So, what is it that typically makes the bottom bracket go bad? Is it bad cleaning/maintenance, too much jumping (I'm a borderline clyde), awesome wattage (I doubt that in my case). Or is this a part that's designed to fail so that more critical components, like the frame don't get harmed?

 

Internal BBs cannot really be maintained or adjusted. Cleaning is difficult as well.

The fail by water and grit entering the bearing and causing the cartridge bearings to get loose. This is felt by poor shifting or chain rub, and finally the bearing can get very stiff if the balls jam up inside.

External bearings can be cleaned and adjusted. Most have some sort of seal that can also be replaced. The cartridge bearings can also be replaced. The fail by water and grit getting inside the bearing...with the same result as internal bearing BB's.

External bearing BB's can be reset (tightened) to stop the sobbling, however once and adjustment is required the remaining life is not long.

 

In the last three shimano BB's I've pulled apart, the cause of failure seemed to be lack of grease and or water ingress.... Ie the bearings were dry and rusty.

So when I got the new bearings I pulled the seals off, and what was in the bearing? Not grease... well a token amount.

Needless to say I packed them all with fresh grease, I guess I'll find out if that helps...

 

One of the filthiest places on a mountain bike is right where the BB is located. It's the spot that gets all the dirt kicked up by the front tire, every drop of water splashed up by the smallest of water puddles, and a few hundred Watts of peak power concentrate at that one point to mash it all right into those poor little bearings. That's a lot of abuse BB's have to put up with, eventually they lose.

If you're paranoid about loosing a BB to dirt, you could easily make some dust seals to place between it and the cranks. Making the BB waterproof might take more effort.

 

Planned obsolescence ?

TIME TRAVELER!!!!!!

BUSTED.

I mean how else did you manage to post your response as the #1 post, and the original question is #2 now?!?!?!

 

Man, I thought my computer went wrong...I have absolutely no idea?!?!?!?

I´ve tried to edit and see if relocates with no success...mods probably will fix it?
Sorry for the OP

 

BB's are like chains,Cables, housing and tires, consumable. At least the industry has gotten away from including the machined BB spindle as part of that consumable part.

 

Doesn't really matter how much you baby your BB, it's some races and a pile of metal bearings so eventually that system is going to wear. The races wear, the bearing wear, dirt and water get in and cause faster wear, grease gets old and causes faster wear, and repeated bashing from hitting bumps and jumps will eventually wear flat spots in races and bearings. All systems will fail at some point, sometimes it will last longer if you spend more money and sometimes not.

 

Thanks for the insights. I really don't know jack about how modern bikes work, so I'm always interested in learning more, especially since I kinda have to take the shop's word whenever something breaks. On that note, how the hell do I learn all of these ins and outs anyways?

 

On that note, how the hell do I learn all of these ins and outs anyways?

I went the be a bike mechanic for a decade route. I can highly recommend it if you can afford to get paid very little. Otherwise ask around to see if your shops do any maintenance classes or you can even go to a professional class for that sort of thing. Or just keep playing with your bike and reading as much as you can.

 

Internal cartridge style BB's (square taper/ISIS/Octalink) are designed to be used and thrown away when bad. Up side is that they are not super expensive. Downside is they are not serviceable.

External BB's have a problem of not draining water out when it gets past the seals. This in turns, forces the grease out of the BB over time. Then its rust and bearing failure.

However, external BB's can be serviced. There is a sticky at the top of the page in this forum. I've serviced several Shimano and FSA external BB's without issue. Its not super duper easy, but it's not truly difficult either.

I'm currently using a Chris King BB and also bought the tool so servicing down the road can be done without trouble.

 

Internal cartridge style BB's (square taper/ISIS/Octalink) are designed to be used and thrown away when bad. Up side is that they are not super expensive. Downside is they are not serviceable.

External BB's have a problem of not draining water out when it gets past the seals. This in turns, forces the grease out of the BB over time. Then its rust and bearing failure.

However, external BB's can be serviced. There is a sticky at the top of the page in this forum. I've serviced several Shimano and FSA external BB's without issue. Its not super duper easy, but it's not truly difficult either.

I'm currently using a Chris King BB and also bought the tool so servicing down the road can be done without trouble.

Really old school square taper cup and axle BB's could be easily serviced, the problem was that they couldn't be sealed so you had to tear them apart and regrease after every
wet enough ride. ( Or maybe I just had more time to work on bikes in the 80's)

While modern BB's are more disposable, I consider them an upgrade in every other way. They just work until they don't and mostly are cheap enough to simply replace. If you've ever spent days trying to chase down that annoying creak in the BB, you know what I mean.

Isis and octalink were not well thought out designs, but I really like the new external BB hollow axle designs.

- Booker C. Bense

 

why does BB go bad ?

Because of bad manufacturing tolerances, frame BB shell widht, too much preload on assembly of the bearings, bad quality bearings... and also inadequate watter and dirt protection !

 

If you want your external bb to last longer, get good at taking it apart and cleaning. I do it every 20 rides or if it gets really wet, its not a big deal. But most external bb run sealed bearing units that are pre-greased and reasonably water tight.

As said before, they won't last for ever. I'm am industrial mech and live in a world that revolves around bearings and lubricants. These are engineered to be replaceable. No joke, 75% of my work is bearings, bushings and a good ol' greasin.

 

Same reason most parts go bad, neglect ! IMO

 

External BB's are virtually all killed by moisture.
The moisture sits in the crevice beside the bearing, rusts it's way under the seal and the bearing is toast.

If you think your BB got wet, pull the cups out and leave them to dry sitting bearings up in a warm dry place.
Or get one of my BB's with storm drains.