70slibrarymusic

Another newbie thread coming thru. So I just bought a brand new UN-300 from LBS and as I was testing it out just gently hand-threading both sides on the BB shell, I noticed there was a bit of a snag on the NDS cup. Tried exerting a bit more effort than gentle and it was still turning so I figured it must be ok. I was doing this very gently because this is a repainted frame I just bought for cheap and I wanted to check if the BB threads were good. DS threaded in nice and smoothly going all the way in with no tools, NDS was the same until I got to the problem mentioned above. Inspected the BB shell threads and it seems good but I saw this on the brand new bottom bracket.



Did a bit of searching and found similar problems re: UN-300 having a hard time threading in but none that showed damaged threads.

Are BB threads this fragile that even hand-threading could damage them? I didn't use any tools and no real exertion of elbow grease this time. Already contacted the store asking for a replacement but I'm also thinking if the threads on this frame is damaged enough to have also damaged the brand new BB. Thoughts?

P.S. Can I also just force the BB onto the frame? I have yet to use tools or any real force.

jamesdak 

Looks like just build or something in the locking compound. I don't think it's a damaged thread.

RustyJames 

I would take it back to your LBS for a replacement.
Real world, if it started to thread in with the proper tool it would probably work fine.

Dylansbob 

Looks like alloy cups and far enough into the threads that I doubt it'll cause any problems. The threads will probably clean themselves upon installation.

clubman 

You're saying that's it's the NDS side but it's labelled as a left hand thread??

oneclick 

That will neither affect the strength of the cup, or (almost certainly) be the cause of the difficulty you are having screwing it in. None of the thread damage extends into the space where the matching threads of the BB shell will be.

I suspect rather that you have the fixed cup screwed in tight, and because of manufacturing tolerances or wear the non-drive-side end of the assembly is just slightly out-of-line with the cup itself. Those cups have a portion just the right size to accept the bearing, and inboard of that that a slightly larger diameter. If the assembly end is even a little out-of-line it can catch on the step between the bearing seat and the inner larger diameter portion.

To avoid this I install the drive side cup but do not fully tighten it; then I install the non-drive-side cup far enough to get the bearing correctly lined up and inserted in the bearing seat, then I fully tighten the drive side and finish the non-drive-side after that.

madpogue 

Interesting; but visually, the threads appear to be right hand thread.

dddd

There are low-end Shimano bottom brackets that thread in from the left, clockwise, until the NDS flange bottoms on the shell.

Then, the "adjustable" (i.e. floating) cup threads into the drive side end, CCW.

Yes, they are backwards, but the printing on the cartridge body reads from left to right as installed, and the cranks end up where they should be (if the cranks and bb are properly paired).

70slibrarymusic

Correct, the text goes in first, so the arrow points clockwise to tighten. Sorry for that, might've misled some people.

Thanks for all the replies guys! Can't wait to ride. This forum is the best. ​​​​