BB going bad?
 

My bike is making a subtle sound. I hear it when pedaling poorly (mashing). If I spin nice round circles I don't hear it. It makes a wiz or a zzztt sound. Is that a BB going bad after only 6,000 miles?

Not going bad, but perhaps dirt and crud in the BB. Maybe you need to repack the bearings.

Only 6,000 miles? That's about the life expectancy of a cartridge BB, correct me if I'm wrong.

I'd say you're very wrong. The most common problem associated with that sympton is loose crank bolts. The original poster needs to torque them to spec.

Or, it could be the pedals clicking, too. Remove the pedals and clean then grease the threads, then screw them back in and make it tight. At least you'll rule out a possibility this way.

If the problem turns out to be the bottom bracket bearings itself, not the pedals or the crank mounting on the BB, then you should just ride it into the ground. Typical Cartridge BB's aren't replacable, so use it for as long as you can before it starts to slow you down. In my understanding, the bearings usually go bad, the spindle rarely, rarely, snaps.

On my end, I've got a Shimano UN-52 (LX, square-taper BB) and it's got 8,000 miles and is still almost perfectly smooth. But it's on a road bike that rarely gets ridden in the rain or anything...

Ride it into the ground? I can't stand that clicking noise.

I agree that it's unlikley to be a bottom bracket issue. I've had occassional cyclic noises coming from the crank area and have always eliminated them by methods other than replacing the bottom bracket. And my current bottom bracket, on the bike I ride the most, has over 10,000 miles on it (Shimano cartridge).

On this same subject, what IS the projected service life of a cartridge BB? I just replaced the BB on a '74 Atalia with a UN-52 and doubt I'll get 30 years of life out of it. The Atalia is my 'beater', and mainly gets ridden of rough/dirt roads when I'm out with my kids.
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depends on the quality of the BB and conditions used. i've seen 6-month-old bikes with shot low-end Shimano BBs, and i've heard of Phil Wood BBs lasting more than 20K.

My understanding is that the Phil BB's typically go for 30,000 miles or more. Plus, their bearings are replacable, so the main unit could feasibly go for double or triple that with the bearings replaced. I'm considering getting a Phil BB.

Nashbar has 70mm UN-52 BB on closeout; maybe I'll get a couple to keep on the shelf...
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I don't think anyone mentioned this yet--it's quite common for a creaking noise to come from the lockrings that hold the cartridge in place in the BB shell. It can be remedied by taking the cartridge out, removing the rings on both ends, greasing the BB shell threads very well before reassembling the whole shebang.

Tighten the Crank first...

If your BB is a sealed unit, there should be no maintenance on the unit at all. Otherwise, (as others mentioned) , you'll need to take apart the BB and clean out the water and gook. there could be water in the crank (from poor washing technique or riding in heavy rain with little grease in the crank.

It could be the chain hitting the front derailleur. That would be why you only hear it when you mash. You flex the frame more at the BB and the chain rubs.

Bottom bracket life can be extremely long. I've had two Shimano BB-UN72's last 30,000 miles each and both were replaced because I was upgrading to something else and were working well when removed. These were on road bikes but subject to a fair amount of bad weather riding.

I've heard this noise (zzzzttt) when riding behind other riders too. In the pace line you can tell when the rider infront of you is accelerating because you hear the drive train get a little more noisy.

Problem solved: (emabarrassed) I oiled my chain a little more than usual.

Thanks for replying.