Resistance when inserting new BB-UN-300 by hand on drive side. Old UN300 and original FSA BB go in fine. Is this normal?

Question

I'm trying to install a BBUN300 on an old(8 years?) bike. The old BB-parts thread in like butter and fit perfectly (so threads cant be bad). The new UN300 threads nicely but feels like a looser fit than the orignal on the NDS.

On the DS i get significant resistance after only a turn or two and I cant go further by hand or with an adapter tool in hand. It doesn't start well/easy either. An old used BBUN-300 threads in nicely on the DS at least on half of my attempts.

Is this new UN300 a bad unit or are new BBs like this. Can't remember from last time I installed a new one and seems wierd since both old brackets go in so nicely by hand.

Answer 1

I tried another UN300 bought the same day from the same store (I didn't want this unit to get greasy as well for no reason initally) and it went straight in on the first attempt. My conclusion is that this must be a manufacturing issue. Installed the one that fit, returned the other.

It was no visual defects on the one that didn't fit, but my impression (desperate for reasons) was that the angle of the thread was not as steep as the original and the one that was installed(which is why I finally risked greasing up this one as well for potentially no benefit). Another option is that it just had a very slightly larger diameter, but either way it was a clear difference between the to units that was supposed to be the same.

Hopefully a useful post for someone else in the future. (Who suspects these kind of issues with machined parts in these modern times from a reputable brand?)