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Old 01-22-07, 03:10 PM   #1
squirtdad
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Bottom Bracket...Left hand thread

Hi,
I am trying to understand the lefthand thread bottom bracket cup thing.

I understand and take as fact that the fixed bottom bracket cup is left hand thread.

I understand why it is....except if the fixed bracket cup is on the right side of the bike and most pedaling is forward (pedals move in a clockwise circle), it would seem that the right side of the bike should right hand threaded and the left side bracket should be left hand threaded.

I have this wierd feeling I am missing some thing incredibly basic, but as am about to remove a very tight, right hand side fixed cup, I don't want to be making it tighter.......already I have found my first tool to use on the sheldon brown site.

thanks
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Old 01-22-07, 03:17 PM   #2
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What bottom bracket is it? I think there is a difference between English threaded BB and Italian threaded BB. Can you post that information?
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Old 01-22-07, 03:30 PM   #3
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Quote:
Originally Posted by squirtdad
Hi,
I am trying to understand the lefthand thread bottom bracket cup thing.

I understand and take as fact that the fixed bottom bracket cup is left hand thread.

I understand why it is....except if the fixed bracket cup is on the right side of the bike and most pedaling is forward (pedals move in a clockwise circle), it would seem that the right side of the bike should right hand threaded and the left side bracket should be left hand threaded.

I have this wierd feeling I am missing some thing incredibly basic, but as am about to remove a very tight, right hand side fixed cup, I don't want to be making it tighter.......already I have found my first tool to use on the sheldon brown site.

thanks
With English threaded bottom brackets, the left-hand thread on the drive side is to offset "precession." Here's a link to Sheldon's site regarding this, scroll down to "precession" and there are a couple of other links there as well: http://www.sheldonbrown.com/gloss_p.html#precession

And yes, if you've got a particularly stubborn bottom bracket cup to remove, the homeade tool Sheldon describes (a large bolt, nut, and washers combined with a socket wrench and a box-end wrench) does indeed work, although I had to add a hammer into the mix to finally loosen a very stuck fixed cup from a 1972 Raleigh International recently. I've removed quite a few bottom brackets, but nothing has come close, in my experience, to the degree of "stuckness" of this particular fixed cup. But sure enough, after a few days of soaking it in penetrating oil, and for good measure heating the shell up with a halogen worklight just before I began work with the wrenches, I finally gave a few good whacks with the hammer onto the end of the box-end wrench, and out she came-

Last edited by well biked; 01-22-07 at 05:41 PM.
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Old 01-22-07, 05:40 PM   #4
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Quote:
Originally Posted by squirtdad
I understand why it is....except if the fixed bracket cup is on the right side of the bike and most pedaling is forward (pedals move in a clockwise circle), it would seem that the right side of the bike should right hand threaded and the left side bracket should be left hand threaded.
Well, there's this: Pedaling turns the BB spindle toward the front. Between the spindle and the BB cup is a bearing. The spindle makes the bearing rotate the opposite way.
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Old 01-22-07, 05:44 PM   #5
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Quote:
Originally Posted by squirtdad
I am trying to understand the lefthand thread bottom bracket cup thing.
Easy answer: because when they used a right hand thread, the fixed cups tended to unscrew themselves!

Quote:
Originally Posted by squirtdad
I understand and take as fact that the fixed bottom bracket cup is left hand thread.

I understand why it is....except if the fixed bracket cup is on the right side of the bike and most pedaling is forward (pedals move in a clockwise circle), it would seem that the right side of the bike should right hand threaded and the left side bracket should be left hand threaded.
If you did that, both sides would tend to loosen spontaneously!

See: http://sheldonbrown.com/gloss_p.html#precession

Sheldon "Precession" Brown
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Old 01-22-07, 05:59 PM   #6
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Quote:
Originally Posted by well biked
With English threaded bottom brackets, the left-hand thread on the drive side is to offset "precession." Here's a link to Sheldon's site regarding this, scroll down to "precession" and there are a couple of other links there as well: http://www.sheldonbrown.com/gloss_p.html#precession

And yes, if you've got a particularly stubborn bottom bracket cup to remove, the homeade tool Sheldon describes (a large bolt, nut, and washers combined with a socket wrench and a box-end wrench) does indeed work, although I had to add a hammer into the mix to finally loosen a very stuck fixed cup from a 1972 Raleigh International recently. I've removed quite a few bottom brackets, but nothing has come close, in my experience, to the degree of "stuckness" of this particular fixed cup. But sure enough, after a few days of soaking it in penetrating oil, and for good measure heating the shell up with a halogen worklight just before I began work with the wrenches, I finally gave a few good whacks with the hammer onto the end of the box-end wrench, and out she came-
I had one that was super stuck. I put my bike in the training stand so that it was upright but solidly secured by the back axle. I inserted the Sheldon tool, then got a foot long length of pipe as a wrench handle extender. And then, very carefully, I stepped up on the end of the wrench to use my full body weight. It finally came loose.
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Old 01-22-07, 06:11 PM   #7
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Originally Posted by caloso
I had one that was super stuck. I put my bike in the training stand so that it was upright but solidly secured by the back axle. I inserted the Sheldon tool, then got a foot long length of pipe as a wrench handle extender. And then, very carefully, I stepped up on the end of the wrench to use my full body weight. It finally came loose.
Whatever works! On the one I described, I had tried using a pipe over the box-end wrench as a cheater bar, but still no-go (and I've gotten some very wickedly stuck items loose using that same pipe for automotive applications). The hammer blows I applied were apparently just the ticket in this case. But after hitting the wrench a few times, I was a bit concerned that something was going to give besides the bottom bracket cup, like maybe the nut would round over and then I'd really have a mess! And the Raleigh frame I was working on is a really nice one, so I was paranoid about a misplaced blow with the hammer as well. Luckily, everything came out okay-

Last edited by well biked; 01-22-07 at 06:31 PM.
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Old 01-22-07, 06:45 PM   #8
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OK.....so what I missed was precession, that is what I was curious about.

It is a an english BB (I assume it is an '82 Nnishiki) it had Sugino cranks..the cup itself has a kind of raised shelf/flat acrooss the face that looks like it needs a special wrench...therefore I will use the Sheldon Brown Universal BB Extraction tool...aks bolt, washers, nut, and sufficient leverage.

The adjustable cup came off really easily.....therefore the drive side is proving to be pain.....the old no such thing as a free lunch theory.

thanks all for the input
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Old 01-22-07, 08:30 PM   #9
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All my units have marks, like "L" and "R", I would look. I have seen some with an arrow pointing the direction of thread foreward.
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Old 01-22-07, 08:42 PM   #10
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Quote:
Originally Posted by squirtdad
.........the cup itself has a kind of raised shelf/flat across the face that looks like it needs a special wrench...

Here's where you can get the wrench you need for that type of fixed cup. A Park Tools PA-HCW11.

Pretty cheap at $14. If you plan to get one, don't dawdle. They're discontinued.

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Old 01-22-07, 10:16 PM   #11
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If you have a big vice you might try clamping the cup(by the flats) in the vice and then turning the bike clockwise.
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Old 02-01-07, 01:45 AM   #12
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I got the fixed cup off. Pretty low tech....even lower than the Sheldon Brown Magic Bolt.

I was looking in my tool mess....and found one of those stamped steel multi-tool.....probably circa 1974. Just out of curiosity I checked it and one of the slots fit.

I then used some threaded rod, nuts and washers to hold it tight against the bottom bracket. A few taps with a hammer (16 oz carpenters..... I'm already on a non appropriate tool approach) and it starts moving.

Key lessons a) using some method to hold the tool tight is a huge help and b) some times you just have to hit something with a hammer to loosen it up
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Old 02-01-07, 09:23 AM   #13
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Quote:
Originally Posted by Sheldon Brown
Easy answer: because when they used a right hand thread, the fixed cups tended to unscrew themselves!


If you did that, both sides would tend to loosen spontaneously!

See: http://sheldonbrown.com/gloss_p.html#precession

Sheldon "Precession" Brown
I'm having trouble visualizing this. A LH thread fixed cup loosens when turned to the right. The BB on the fixed cup side turns to the right during pedalling, so wouldn't the BB forces on the fixed cup tend to turn it to the right and loosen the fixed cup?
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Old 02-01-07, 11:10 AM   #14
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Quote:
Originally Posted by San Rensho
I'm having trouble visualizing this. A LH thread fixed cup loosens when turned to the right. The BB on the fixed cup side turns to the right during pedalling, so wouldn't the BB forces on the fixed cup tend to turn it to the right and loosen the fixed cup?
The precession effect turns the cups in the opposite direction of what you might suppose.

You can verify this by doing the pencil experiment described at:

http://sheldonbrown.com/gloss_p.html#pedal

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Old 02-01-07, 12:11 PM   #15
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Quote:
Originally Posted by San Rensho
I'm having trouble visualizing this. A LH thread fixed cup loosens when turned to the right. The BB on the fixed cup side turns to the right during pedalling, so wouldn't the BB forces on the fixed cup tend to turn it to the right and loosen the fixed cup?
The way I visulized it finally was like a set of gears. the axel (bb spindle ) moved forward (clockwise), but it rotates on the bearing, which then rotate backwards (counter clockwise). It is the bearings that exert force on the cup so even the the apparent (pedal direction) force is clockwise, the actual force (bearing) is counter clockwise...which would unscrew a right hand thread.
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Old 02-01-07, 12:18 PM   #16
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It's thought that the left-handed thread was innovated by Orville and Wilbur Wright in their Dayton bike shop. Pretty bright guys. I wonder what ever happened with them.
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Old 02-01-07, 12:25 PM   #17
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Quote:
Originally Posted by squirtdad
The way I visulized it finally was like a set of gears. the axel (bb spindle ) moved forward (clockwise), but it rotates on the bearing, which then rotate backwards (counter clockwise). It is the bearings that exert force on the cup so even the the apparent (pedal direction) force is clockwise, the actual force (bearing) is counter clockwise...which would unscrew a right hand thread.
But it's not like a set of gears because both the cups and the crank rotate on the same axis, unlike a set of gears. I won't claim to understand why precession happens though.

[edit] After trying the experiment on Sheldon's website, the "phenomenon" is most likely caused by the tiny clearances that exist in crank and pedal bearings (obviously cheaper BB's and pedals will thus suffer worse from this condition). If you actually hold the penicl tightly and try to rotate it, all the force is exerted in the same direction as it's applied. If you allow the pencil to wobble, that's when you get the force in the opposite direction. Anyone care to comment? [edit]

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Old 02-01-07, 12:56 PM   #18
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Quote:
Originally Posted by Sheldon Brown
The precession effect turns the cups in the opposite direction of what you might suppose.

You can verify this by doing the pencil experiment described at:

http://sheldonbrown.com/gloss_p.html#pedal

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|                                      --Anatole France   |
+---------------------------------------------------------+
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Old 02-01-07, 01:21 PM   #19
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Quote:
Originally Posted by squirtdad
The way I visulized it finally was like a set of gears. the axel (bb spindle ) moved forward (clockwise), but it rotates on the bearing, which then rotate backwards (counter clockwise). It is the bearings that exert force on the cup so even the the apparent (pedal direction) force is clockwise, the actual force (bearing) is counter clockwise...which would unscrew a right hand thread.
This is a common, but incorrect explanation. The bearing balls apply no rotary force other than friction, since they are not anchored to anything.

The precession effect results from the fact that the male thread (cup or mounting ring) must always be ever-so-slightly smaller than the female thread (bb shell) it fits into, so the cup rolls around within the thread, unless it is tight enough to make it truly immobile.

Sheldon "Precession" Brown
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Old 02-01-07, 01:30 PM   #20
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Quote:
Originally Posted by Sheldon Brown
This is a common, but incorrect explanation. The bearing balls apply no rotary force other than friction, since they are not anchored to anything.

The precession effect results from the fact that the male thread (cup or mounting ring) must always be ever-so-slightly smaller than the female thread (bb shell) it fits into, so the cup rolls around within the thread, unless it is tight enough to make it truly immobile.

Sheldon "Precession" Brown
Correct. It's the "walking thread" syndrome.
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Old 02-01-07, 03:34 PM   #21
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Quote:
Originally Posted by Sheldon Brown
This is a common, but incorrect explanation. The bearing balls apply no rotary force other than friction, since they are not anchored to anything.

The precession effect results from the fact that the male thread (cup or mounting ring) must always be ever-so-slightly smaller than the female thread (bb shell) it fits into, so the cup rolls around within the thread, unless it is tight enough to make it truly immobile.

Sheldon "Precession" Brown
I stand educated....and my fixed cup is out! Interesting how much phyiscs and engineering are in a "simple" bike!
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