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Thread: Bottom Brackets

  1. #1
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    Bottom Brackets

    Hi guys!

    Does anyone know about bottom bracket tech? I'm really kind of lost. Been sifting through other threads on the forum, and other bits of info here and there, but still can't really catch it.

    Anyway, i'm riding a 2008 trek fuel ex 6 that uses an octalink. Is there anyone who uses the same/ similar setup out there? i'd like to know more about my BB options. Thinking of swapping it out.

  2. #2
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    Why do you want to swap it? Bottom brackets don't usually need to be replaced, and there's really not much to be gained by changing it just because.

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    If you trash an Octalink BB, you need another Octalink BB. Match the spindle length and shell width.

    Shimano uses higher numbers on nicer parts. Not sure which Octalink models they're currently manufacturing, since they've moved on with their current-model stuff. But you should have no trouble finding one, they are still making them as a maintenance part.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

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    Thanks for the responses so far guys. Just thinking of some alternatives and options 'cause that octalink has been in use pretty intensively for about 4 years. Don't really want to wait for a problem to occur while i'm on the trail.

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    Just echoing what has been said above... "If it ain't broke, don't fix it" so to speak.

    But, if you really feel you have to replace it, you'll need a crank puller, BB socket, grease, a big adjustable wrench and a torque wrench. And of course a new bottom bracket. Just Google "Octalink bottom bracket" and you'll find a variety of options for the part, and then read the walk through on the Park Tools page and you should have no problem with replacing it, it's really quite simple.
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  6. #6
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    Quote Originally Posted by romeslipslide View Post
    Hi guys!

    Does anyone know about bottom bracket tech? I'm really kind of lost. Been sifting through other threads on the forum, and other bits of info here and there, but still can't really catch it.

    Anyway, i'm riding a 2008 trek fuel ex 6 that uses an octalink. Is there anyone who uses the same/ similar setup out there? i'd like to know more about my BB options. Thinking of swapping it out.
    Basically there are two types of BBs

    Internal and External

    Internal ones (like Octalink or ISIS) have the bearings inside the bike frame...

    External ones have cups that screw into the frame and the bearings are bigger and outside the frame.

    Octalink, Isis, and square taper refer to the spline that connects the crank arms to the crank shaft...of course your cranks have to fit the axled shaft....

    Most find that the external bearing types have bigger bearings and better seals that last longer, than the internal types.....

    I have found this to be the case as well.....even the old square taper cranks with cup and cone bearings wear out faster than a good external BB....

    So if you want to get away from Octalink you will need to buy a BB and cranks to match...

    Octalink is however a pretty good BB set-up....

    Unless you are riding lots of creeks and perhaps snowy walty winters....

    Components > Drivetrain > Bottom Brackets | Jenson USA Online Bike Shop

  7. #7
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    Quote Originally Posted by romeslipslide View Post
    Thanks for the responses so far guys. Just thinking of some alternatives and options 'cause that octalink has been in use pretty intensively for about 4 years. Don't really want to wait for a problem to occur while i'm on the trail.
    I have one that's over ten years old.

    It's very unlikely to fail catastrophically. Most internal bottom brackets let you know they're worn out by developing play or getting gritty. I check mine by seeing if I can feel play pushing the crank arm toward or away from the frame. Then I rotate it 90 degrees and try again. To get a feel for the smoothness of the bearing surfaces, derail your chain and let it fall to the inside of the crank. Or wherever - just out of the way. Then rotate the crank with your fingers. Hold it right near the crank bolt.

    No play, no grinding? Awesome. Recheck it when you change your chain - it's an easy time to do it, and fairly good as a checkup interval for things that wear slowly.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

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    Quote Originally Posted by jeffscott View Post
    Basically there are two types of BBs

    Internal and External

    Internal ones (like Octalink or ISIS) have the bearings inside the bike frame...

    External ones have cups that screw into the frame and the bearings are bigger and outside the frame.

    Octalink, Isis, and square taper refer to the spline that connects the crank arms to the crank shaft...of course your cranks have to fit the axled shaft....

    Most find that the external bearing types have bigger bearings and better seals that last longer, than the internal types.....

    I have found this to be the case as well.....even the old square taper cranks with cup and cone bearings wear out faster than a good external BB....

    So if you want to get away from Octalink you will need to buy a BB and cranks to match...

    Octalink is however a pretty good BB set-up....

    Unless you are riding lots of creeks and perhaps snowy walty winters....

    Components > Drivetrain > Bottom Brackets | Jenson USA Online Bike Shop

    Hi man thanks. This really helped me understand a bit more about BBs. Thing is, I've got quite a bit of mud and wet bits where I'm riding. Very tropical, so bike components tend to wear a little faster.

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    Quote Originally Posted by AndrwSwitch View Post
    I have one that's over ten years old.

    It's very unlikely to fail catastrophically. Most internal bottom brackets let you know they're worn out by developing play or getting gritty. I check mine by seeing if I can feel play pushing the crank arm toward or away from the frame. Then I rotate it 90 degrees and try again. To get a feel for the smoothness of the bearing surfaces, derail your chain and let it fall to the inside of the crank. Or wherever - just out of the way. Then rotate the crank with your fingers. Hold it right near the crank bolt.

    No play, no grinding? Awesome. Recheck it when you change your chain - it's an easy time to do it, and fairly good as a checkup interval for things that wear slowly.
    Thanks! this is good. So basically, if i'm feeling huge amounts of grit, i'm in trouble?

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    Quote Originally Posted by romeslipslide View Post
    Thanks! this is good. So basically, if i'm feeling huge amounts of grit, i'm in trouble?
    Even with a lot of grit, your bike won't be dangerous to ride. Like someone said, catastrophic BB failures are rare. It's one of those components that you don't necessarily ignore, but it's not like it's on the forefront of your mind all the time. If you want to replace the BB, you might wait until your chainrings are worn out and replace the entire crankset.

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    Quote Originally Posted by s0ckeyeus View Post
    Even with a lot of grit, your bike won't be dangerous to ride. Like someone said, catastrophic BB failures are rare.
    Sorry not really true....

    Happened to me...

    You have a slightly gritty BB, so you go on a ride....up 2000 vert ft then down the other side.....about 25 km....

    Only way back is up 2000 vert ft the down the front side....

    The thing just got heavier and heavier to pedal....

    By the time I got out I was damn near done and we were 3 hours longer....

    Nope change it when it gets gritty.


    BTW ever since that ride I have had a Shimano XT external BB and crank set....

    When the bearings die on it the get loose and sloppy....The FD doesn't shift great....but you can still pedal fine.

  12. #12
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    Quote Originally Posted by romeslipslide View Post
    Hi man thanks. This really helped me understand a bit more about BBs. Thing is, I've got quite a bit of mud and wet bits where I'm riding. Very tropical, so bike components tend to wear a little faster.
    Well I got some mud but ride a long cold salty winter...also hard on the drive train....

    Sounds to me like an external cup bearing set up is what you are looking for sooner or later...

    Shimano stock bearings are okay.....but they have some stainless steel (Phil woods I think) bearings...

    Also ceramic hybrids from Enduro also last well, had have a much better seal...

    Anyway it all costs money.

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    I just pulled the sealed cartridge square taper BB out of an old dirtbag I recently got and am now overhauling. Play in a BB is something I wouldn't ignore. A little grit developed on my GXP external BB that is on my Range some time ago and is felt when thrown in the stand. But with that BB, that isn't unheard of and it disappears on the trail. With a sealed cartridge BB, they're so cheap you may as well pull it and replace it for your own good. It's like neglecting the manufacturer's label that says you need to replace the powerlock each time you break a sram chain off your bike. Go ahead, but its your safety and your bike. I've only broken one BB shell, but it still isn't any fun. No play and no grit, leave it be.

    Use thicker grease if it isn't getting cold out there. Anything light like slick honey will seemingly evaporate. Understanding bearing grades isn't very hard, but primarily you're going to want a strong seal. Some great ceramic bearings in a BB will come terribly sealed and need maintenance more often. If you've got a cartridge sealed BB, you won't really be servicing it. I wouldn't drop real money on a BB. I've subscribed to some silly BS on a bike build, but not overpriced BBs. Maybe if I was sponsored and got thrown them like dog treats. Nothing really wrong with stainless bearings, they've done the job for many alike. It's all relative to your paycheck in the end.

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