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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 09-25-08, 07:16 PM   #1
nickdu
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How freely should the crank rotate?

I'm building a bike for the first time. Just got to putting on the crankset today. It's a deore xt m770. I'm wondering how freely should the crank rotate? There appears to be some friction (no noise, and it does rotate smoothly). If I spin it as hard as I can I can only get it to go around maybe 2.5 rotations (no chain attached). When I installed it it took some force to push the crank axle through the bottom bracket. Is that expected? Also, I can't easily pull it back out. I think I would need to bang on the axle from the left side with a mallot to get it back out.

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Nick
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Old 09-25-08, 07:24 PM   #2
BCRider
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If this in on a new BB then that's better than fine. You must be really winging it to get it to even go 2.5 turns. With the first 100 miles of riding it'll loosen up nicely and soon you'll find that if you tap a pedal much at all it'll zip around a couple of turns. The tightness of the seals when new and the grease being packed in the balls of the bearings all adds up and restricts how easily you can flip the cranks like this.

I've got a well broken in BB on a single speed that if I kick the pedal the cranks actually spin around about 5 or 6 times before stopping. When new it was worse then you have described.
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Old 09-25-08, 07:47 PM   #3
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A crank that spins freely multiple times needs grease in the bottom bracket.

Al
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Old 09-26-08, 05:17 AM   #4
nickdu
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Thanks, I feel better now. What about it taking force to push the axle through the bottom bracket and not being able to get it out easily? Is that the way it's supposed to work?

Thanks,
Nick
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Old 09-26-08, 08:28 AM   #5
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There is a device called a crank puller for removing cranks off a square taper.

Mallets are usually not necessary.
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Old 09-26-08, 10:34 AM   #6
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Quote:
Originally Posted by lymbzero View Post
There is a device called a crank puller for removing cranks off a square taper.

Mallets are usually not necessary.
It's a HollowTech BB and there's no square taper. He's talking about inserting the axle through the bearings. And some force is necessary due to the tight fit. Just lube the axle with some oil so it slides easier. Then apply steady pressure, no banging necessary. One way I've found to work well is just to lay the bike on its side with the BB-cup on a block of wood to keep it steady and vertical. Then push steadily down with my body weight. Use both hands to keep things even.
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