>>1873751They are not bad, or rather, there are good and bad ones, just like cartridge units. The smoothness and hardness of the bearing surfaces differs a lot between specs. However it's extremely rare now to find a loose ball bearing bb that does not have a pitted spindle which means it's worn out. Even the high end ones.
They still work obviously, actually they can still feel 'kinda smooth' at the crank with exploded ball bearings and pure black gunk. You can feel them best just turning the axle in your fingers. Or if there's any play it's a sign it's due a service. It's definitely a nice thing to service or replace, in almost every case. And you feel the difference riding if you're serious rather than just cruising about. But I wouldn't worry about it unless you feel the play, hear it clicking, or want to teardown the bike to overhaul everything.
One of the major advantages of cartridge units which last longer between services is you're not pressing your crank on and off nearly so often, which can cause headaches and wear on the taper. So leaving what you have is actually a safe bet in terms of 'damage' as opposed to your hub and headset bearings which you do not want to wear out and which servicing cannot do any harm.
It really depends on how nice the bike is. However I would not recommend a cheap cartridge unit unless you have no other good option. Look for an old stock UN55, the decent shimano one, which was discontinued recently and many bike shops still have cabinets of. Or spring for IRD.
If you chose to replace it or remove it to service and inspect, do some observations first. See how far your crank arms are from hitting the chainstay, how far the inner of your crank would be from binding on a cartridge that protrudes a little, and see how far your front derailer limits have adjustment in either direction. Spindle length is not an exact science and it's good to know if you'd rather have one slightly wider or slightly narrower.
