Mastodawn

#Biketooter #advice please:
Bottom bracket was clicking, then creaking, then creaking constantly, so the plan is to switch from a cartridge BB, to HollowTech.

I was prepared to use a long pipe/forklift/gorilla to break the BB shells loose, but it only took one Oomph with a large spanner to get them moving. Is this a red flag? Or acceptable on a bike that's only 1 year old?

Then I noticed that the part #, size etc. was ground off the cartridge, so it won't be trivial to identify a replacement (if the HollowTech doesn't work for whatever reason).

Then I found why the middle of the cartridge was scraped - a huge weld blob inside the frame.

The new HT will clear this, but if I go back to cartridge is it a good idea to do some judicious Dremeling to reduce the size of the blob? Is that blob any cause for concern?

#BottomBracket #cycling #maintenance

isol Dec 23, 2024

I have more questions - is it OK for the drive-side bearing to be only halfway into the cup?

The lengths of the axle ends is very different - I thought the whole assembly was supposed to be symmetrical or close. This cartridge definitely isn't.

#BikeTooter #maintenance #cycling

Niklas Dec 23, 2024

@isol the drive side needs more clearance for the chainset.

nick Dec 23, 2024

@isol err, nope. The bearing should be right in there where it belongs. Has the cup built up some kind of shoulder or distortion from wear?

UPDATE: that spacer / sleeve in the middle looks ... just a little bigger than normal? Like usually it's the same OD as the bearings I think, or maybe a smidge smaller?

Kris Hardy Dec 23, 2024

@isol The drive side bearing should be fully within the cup, and the lip of the drive side cup should be against the bottom bracket shell when the bb is installed. The bike wouldn't have been rideable with the bb shaft in the position you're showing, so I'm assuming that it shifted when you took it out, and the cup is now warped. Sorry for the question, but did you use the right tool to take the bb out?

Kris Hardy Dec 23, 2024

@isol It's likely that bb cup is warped into a slight oval, and the bearing will only fit in now if it's at just the right angle. I'd personally not try to reuse this bb.

Kris Hardy Dec 23, 2024

@isol That said, it can be a very close fit between the bearing and the cup.

isol Dec 23, 2024

I've had a closer look at the cleaned BB, and there appear to be witness marks showing that the bearings were fully seated (non-drive), and mostly seated (drive).
There are no horizontal scratches on the shell, which I'd expect if the weld blob had grabbed something during disassembly, and pulled things apart.

The point about distortion, and the bearing now only going back in in one specific orientation, is not something I'd thought of.
Maybe the bearing fit wasn't very close, and it just came out during disassembly … ???

Edit: that might be a fully-seated witness mark on the shell, drive side. 🤔
I guess I'm puzzling how the bearing came out so easily, when I was expecting hydraulic presses, or at least vigorous hammering, to be involved if I wanted to remove the drive side cup.

Kris Hardy Dec 23, 2024

@isol My experience is that you should see the witness marks on that inner shell on both sides. So, my suspicion is that the blob pushed the inner shell so that it was crooked. The assembler thought it was pushing the bearing into the cup, but instead it was pushing against the bearing and getting hung up on the cup, so the bearing didn't fully seat. They then cranked down the nondrive side cup as far as it would go but weren't aware that things were out of alignment. What crankset do you have?

isol Dec 23, 2024

I believe so - I used a tool which fitted snugly into the splines, and the holder-on to keep the tool in place.
There was no drama at all in the removal, not even any significant exertion.

Kris Hardy Dec 23, 2024

@isol That's all good.

isol Dec 23, 2024

OK, I have a theory as to what happened, based on your comment about the bearing moving during disassembly.

I'll assume that the force needed to press the bearings onto the axle is greater than the force needed to press the bearing into the cup.

The weld blob was digging into the sleeve, holding the cartridge in place. I expected to need a lot of effort to undo the BB, so had started with a long-handled spanner, giving more leverage.

As I unscrewed the cup, the weld blob held the sleeve immobile, which pressed against the two bearings connected via the axle.

As the cup unscrewed out of the frame, it also unpressed itself off the bearing, until there was enough play for the whole BB to come out.

Because I was spinning a large spanner around, I didn't notice if there was more resistance initially, and then less when the weld blob lost grip.

So, instead of the bearing being loose, or not pressed in initially, I now think that I unknowingly used that weld blob to hold the sleeve, and partially unseat the bearing as I unscrewed the cup.

Whew! Now it all makes sense (to me), and I'll be able to sleep tonight. 🤪

Kris Hardy Dec 23, 2024

@isol That makes sense. I've been able to push the bearing into the cup by hand on all the BB s I've had, so I still wonder if there's something wrong with the cup. The bearings are usually press-fit onto the axle iirc, so they shouldn't come off by hand (if they do, it shouldn't be a big issue since there is a tapered flange on the axle that the bearing seats against.)

Kris Hardy Dec 23, 2024

@isol Like others have said, the bb shaft length isn't going to be symmetrical.

nick Dec 23, 2024

@isol I think the only things you need to identify the original tapered axle BB is the axle length, everything else is pretty much standardized. If the new BB is an external bearing type you may need someone to machine down the outer edges so it can seat properly. As for the blob, I guess you could clean it up with a die grinder but cleaning the resulting crap up might be a drama.

nick Dec 23, 2024

@isol This comment turned out to be hopelessly naïve ... I've just been lucky to be living in a tiny corner of the Shimano world
https://www.sheldonbrown.com/bbsize.html#shimano

Sheldon Brown's Bottom Bracket Size Database

A database of bottom bracket sizes for various bicycles.

Andrew Bartlett Dec 23, 2024

@isol I have replaced a bottom bracket only because a new crank needed it. Given the weld blob I think you have a clear case for a warranty claim, clearly a manufacturing fault.

😀🚲Dec 23, 2024

@isol greased threads that are in good shape will stay tight and yet come loose with similar force. Was that weld blob making noise? You could probably clearance it with a file but worth some effort to keep the threads clean if you do.

Davva Dec 23, 2024

@isol
Measure the width of the bottom bracket shell (frame), and the spindle length of the BB. That's all you need to replace the BB with the correct size.
More info on BBs here - https://sheldonbrown.com/bbsize.html

Sheldon Brown's Bottom Bracket Size Database

A database of bottom bracket sizes for various bicycles.

Davva Dec 23, 2024

@isol
It'll be the blob of weld that has scratched off the make and model of your old BB. And will have moved parts of it apart as you removed it.
I'd file/sand it down if possible.

Kris Hardy Dec 23, 2024

@isol Just using the large spanner should be fine, but there are torque specs for the bb you should follow. The threading of the bb are made that way so that they do not loosen during riding (as long as they are sufficiently torqued during installation).

Kris Hardy Dec 23, 2024

@isol I'm not a pro mechanic, but that weld blob is concerning to me. You might want to talk to the manufacturer about it is this is a new bike or a valuable frame. If it's a beater and you're not worried about the frame life being affected, I'd Dremel it with a sanding drum, being very careful to only take off as much as you need, don't let the metal get too hot (hotter than you can touch), and absolutely don't have leave any sharp points or seams (places where there could be stress risers).

szakib Dec 23, 2024

@isol
- If it's really a year old, just get them to fix it under warranty?
- the blob needs to get removed
- if you switch to HollowTech, you will have more problems (related to wear). I would measure the various dimensions of the current BB and get a Shimano replacement one.

isol Dec 23, 2024

I have read that changing to Hollowtech isn't necessarily an "upgrade".
I'm doing this experiment because I got a good price on a crankset which 1) has shorter arms, 2) has a slightly larger big chainring, and 3) is HollowTech, so I can see whether 1 & 2 help me (short, slower cadence rider), and I can try HT while still having the option of returning to the original configuration if I want.

szakib Dec 23, 2024

@isol I have experience with both. The bearings in the HollowTech BB can be replaced, which is good. But even the cheapest square type BB lives 5-10 times longer than those bearings, and if you want non-shitty bearings, they are expensive. (Last ones I got were 40EUR/piece, but I need them to be able to take Finnish winter.)

David S (inactive)Dec 23, 2024

@szakib @isol this is very true. Square taper sealed BBs are very durable and not very expensive. Only benefit IMHO to "modern" BB systems is cranks that take power meters (if that's your kind of thing) and of course a tiny amount of reduced weight, albeit negligible in the grand scheme of things. I have a SRAM GXP BB that's creaking after a few hundred miles. My old commuter bike has done 10000+ miles on a UN26 shimano cartridge BB and is still going strong.