MatthewJRudd

So I had my bike in for a tune-up last week, and the mech let me know that the BB was pitted and was going to need replacing soon (~1000km). Since the part ordering was going to add another week to my off-bike time (I know, I need a backup), not to mention I was already installing a new chain and cassette, I passed.

My question is: how do I know when it actually needs replacing? Furthermore, is running a pitted BB going to cause any knock-on damage to any of my other components? Is there a sound I should be looking out for, or will I just notice a degradation in performance? I have a LBS which doesn't need to order the part, am I better off just picking it up and doing the install now?

Thanks for your wisdom.

pdlamb

Pitted BB; that's a very, interesting? claim.


Grab your cranks, and then try to wiggle them perpendicular to the long axis of the bike. If they move back and forth, you need a new BB.


There's no rush to change the BB until they exhibit wear, as found by the wiggle test. Since modern bottom brackets include bearings, races, and the center shaft, there's nothing they can affect as they wear. If yours is actually worn out at 1,000 km, that's a new low record that I've heard of.

HillRider

How old is the bike? What type of bottom bracket? How did the mechanic know it was pitted, did he disassemble it completely?

As pdlamb noted 1000 km has to be a new speed record for replacement unless the bike was immersed in salt water all the time.

Andrew R Stewart 

Well given the hugs number of really worn out BBs I've seen and that I see them often when the bike is brought into the shop for some other reason I would suggest that replacement time is totally subjective. We get so bound up in "standards" and "guidelines" when what really maters is the rider's perceptions and tolerances. Until the worn out parts cause other issues (like the crank/rings rock back and forth to a degree that this movement causes the chain to derail) worn parts can continue to wear yet "work".


I find the best way to gage bearing wear in general is to remove any levers involved then spin the bearing by hand and feel it's smoothness, or roughness. For a Bb this means removing the crank arms and turning the Bb spindle with your fingers. It's surprising how different a bearing will seem when spun by the end of the crank arm (or rim) compared to just the axle being rotated.


But in the end without X Ray eyes actual bearing track/balls conditions is unknown without taking all apart. I suspect the shop merely spun the crank, maybe even without removing the chain from the rings, say the rotation was not smooth and assumed that the ball tracks were pitted. This is a common quickie to do an initial assessment. Most all shops do this. And most shops have found that actual taking apart gives the real, no assumptions, answers.


BB, or any other bearing, wear is not solely a mileage thing. The initial set up, follow up maintenance, the load when riding, the conditions (rain, salted streets, mud) are all more important as the grade of the bearings, IMO. This is why one rider gets 10,000 miles+ before the need to replace and another rider gets less then 1000 miles. Andy.

corrado33

No one, that I know of, takes apart sealed BBs.

They're too cheap not to replace.

My guess is they spun the cranks, either felt or heard roughness/looseness and said the BB will need replaced relatively soon. They're probably not wrong.

EDIT: As for the OP. There is almost nothing you can damage by using a worn out SEALED BB. It'll just affect your ride quality. Ride it till it falls apart if that's your desire. Or, fix it. They're only $20 or so for good BBs that'll probably last 1000s of miles.

Dave Mayer

I was wrenching at the shop yesterday, and someone came in with a mangled front derailleur.

Further diagnosis indicated a worn-out BB, specifically a pitted spindle. So the wonky BB had produced enough play in the crankset so that the chain or big ring had caught and twisted the front derailleur.

We replaced the FD, the BB spindle, and installed 22 new 1/4" balls. Total parts cost: $30; 60 minutes of labor.

FBinNY 

There's a decent chance the BBC will outlast you, especially if you can accept some roughness in the cranks.

In use the balls maintain the surface they roll on, the same way passing trains keep tracks polished despite being out in the weather. Eventually the balls will wear through the hard surface layer of the races and cause them to break down, at which point wear will get much faster.

It's possible that you've reached that point and that's what the mechanic meant by "pitted". So plan on buying a spare soon, just in case, but odds are that even in the worst case, you still have some time.

Andrew R Stewart 

Andy

MatthewJRudd

Thanks guys for the feedback. The bike is a 2012 Madone, but it's new to me so I have no idea how old the BB is. Best guess it's original. I'll probably pick up a new one on my next cheque, but it's good to know that I'm not likely to hurt anything else by riding it a bit too long.

Oh, and if I wasn't clear, the mechanic was saying that the BB had 1000km left in it, not that it was going to go after only 1000km. I'm a newbie but even I would have found that a mite suspicious.

rm -rf

Your bike has cartridge bearings, which are replaceable, usually by buying a new bottom bracket. (I don't have experience with the older loose ball bottom brackets.)

If I suspect my bearings are getting rough, I'll take the chain off the crank (I use quick links to join the chain, so it's easy.) Then spin the crank without the chain to see that it spins fairly freely (it won't spin a long time like a wheel does).

If I then suspect worn bearings, I'll pull the crank off and use my fingers to turn each side's bearings by hand. I can feel if one or both are rough.

(Your mechanic can tell when it's "1000 km" from needing replacement? Huh.)

scott967

Seems like this would be BB86? My experience with PF30 is that they don't last long. I would just get a new BB and replace. I would spend a few bucks and get something like the Wheels Manufacturing "screw-together" BB which I think is much better than the press-in plastic cups.

scott s.
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