Bicycle Mechanics - is replacing bottom bracket bearings considered "routine meantenance"?

For a crankset with outboard bearing cups (eg., Ultegra 6700, or FSA Mega Exo) are the bearings something that ought to get replaced with any sort of regularity, or do they just need replacing when and if they start to go bad?

I.e., do you replace these bearings every 5,000 (or 8,000 or 20,000, whatever) miles, or do you just wait until they start to suck tangibly/audibly?

the good sealed stuff should last a really really long time. replace only if and when they actually show signs of failure (crunchiness, etc).

Ride it till it's worn out. it's hard to tell when they need to replace them (as in preventative maintenance), if they feel as though they are worn, then it's already time to replace.

For how long they last, it's also pretty hard to tell, I have 10000km+ on a 6700, and it's still smooth, on an MTB, replaced a Raceface one last week, which had done about 18 months in all weathers off road, the Deore which had preceded it lasted about half as long before it seized.

External BB bearing are marked (on Shimano) as do not dismantle, it is possible to take them apart, and you can buy replacement bearing from Real World Cycling http://www.enduroforkseals.com/id227.html among others. Is it worth it? when the cost of a complete new BB is the same or less that the bearing kit, not really.

Yeah. They're pretty much disposable. Fortunately, with outboard bearing it's very easy to swap out the cups.

Do yourself a favor though and buy this style of tool:

http://www.cambriabike.com/images/product/large/park_bbt-19.jpg

That one's a Park BBT-19. It engages better and pretty much eliminates tearing up the cups provided you have it in all the way. You can also attach it to a ratcheting handle if you want. The end of my Park chainwhip fits the hex side, so I use that.

On most of these cartridge bearings there's no option for maintenance. Consider them sealed modules that are used until they die. If you have good hand skills, it's often possible to pick off the seal without damaging it and thereby service the bearing, or in some cases you can replace with bearings sealed on one side only, allowing future service.

Otherwise use them until they die, which varies tremendously based on bearing quality, seal integrity, weather, environment, and total rigidity of the system vs. riding style. Some people get 10s of thousands of zero maintenance miles, others can't get a season.

Cool, thanks all!