how long do bottom brackets last?
 

after 4 years and maybe 3,500 miles i was told the bottom bracket needs replacing, i don't doubt them but i thought they were sealed? water and sand, dirt etc in there.

whats the best way to clean it?

The answers to your questions is that it depends. The more strength/weight/load a BB sees the faster it wears. The more rain/wetness/washings (especially with a pressure spray) the faster they contaminate and the lube degrades. If the frame isn't well prepped or made the bearings can loosen and/or be cockeyed to each other and wear unevenly.

As I said earlier tonight no seal will keep out all water all the time. Some will have a slower penetration but all will weep in time and once in the water won't come out (as there's very little pressure pushing the water out or it wouldn't have gone in much to begin with). Water will carry the dissolved and suspended grit or salts.

Some bearing designs are serviceable by complete disassembly or removal of seals to allow cleaning and relubing. Some aren't.

You need to find out what brand and model of Bb you have then ask more and/or search for servicing instructions. Andy.

If your current bottom bracket is a sealed cartridge, check for side-play with the arms attached. There should be zero to minimal side-to-side play in the arms. Then remove the arms and sin the axle with your fingers. There should be no binding, and it should turn smoothly without roughness. If either of these tests fail, consider replacing the cartridge.

If you have an open-ball type bottom bracket, the same tests apply, but if it fails either one, open it up and clean it out. Inspect the spindle and cups for wear (spindles generally show wear long before the cups). If just the spindle is worn, it can be replaced on its own. Replace all the balls, regardless. If both the spindle and cups are worn, consider replacing the whole bottom bracket with a sealed cartridge.

How long should they last? For me, 41 years to date for the 'unsealed' Sugino BB on my Gitane. Cups are still good. I had to replace the spindle a few years back because it just plain wore out. Balls have been replaced a few times. Yearly overhauls.

My Hollowtech II (Deore) bottom bracket lasted less than two years and just a few hundred miles. I guess time is worse for it that miles? The bike only got ridden in wet conditions a couple of times and never more than a mile, yet right now the bottom bracket is gooey and crunchy.

I tried to remove the seals to see if I could just overhaul each side but I damaged the seal on the left side so off to the LBS for a new BB.

Press fit bottom brackets like Trek's silly design don't last long.

Something is wrong with what you are doing. I have two BB-6700 (Ultegra) Hollowtech II bottom brackets installed in two bikes. One has 7000 and the other 6000 miles and both are in perfect operating order. Both bikes are ridden in mostly good weather but have been rained on and ridden hundreds of miles in the wet a fair number of times. They are not that fragile.

Posts #5 and 7 are great examples of why answers to questions like the OP posted are impossible to have a single one word answer. Hence my reply of two words, "it depends". Andy

It's very possible that I am over tightening the preload nut, which I've read reduces the life expectancy of the BB. I generally tighten it until there is no side-to-side play in the cranks. If it still feels really loose (like might easily unscrew and fall out) then I just slightly tighten it a little more. Usually, the point where the play is gone is close to as tight as I can get it with the little plastic tool.

I also found at least one online thread where numerous people had Deore BB's that lasted a ridiculously short period of time and then they installed an SLX or XT BB and it lasted a long time.

Also, I weigh 400 lbs so I put a lot of pressure on the bearings. I took one of them apart last night and I was shocked at how small the ball bearings were. I expected something closer to the outside diameter of the BB.

It's my understanding that many of the Shimano external BBs have used the same actual bearings and the differences between the "grades" are the housing cups and their weight/finishes. Andy.

That may indeed be correct. At least from UK suppliers, the cost difference between grades is very small, like $2 between 105 and Ultegra.

They are radial bearings and do no like side loads. Don't go over board on the adjusting nut.
The BB must be properly faced to get the most from the bearings.

Even from US suppliers a Dura-Ace level bottom bracket is only $30. Of course, bottom brackets, like hubs, are something that people buy Shimano for if they're happy with the low end/cheap stuff. For the record all my bikes have shimano hubs, and my road bike has a 105/Ultegra level BB, in case that statement offends!

What kind of bike, where's it been ridden, how's it been stored? Is there really water, sand in dirt in there or is it just a possibility the mechanic mentioned?

Four years old, it's probably some sort of cartridge bearing. If it's ridden on streets and stored inside, the BB's probably fine. If it's been regularly ridden through mudholes and stream crossings, then washed with a high pressure spray, it may be shot.

The best approach for a bottom bracket is to replace it when it really is shot. Test by trying to wiggle the cranks perpendicular to the plane of the bike frame. Even when the BB does break, you can ride it until you can get it to a bike shop to replace it. It'll sound like a Doritos commercial, but you'll still be able to pedal the bike.

the part of the frame BB Shell now comes in a vast variety of styles as well threaded types make replacing the Actual bearing assembly ever more rapid.


There were Zirk kits too grease goes in a tube between loose ball cups and adding more forced out the Old ..
WTB Grease guard went 1 up and puts a hole in the crank bolt, so that is a way the grease gets into the channel that leads to the internal route to do similar..

I built a touring frame in a shop near to the Burly tandem frame building and assembly shops so adopted their rear oversize cartridge bearing BB shell.

Butt (TIG) welded the 4 tubes to the outside of the shell and so the closed BB shell tube got a Zirk and the space between the bearings was filled with a good quantity of grease..

The bearing size I used are also used in automobile transmissions , like for Clutch throw out bearings..

No offense because I use the same components for the same reasons. However, given how well the "low end/cheap stuff" performs, it makes justifying the high end/expensive stuff a lot more difficult.

Agreed. I was on a group ride the other day when someone riding a very fancy bike commented on how lovely and quiet my rear hub was when I was coasting and asked me what brand it was. ;)

Ironic that you have to pay a lot more for a loud Chris King.

In my experience, sealed cartridge BB's easily last a decade.
External BB's have gone bad in as little as a year.

i've thrown away, for one reason or another, more good BBs than i've worn out. :)

The term "sealed" is a bit of a misnomer since the seals mostly keep the grease in but not necessarily the elements out...

I am resurrecting an old thread because it was one of the top hits when I asked Google how long a BB will last.

My Spec. Roubaix SL2 S-Works, 2009, has about 30,000 miles on the original BB. Mostly fair-weather Michigan riding with some rain and wet roads too. It was ridden for about 4 years, sat neglected in my garage for about 5 years, and has about 5,000 miles in the past two years. The original BB is still in it, has never been serviced, and has no lateral play and spins smoothly.

My 2008 Spec. Tarmac Pro was my race/training bike and has about 25,000 miles on it, same conditions as the Roubaix plus a few long wet races. Same storage, similar miles over the past two years as my friend has been riding it. The original BB is still in it, has never been serviced, and has no lateral play, spins smoothly.

Neither bike was ever pressure-washed, only garden hose and usually (always?) just water running over it, no nozzle nor stream from a finger over the hose.

There is a very significant difference in sealed bearing quality from different manufacturers and even between models from the same manufacturer. Enduro have made a name for themselves in the bicycle market but there are some other manufacturers doing similar quality work.

Had a Tange BB that went 35 years with nothing more than an occasional regreasing.

I've had Hollowtech "like" BBs that started ticking in less than 2 years.

(Crud- Forum glitch and I lost my long-winded reply.)

My rocket engineer friends unanimously agreed- don't touch the bearing until it indicates (noise, etc.) a need for service.

Modern bearings are marvels of engineering. Unlike the bearings many of old-timers remember, modern bearing seals don't leak, don't allow dust and other contaminants in, and the grease is good for 17,000 hours under industrial use. All under industrial loads of ~2,800 pounds of force and abusive test conditions.
As long as we don't directly spray the bearings with a pressure washer, a modern sealed bearing of good quality should a "lifetime" part. A low-quality bearing run under water and hit with 2,500 PSI water stream may be a monthly replacement.

Bearing design is precision science, well beyond my ability to understand. Here's a Google link if you want to see for yourself:

Ball and Roller Bearings NTN Americas

I can't post links yet so just Google it.

Your rocket engineer friends likely never worked in a bike shop and got to see real bike bearing life. We see rust and fine grit in every type of bike bearing routinely. Seals only reduce the size of grit to what can be "dissolved" in water and water will still get past most every seal given enough time and pressure. Like driving with your bike outside the car at 65mph in the rain for a few hours. Andy