged freight sale. I used a $15 Harbor Freight muffler pipe expander . While heating the affected area I slowly tightened the bolt on the expander until the dent was gone. You have to do both sides individually . I chased the threads and repainted, It worked perfect.

http://bikeforums.net/attachment.php...hmentid=337580

What a bummer, that is a great paint job.....


no input....my only thought was coming in from the other side with the tap, but realized that would only work if it were already italian threaded

I'd get a six foot long 1" O.D. steel pipe, wrap 6" of one end with a couple of layers of denim from a pair of old jeans to keep from damaging the threads, and gently lever the dent out. The large diameter of the pipe should spread the force over enough area of the top edge of the left side of the shell so it won't distort the good side.

Buy a piece of 1 1/4" diameter round bar about 4" long in brass or aluminium. Cut a 3" axial slot in it with a hacksaw (and a lot of patience). Insert this into the BB with the slot at 12 o'clock in the third picture. Place the frame drive side down on the workbench so the slot is facing upwards. Use a cold chisel as a spreader in the slot and make like a blacksmith with a nice big hammer until the shell is round enough to accept the BB thread chaser. Chase threads, you'll be good to go.

Hire the slotted piece of brass round bar out to other C&Vers as the Gaucho Patent BB Straightener.

Thanks everyone for the input and suggestions. Local fellow forum member Toytech offered to grace my frame with his Campagnolo BB tap. This seemed like the simplest solution and least likely to cause damage to the threads, so that was my plan A before moving on to other options. Fortunately, that's all that was required. The Campagnolo tap went in without much of a struggle, and the BB is now installed. Whew. Crisis averted. :thumb:

http://i850.photobucket.com/albums/a...ps7c1d8d9b.jpg

Yeah! Great outcome.