# change bottom bracket



## saliva2002 (Jun 14, 2010)

my specialized came stock with a Shimano BB-ES25 bottom bracket, which i see now only cost $12 to the public, meaning the company paid 5 bucks. To me it feels like its not as smooth as it should be.... what would you recommend i replace it with... are all bottom brackets universal fit? I found the Shimano BB-UN53 for $27..... it costs more than 12 so i'm guessing its better? thanks for any input

heres the specs for my current BB: Shimano BB-ES25, Octalink spline, cartridge bearing, 68mm x 118mm


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## AndrwSwitch (Nov 8, 2007)

Bottom brackets are not universal.


saliva2002 said:


> heres the specs for my current BB: Shimano BB-ES25, Octalink spline, cartridge bearing, 68mm x 118mm


Octalink spline refers to the way the crank attaches to the bottom bracket. It's a hollow axle with eight splines. So the replacement you get needs to also be Octalink.

68mm refers to the width of the bottom bracket shell. You need to match that.

118mm refers to the length of the spindle. You don't necessarily need to match that, if you're trying to change the way your crank sits. But unless you're really clear on what you're doing, you should just get another 118mm spindle BB.

Finally, it needs to be English threaded.

If you take your chain off and turn your crank with your fingers, can you feel any grinding? If so, or if there's play that doesn't go away when you tighten the fixing bolts for the crank, you need a new bottom bracket. Otherwise, the grinding sensation is probably coming from someplace else.

If you go through with this project, you'll also need a crank puller and a special tool for removing and installing bottom brackets. I don't do it often enough to consider it worthwhile to own those, so for me it's a shop job. Clean your bottom bracket shell and grease the hell out of the threads. Can't remember if grease is indicated for octalink interfaces or not...


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## saliva2002 (Jun 14, 2010)

well when i bought it, it rode fine for a couple hours and then i felt popping in the pedals, every rotation at the exact same spot.... maybe not critical, but annoying as hell. I took it in and they basically told me that it wasn't doing that. i urged them it was and that i wasn't going to keep coming back so they took the whole bike apart and tightened the BB and it was gone. I can barely feel what i think is the popping coming back, but it could all be in my head now that i know it was there at one point and that it only cost Specialized $5 to buy it. So i'm hoping if i know i spent 30 instead of the 5 that they spent, it should be smoother and out of my head :madman: .... keyword: Hoping


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## AndrwSwitch (Nov 8, 2007)

The bearings in pedals are tiny, and if they're your stock pedals, they're also cheap and not very durable. I'd try to eliminate that as a cause before replacing the bottom bracket. Does it matter which chain ring you're using?

Did you check the crank for play, grinding or resistance yourself, or just run to the shop? If there's really a problem with the bottom bracket, you should be able to feel it when the chain is off. Note that a certain amount of resistance is normal, but it should be the same all the way around the rotation and it should feel smooth. Play would indicate a problem, but it could be either the bottom bracket itself being damaged, the bottom bracket being too loose, or the crank bolts being too loose.

Don't worry too much about what these things cost. Cartridge bottom brackets are a fairly simple, mass-produced item, in a location where the branding is invisible.

If you do replace it, don't get the UN-53. It uses a different standard in the way it attaches to the crank. You need an Octalink bottom bracket. I think that all Octalink V2 bottom brackets are coded ES-something.


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## zebrahum (Jun 29, 2005)

AndrwSwitch said:


> Can't remember if grease is indicated for octalink interfaces or not...


Yes it is; grease the spindle if it's round, no grease if it's square.


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## bbrins (Nov 2, 2009)

ah crap, wrong thread. sorry.


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## saliva2002 (Jun 14, 2010)

bbrins said:


> ah crap, wrong thread. sorry.


haha,,,, thanks for advice, it seems ok still, but if it starts the popping again i'll replace it. When it was doing it the first time I just ran to the bike shop (after I put a different set of pedals on, just in case) and they tightened it and it fixed the problem..... for now :eekster: and hopefully it stays fixed


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