BB pulling out of shell

Building up a NOS track frame and went to put the bb in and found the the driveside threading seems to be too shallow. The non-ds threading fine, and the bb threads in smoothly, but on the other side I can push the bb in and pull it out with turning it at all.

Is chasing the bb shell going to help this at all? Or is this a more terminal problem?

Obviously, it is a BB30 frame with a BSA adaptor in the NDS. Chase the shell only if it is running away.

Do the threads look damaged ? If the non drive side is ok it sounds like they might be. chasing won't help if there isn't enough material to thread the BB into

If so I've been using one of these threadless BB's there are loads on ebay too, but I can't provide a link from my work laptop i'm afraid. You need two BB tools to fit them but mine have been good for about 2000 miles before they fall apart.

http://www.sjscycles.co.uk/prestine-threadless-68mm-sealed-bearing-bottom-bracket-for-frames-with-damaged-threads-prod16505/

Thanks for the link. The threads look fine, just too shallow. The frame had never been built up so have to assume they were just crap from the factory.

The frame isn't French or Italian is it? Actually, what is the frame?

Start from scratch: (accurately) measure the width and diameter of the shell, then post the details here together with what is written on the bottom bracket.

It's not easy trying to diagnose things remotely: no details and no photos just make it even harder.

I haven't got a set of callipers, but measured the shell as 69mm wide x 37mm diameter.

The frame is a Davanti, which as far as I know is a generic alloy frame branded by a bike shop here in Holland.

The bb says BB-7420, BC1.37x24T, 68. It's sold as "FSA RPM JIS Square Taper Bottom Bracket BB-7420AL BSA-68-ST"

I've added a photo of the threads as well.

1 Attachment

Yikes. Is it is weird (Italian) BB thread? Near the bottom of the page of this link.
https://en.wikipedia.org/wiki/Bottom_bracket
The giveaway would probably be the right hand thread on both sides.

Otherwise (and really unlikely) it is a manufacturing error.

Pretty sure you have an Italian threaded bottom bracket shell.

It's long been common for Dutch shops to source the bikes they re-brand from Italian builders.

If you had calipers, I think you'd find that your shell measures 70mm x 36mm and the DS has a right-hand (ie "normal") thread, rather than the left-hand thread you find with British/ISO BB.

As the BB you have is British the diameter is less, so the cup falls through the shell.

Why does the NDS engage? Manufacturing tolerances I'd guess: it screws in, but I bet it's pretty loose.

What you need is an Italian threaded BB: instead of "1.37x24T", look for "36x24T". If a BB isn't specifically listed as "Italian", then it's likely "British".

Have a look a Sheldon's cribsheet for more info: the table at the bottom shows you what happens if you mix the wrong shell and BB.

Thanks for that, I never would have thought of it not being British threads.

I guess I'll get it down to a bike shop to get the threads cleaned up anyway, and hopefully they have an italian BB I can try out.

I have a Sugino Messenger crankset that I had planned on using, but I might have an issue with finding a JIS bb with Italian threading? I've never ventured into the world of Italian standards, so don't know if they're compatible with Japanese/British standards at all.

I guess I'll get it down to a bike shop to get the threads cleaned up anyway,

Make sure they have the correct tool. I've seen bike shops use one half of the thread reamer for a bsa threaded shell in both sides of an italian shell and fuck the frame.

That would be a problem. The threads look fine an Italian thread bb is not hard to find which type do you need.

No probs with availability. Shimano UN55 Italian thread bb from CRC is £12.49 - in 107, 110, 113 and 115mm spindle-length.

That would be ideal.

I will need to recheck the required chainline for my cranks (Sugino Messengers), the internet had told me I needed a 103mm spindle, but hopefully it was wrong.