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Old 01-18-07, 08:26 PM   #1
kmart
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How can I tell if my BB is smooth?

I just got a frame with a bottom bracket which I think is fairly new, but I am not sure. When I turn the BB spindle by hand there is no grinding or stepped motion, so that's good. My main question is, should the spindle rotate freely for a few turns if I start it spinning by hand? It might not do it because it is packed full of grease, or it might be that it is too tight, so I really don't know.
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Old 01-18-07, 08:38 PM   #2
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Not all bottom brackets are built the same. BB with cartridge bearings will typicaly allow your cranks to spin many times without slowing. With loose bearings (cup and cone style) you're lucky to get 2 full rotations before it stops.

As long as the motion is smooth with no grinding or stepping motion as you said, and the cranks arms aren't wobbling, you're golden. Don't worry about how much the cranks spin.
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Old 01-18-07, 08:42 PM   #3
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Originally Posted by atomsuite
As long as the motion is smooth with no grinding or stepping motion as you said, and the cranks arms aren't wobbling, you're golden. Don't worry about how much the cranks spin.
Exactly. Cartridge bearings typically are very SMOOTH, but slightly higher resistance than loose bearings. So a loose bearing BB will spin longer, even though it won't be quite as smooth.

You want your bearings to be smooth and have ZERO play (wobble). How long they spin for is not generally important. Besides, it's very hard to get a bottom bracket spinning because it has such a small moment of inertia (the mass is all close to the axis of rotation). If you attach a crank arm to it you'll be able to spin it much harder
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Old 01-18-07, 11:03 PM   #4
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Quote:
Originally Posted by atomsuite
BB with cartridge bearings will typicaly allow your cranks to spin many times without slowing. With loose bearings (cup and cone style) you're lucky to get 2 full rotations before it stops.
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Originally Posted by moxfyre
Exactly. Cartridge bearings typically are very SMOOTH, but slightly higher resistance than loose bearings. So a loose bearing BB will spin longer, even though it won't be quite as smooth.
thats great, you guys agree on exactly opposite statements..

Loose balls, set up properly, should offer less resistance, or be "smoother", than sealed cartridge type bearings.
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Old 01-18-07, 11:33 PM   #5
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Quote:
Originally Posted by mcoine
thats great, you guys agree on exactly opposite statements..

Loose balls, set up properly, should offer less resistance, or be "smoother", than sealed cartridge type bearings.
not exactly, they both agreed on the main point which is that it doesn't matter how many times your bb spins w/out the crankarms on, instead it matters that it revolves smoothly.
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Old 01-18-07, 11:48 PM   #6
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If you don't have a bike repair stand it would be difficult for you to assess accurately .
It needs to be clamped in the repair stand with the cranks installed.
Grab both cranks and see if you can detect any play. If not, and you can feel no roughness, it's ok.
If there's a teeny bit of play but it turns smoothly there's some life left in it.
More than a teeny bit of play or roughness, replace it.
If you take a brand new cartridge bottom bracket out of the box and spin the spindle with your fingers there is a surprising amount of resistance. That's normal. If it spins super easy then I would say that it is an indication of wear.
It is a good idea, before you install the cranks, to check the tightness of the cups.
If you don't have the tools have them check them at the bike store. Take the cranks with you and ask them to check the condition of the bottom bracket as well.
If it's no good, have them replace it.
I'm assuming you have a cartridge bottom bracket.
If you don't have a cartridge BB and you are not familiar with them take it to a bike shop.
There's a lot of variation in the adjustment hardware used.
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Old 01-19-07, 06:34 AM   #7
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Quote:
Originally Posted by mcoine
thats great, you guys agree on exactly opposite statements..

Loose balls, set up properly, should offer less resistance, or be "smoother", than sealed cartridge type bearings.
Yeah, that's kind of funny I'm pretty darn sure that every properly adjusted loose ball BB I've worked on has had less resistance than a cartridge BB.

In any case, the point is that a BB should turn smoothly, with little resistance, and ZERO play.
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Old 01-19-07, 07:19 AM   #8
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Quote:
Originally Posted by moxfyre
Yeah, that's kind of funny I'm pretty darn sure that every properly adjusted loose ball BB I've worked on has had less resistance than a cartridge BB.

In any case, the point is that a BB should turn smoothly, with little resistance, and ZERO play.
Generally speaking, you are correct. Loose ball bearings have less resistance than cartridge. However, my girlfriends bike has an Ultegra 9 cartridge BB that will spin for a day and a half. It is amazing. When connected to a the rest of the drive train (Ultegra chain and DA 7700 hub) it will still spin about 10 times before it stops (53-19ish gears). The whole setup is some kind of miracle! I will spin the pedals backwards on it sometimes when I walk by.

I want to take it on a good group ride sometime and see how little I have to pedal in a good solid draft, as we are the same height, so it fits. The Terry Butterfly is a bit of an embarassement.
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