I pulled a Praxis Alba crankset and M30-BSA BB from one of my bikes, planning to install on a project in the future but for now just to put on the shelf. In the process, I noticed that the crankset felt notch-y. Upon inspection on the bench, I tracked this down to the NDS cup / bearing (28mm) which feels rough / notch-y on its own.

Out of curiosity, I tapped the bearing out of the cup and it feels smooth on its own. Re-installed in the cup, back to feeling rough. With an apparent infinite amount of free-time, I slowly pushed back in and tested the bearing, stepwise, and found that the notch-y appears with the bearing about 3/4 of the way back in.

Questions:

1. Is this normal behavior for a bad BB bearing, or unusual? I wonder if the cup had somehow become ovalized to cause this, but perhaps I’m over-thinking it? Cup looks round…
2. A replacement bearing kit for the BB cups is about half the price ($22) of just buying a new BB. Am I fine buying just the bearing kit? I wonder if I’d be better off just spending the extra money and get the entire BB and install a new cup/bearing NDS assembly. I have a headset/BB press tool, fwiw, and am always looking for an excuse to use it.

I did a quick poke on the seals of the suspect bearing and it looked like potentially destructive surgery to get inside for a look.





I come from the land of C&V and have limited experience with external bearing BBs beyond installing to torque spec and then installing the crankset. Apologies if my question(s) are common here - I did a quick search and didn’t see a match.

Just replace the bearings, or if you feel like buying some extra time with the old ones; pluck off that seal cover, thoroughly clean the bearing and then repack with grease. I pluck the seal covers off of mine all the time using a sharp pen knife. They pop right back on and the bearings run like (almost) new for quite a while, depending on wear. Eventually you will have to replace with new bearings. If you look on the outside of the bearing you should find the correct part numbers. Easy Peazy. Have fun with that press tool, Smokey

solid steel isn't really solid.
when the bearing is press fit into the aluminum cup, the bearing's outer race shrinks in response to the external pressure of the cup.

the bearing is specially ordered to allow for this shrinkage.. if you order a bearing that has "the same size", it will NOT allow for the outer race shrinkage, and will "feel rough" soon after installation into the bike frame, which also causes a bit of outer race shrinkage.
A good Bearing salesperson will ASK what type of installation the bearing will be used in, and supply you with the Correct clearances for your intended use.. An idiot will happily toss the first one he or she pulls up on their screen at you, then take your cash.

want another bike-related indication of steel's flexibility? Set a bare front hub axle/bearings clearance up to a "Zero Slop" state... then place it in a fork and tighten the QR as you normally would.. then feel how rough and Over-tightened it feels when spun without a rim attached... The QR has COMPRESSED the front axle.

Thanks for the replies.

It sounds like ordering replacement bearings should be fine, so long as they are correctly spec'ed (i.e. from Praxis)

FWIW-the part number usually comes from the bearing's dim.s. I find the best deals on bearings thru Ebay, believe it or not and haven't had any problems with them. But there are many bearing houses thru out the world because the world revolves on bearings.

Praxis m30 has a 28mm id nds bearing which is just the 30mm id bearing with a sleeve pressed in. I haven't been able to find these not from praxis.