I have about 5k miles on my current BB, and was wondering if it's time to replace?

It's a lil' creaky (but always has been). It's an ISIS drive if that matters.

I know I'll be changing the crank at the same time, but my cassette still looks perfect.
I'm pretty meticulous about keeping my drivetrain free of abrasive dirt, and only use wax on my chains, so just what should I be looking for as far as "signs of wear"?

^^^^... as to the bb; How long is a rope? As for chain wear/replacement: learn to measure one for wear as per Sheldon Brown at www.harriscyclery.com

BB wear out a lot slower than cassettes and chains and should last at least as long as your chainwheels. The bearings are about the only thing that wear out and apart from untoward 'noise' in the BB, significant grittiness when rotating the spindle by hand (but compare with a new one before jumping to conclustions) and sloppiness in the in/out (axial) or up/down (radial) movement of the spindle in the housing suggest end of life. Essentially there should be no movement. A lot of BB are tossed well before end of life, especially with the splined types where positive lock of the crank to the BB occurs and there is little risk of bottoming the crank such as occurred on taper sq BB.
Steve

I knew some wizeazz would give me the "How long is a rope" comment!

And as for chains... yes, I know how to make sure they aren't stretched*

* and yes I know they don't actually stretch, but rather the pins/rollers wear - thus making them longer (cuz of the extra space created between the P/R's).

What I want to know... is general BB lifespan. Can I get that without the n00b treatment?

That's nonsense....The older quality square taper shimano shimanos might last as long as chainrings,but again,how long is a rope, and consider all the variables.The octalinks don't tend to last as long due to smaller berings,and alot of the isis types get an even worse rap. Some of the lower end stuff isn't even worth installing.

Truvativ Giga Pipe

Consider this:

I have two nearly identical Trek 4300 mountain bikes. Each have about the same amount of miles. (somewhere around 5000 miles each.)

Bike A: The bottom bracket went bad in the first 2000 miles.

Bike B: I have 5500 miles on that bike and the BB is fine. I will change it however with my upcoming drivetrain upgrade.

If you want generalities, than generally speaking, if it is a less expensive BB than change it very 5000 miles or so. That way you won't have to find out how long it lasts. (hopefully)

Another example of "how long is a rope?"

Bike A: Headset has never been touched.

Bike B: Headset went bad before i ever hit 1000 miles.

Can't give you an average ISIS lifespan, but my ride partner's BB died after about 6 months of hard trail riding-lots of loose rocks, drops and whatnot. Came with his '04 Gary Fisher Tassajara. Has Bontrager cranks, but I don't remember what make the BB is. Pretty damn cheap, evidently. He rode it much longer than he should have...let's just say we couldn't find any bearings when we finally took it out.

On the other hand, I have an early XTR Octalink that's still goin' after several years. I don't care for the spindle splines, but it still works. My drive-side crank just loosens up every other ride. Think I misaligned the crank when reinstalling it once. I still have an old square taper BB(LX maybe-UNBB-52, or somethin' like that) that's fine, too and I think it's older than the XTR.

Anyway, to answer your question, I guess it depends...on a lot of things. Just call me Mr. Obvious.

Thank you Ranger.
I get what you're gettin' at.

Basically, this BB is creaky/squeaky when under my considerable Clydesdale load, but spinning it by hand there is no grinding or noise, and is smooth as good scotch.

OK... now my crankset... should I be looking for "shark-fins" or just general "thinning"?

Is there a way to see how the chain sits in the teeth, that would tell chainring wear?

I tend to look for "thinning', mine don't always "fin". I also look at the chain on the ring(from above). If the tooth doesn't fill the link, I take a closer look at the teeth and chain, just in case.

It's funny.... my largest ring seems thin at the top of the teeth, but the chain does sit snugly in the cogs. As I posted previously, I'm pretty anal about grit in the drivetrain (it's actually soothing to have a post-ride q-tip session), and my chains are never worn.


Ohhh... and I like pie too. Especially apple with a thin slice of very sharp cheddar melted atop.

Granted, my experience is road, not ATB but I average out riding mileage on my two road bikes and one bent and the two octalinks have no noise or side/end play at 10-11kmi each and the White brothers on the bent just turned 11kmi, ditto.
Steve

This is road... I'm a self-sufficient tourer. (Bike Packer)

As a mountain biker, grit is my drivetrain sometimes. With the relatively lower mileage I rack up, I don't worry about it too much. Of course, I would probably clean my bikes like I used to(down to the bare frame) if my wife would let me keep them in the house.

Not that you had any idea of knowing, but the apple pie mention was a very low blow. I've never tried it with cheddar, but I can practically taste it now. I've sworn off sweets for the moment to try and reattain my fighting weight. Oh, the pouring salt, the twisting knife!

I have a small amount of grittiness that comes and goes, even though I repacked the bearings with grease. So how much is okay?

Bikepacker, I don't really understand waht you are talking about with the crank needing replacement.

If your chain isn't worn out, then there is no way that your chainrings need replacement.

Usually, in drivetrain wear situations, the chain wears the fastest ('stretches'), and the worn chain wears out the rear cassette cogs, as hey are smaller, and the chain rings wear out the slowest, as the larger teeth counts distribute wear better.

So replacing the crank/chainrings doesn't seem too logical if you chain isn't worn.

EDIT: On the BB wear issue, stock bbs tend to wear out pretty quickly, as manufacturers tend to skimp on bbs, as you really can't see them, or notice them until you have a problem. The stock bb on my trek 4300 went within the first 500 miles, mostly on road. ISIS bbs wear out quicker than square taper bbs.

Totoro: grittiness that comes and goes can be considered negligible. Grittiness that results in cogging while turning the BB spindle may not be. If you are using replaceable ball bearings and the races look clean on the cups and BB axle then grittiness should get better with replacing the balls. Balls are usually much harder than the races, so the races are more likely to wear. An unquantifiable 'little bit of grittiness' that comes and goes with hand turning can be completely ignored for practical reasons while riding. If you are repacking sealed bearings and they are gritty then you fall back on percieved noise while under riding torque and axial/radial play of the spindle when assembled in the bike. In principle sealed bearings are replaceable for bearing costs of $5-10 each.
Steve

Must be a trek

WARNING: Zombie thread

As long as the BB is well adjusted and kept clean and lubricated, it will be the hardest component to wear out on a bike as they have the biggest bearing areas and low RPM loads.
If still in doubt, just get yourself a fancy Phil Wood sealed BB unit that could most likely outlive two or three bike frames, per what I have heard about them through the years.

Chombi

You bumped a 5 year thread to add that?

Or a Felt, mine wore out at 18,000 miles

Will have to replace the bottom braket on my Cannondale BB-Ultra, here in the next month or so. It has 1695 original miles on it. The bb is a Shimano Octlink BB-ES25 if it makes a difference. I was kind of bummed didn't think I would have to replace that part for a long time, seems strange to me!!

sydney is still trying to care for us.