Cup and cone BB help

[BlackCat]

Thanks. Was mindful of this but unfortunately it’s not the issue. It’s so odd. The cup and cone screws in easily by hand but the sealed unit gets maybe 5mm in and that’s it.

Have managed to track down a 73/122 Tioga cup and cone, NOS, for a princely sum. If it isn’t the missing link in this nightmare, I’m going to liquidate my whole retro collection and maybe take up riding bikes instead of building them as a hobby.

Let’s hope things never get that bad.

 

[mattr]

Get the threads chased out at a bike shop (or borrow the tools from someone) there's probably 2 decades of gunk and/or surface corrosion on the threads. The shimano sealed unit is probably a top limit of tolerance and the CnC isn't...
The 1.37x24 TPI in 68/73 shells has been a thing for decades. The only other size that it could possibly be (being a US designed frame) would be italian. And then your CnC would have dropped in without even touching the threads...

 

[Tootyred]

Mattr is completely correct. The treads on the 2 bottom brackets will be the same, if one goes in the other should. It may well just be a tolerance issue.

If you can screw in the shimano one above then you new 73mm one ( I assume thats the same pitch) must do too. Try putting the first shimano one back in first, but only after you give the threads a good clean out.....try an old tooth brush or a small copper brush and run it round with the treads. That might clear enough gunk and filings to get it in.

Finally, be absolutely sure your running it in dead straight. Ive had instances in thebpast where someone has tried to fit a cup on the piss and got it in a turn or two before realising.....the old " true" thread path will still be there it will just be crossed over.

If none of that works then lbs or mate with a tap and set to clear it out.

All the best

 

[eshew]

Yeah chase the threads and doubly confirm you don't have it reversed. Might have done that a time or two.... Which is why I now own a thread chaser.

 

[BlackCat]

Thanks guys.

Update is that I have my new (old) Tioga.. and non drive screws in easily by hand. Drive is another story but whilst I can spanner it in about 90 percent fairly easily, it just doesn’t look completely parallel with the bb shell. It’s not far off but I know that if I applied force I could drive it to the shell, but it wouldn’t be flush. Weird thing is that it screws in pretty easily to that point. Grrr.

Will have yet another crack at it in the daylight. Seems to screw in parallel but maybe I need to fully check all the way round the bb shell because I must be a degree or two off. I guess.

 

[Tootyred]

If you can borrow a kit like this, it also has facing cutters in it....im not suggesting facing the drive side if its on the piss for some reason, but it will help show if the theads are parallel.

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[BlackCat]

Thanks for that. It’s a good idea but I wouldn’t trust myself. Anything that involves cutting into the frame is something I would 100 percent screw up and regret! What’s left of the Kara would be back on here as karma or “wall art” inside 24hrs!

I think I’m now about to throw in the towel and march in shame to the LBS.