Shimano cartridge BB question

[Mikeyankee]

Just installed a new BBUN-73 and was curious about the black ring (appears to be anodized aluminum)
pressed on to the drive-side spindle just inside of the tapers, which was not on the previous
BBUN-72 model. Anybody know its purpose?

Mike Yankee

(Address is munged to thwart spammers. To reply, delete everything after "com".)

 

[Meccanico Di Bi]

[email protected] (MikeYankee) wrote in message
news:<[email protected]>...
> Just installed a new BBUN-73 and was curious about the black ring (appears to be anodized
> aluminum) pressed on to the drive-side spindle just inside of the tapers, which was not on the
> previous BBUN-72 model. Anybody know its purpose?
>
>
> Mike Yankee
>
> (Address is munged to thwart spammers. To reply, delete everything after "com".)

It's to keep gorilla taper-greasers from gunning on their cranks 'til they hit the cup or blow the
crank arm up. What I find amusing is those bb's come with a little white grease on the tapers,
inviting the crank to go on too far. I'll usually tap the ring off with a punch and whipe off the
grease. Cheers. --Jim

 

[Peter Headland]

> It's to keep gorilla taper-greasers from gunning on their cranks 'til they hit the cup or blow the
> crank arm up. What I find amusing is those bb's come with a little white grease on the tapers,
> inviting the crank to go on too far.

What I find amusing is the frequency with which nonsense like this is posted here, despite people
who actually know what they are talking about having dispelled this myth many years ago.

 

[Sheldon Brown]

MikeYankee wrote:
> My question was, what's the black ring for? And why is it on the right side only?
>
> There's gotta be a reason, because it wasn't on the previous generation of cartridge BB's and
> adding it entails both weight and cost.

Shimano calls this a "chain line stabilizer" or something like that. It's to keep the crank from
getting driven on too far by overenthusiastic tightening.

Sheldon "The Left Should Be Tighter Than The Right, Even Though The Right Is Easier To Tighten"
Brown +--------------------------------+
| One does not win at chess by | seizing every opportune pawn | -- Michael Flynn |
+--------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone 617-244-9772 FAX
617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide http://captainbike.com
http://sheldonbrown.com

 

[Gary Young]

[email protected] (Peter Headland) wrote:

<snip>
> Since it is on one side only, it obviously is nothing to do with preventing the crank moving too
> far up the spindle. If the ring is fairly large, I would guess it is there to stop a dropped chain
> getting trapped between the crank and the BB? If it is small, I have no idea of its purpose.

It's only on the right side that moving the crank too far up the spindle will risk damage to the
chainstays from the chainrings. Doesn't it make sense that it's designed to prevent that? (It's
small, by the way -- probably only three or four mm's bigger in diameter than the spindle.)

 

[Peter Headland]

> Shimano calls this a "chain line stabilizer" or something like that. It's to keep the crank from
> getting driven on too far by overenthusiastic tightening.

That doesn't make sense. Surely, if the little ring in question is a press fit on the crank, anyone
who is tightening the crank bolt enough to drive the crank all the way up the taper would be able to
displace the ring with little additional effort? Or is there a shoulder on the axle to prevent that?
Or are people supposed simply to see when crank meets ring and quit whaling on the bolt?

 

[Peter Headland]

> It's only on the right side that moving the crank too far up the spindle will risk damage to the
> chainstays from the chainrings. Doesn't it make sense that it's designed to prevent that?

Good point - I was thinking about "stretching" the crank, not ramming the chainring into the stay.
Either way, isn't it frightening to think that people would actually do that?

The major cause of cranks being pushed too far up the axle is supposed to be people thinking that
you have to keep the crank bolt really tight all the time. Since the crank naturally creeps up the
axle a tiny bit under load, that bolt is never so tight as when you first install the crank.
Constantly retightening the bolt is like working a ratchet - the crank keeps creeping up the axle
away from the bolt even though you never apply enough force to the bolt to get it there from
scratch. The little collar on the axle would be enough to prevent that ratchet effect (by stopping
the crank from creeping), so long as you only tighten the bolt to a reasonable approximation to the
recommended torque (otherwise you'd move the collar with the crank).

But I am left with this puzzle - if Shimano have decided that people who abuse their cranks in this
way should be saved from themselves, why not put the collars on both sides? OK, you won't run a ring
into the stays on the other side, but you will wreck the crank, which could be dangerous.

 

[Ed Chait]

"Sheldon Brown" <[email protected]> wrote in message
news:[email protected]...

> Sheldon "The Left Should Be Tighter Than The Right, Even Though The Right Is Easier To
> Tighten" Brown

Just curious, why is the right easier to tighten?

Ed Chait

 

[Chris B .]

On Wed, 02 Jul 2003 05:14:09 GMT, "Ed Chait" <[email protected]> wrote:

>
>"Sheldon Brown" <[email protected]> wrote in message
>news:[email protected]...
>
>> Sheldon "The Left Should Be Tighter Than The Right, Even Though The Right Is Easier To
>> Tighten" Brown
>
>
>Just curious, why is the right easier to tighten?
>
>Ed Chait

I was wondering about this too. I suspect that Sheldon holds the right crank against the chainstay
with his left hand while tightening the right crank bolt. On the left side, the crank is going to be
pointing forwards in free air when the left crank bolt is being tightened. I often tighten the left
side by aligning the *wrench* with the chainstay and pushing down on the pedal, sometimes while
standing on the right side of the bike and leaning over it.

Chris Bird

 

[Meccanico Di Bi]

[email protected] (Gary Young) wrote in message
news:<[email protected]>...
> [email protected] (Peter Headland) wrote:
>
> <snip>
> > Since it is on one side only, it obviously is nothing to do with preventing the crank moving too
> > far up the spindle. If the ring is fairly large, I would guess it is there to stop a dropped
> > chain getting trapped between the crank and the BB? If it is small, I have no idea of its
> > purpose.
>
> It's only on the right side that moving the crank too far up the spindle will risk damage to the
> chainstays from the chainrings. Doesn't it make sense that it's designed to prevent that? (It's
> small, by the way -- probably only three or four mm's bigger in diameter than the spindle.)

I think Shimano is less interested in a frame being damaged from the chainrings as they are the
chainline. Shimano front der's won't work unless the chainrings are a certain distance away from the
centerline of the frame. I think for a triple on a traditional 28.6mm seat tube, it's supposed to be
47-50mm from frame center to the center of the middle chainring. If Mr. Gorilla taper-greaser guns
the crank on too far, and doesn't kill the crank, the front der. will collapse fully onto itself and
hit the seat tube before it can knock the chain off the middle ring into the small ring. This is
even more common on frames with "oversize" 31.8 & 34.9mm seat tubes. It's rarely a problem on 28.6mm
tubed frames. This is why Shimano has two widths of most bottom brackets, fat seat tube frames need
longer spindles so the front der's will work.

We often find that old cranks whos square hole has been a bit opened-up over the years will bottom
out on those newer bbs with the collar well before adequate torque has been applied, forcing the
removal of said collar. --Jim

 

[Ed Chait]

"Chris B." <[email protected]> wrote in message
news:[email protected]...
> On Wed, 02 Jul 2003 05:14:09 GMT, "Ed Chait" <[email protected]> wrote:
>
> >
> >"Sheldon Brown" <[email protected]> wrote in message
> >news:[email protected]...
> >
> >> Sheldon "The Left Should Be Tighter Than The Right, Even Though The Right Is Easier To Tighten"
> >> Brown
> >
> >
> >Just curious, why is the right easier to tighten?
> >
> >Ed Chait
>
> I was wondering about this too. I suspect that Sheldon holds the right crank against the chainstay
> with his left hand while tightening the right crank bolt. On the left side, the crank is going to
> be pointing forwards in free air when the left crank bolt is being tightened. I often tighten the
> left side by aligning the *wrench* with the chainstay and pushing down on the pedal, sometimes
> while standing on the right side of the bike and leaning over it.
>
> Chris Bird

I just go to the left side of the bike, hold the left crank and chainstay with my left hand,
and tighten in the same manner I do the right. Still don't understand why the right side would
be easier.

Ed Chait

 

[Dianne_1234]

[email protected] (MikeYankee) wrote in message
news:<[email protected]>...
> Just installed a new BBUN-73 and was curious about the black ring (appears to be anodized
> aluminum) pressed on to the drive-side spindle just inside of the tapers, which was not on the
> previous BBUN-72 model. Anybody know its purpose?

It's to stop the air-driven socket wrenches spoiling the chainline during crank installation on a
mass-production assembly line.

 

[Mike S.]

> > >"Sheldon Brown" <[email protected]> wrote in message
> > >news:[email protected]...
> > >
> > >> Sheldon "The Left Should Be Tighter Than The Right, Even Though The Right Is Easier To
> > >> Tighten" Brown
> > >
> > >
> > >Just curious, why is the right easier to tighten?
> > >
> > >Ed Chait
> >
> > I was wondering about this too. I suspect that Sheldon holds the right crank against the
> > chainstay with his left hand while tightening the right crank bolt. On the left side, the crank
> > is going to be pointing forwards in free air when the left crank bolt is being tightened. I
> > often tighten the left side by aligning the *wrench* with the chainstay and pushing down on the
> > pedal, sometimes while standing on the right side of the bike and leaning over it.
> >
> > Chris Bird
>
> I just go to the left side of the bike, hold the left crank and chainstay with my left hand,
> and tighten in the same manner I do the right. Still don't understand why the right side would
> be easier.
>
> Ed Chait
>
>
I usually grab the crankarm at say 7-8 o'clock and put the wrench at 4-5 o'clock and tighten towards
6 o'clock. That way, if something slips, I don't have chainrings gouging my hands...

I can tell you from experience that chainring teeth don't tickle!

Mike

 

[Sheldon Brown]

Chris B. wrote:
> On Wed, 02 Jul 2003 05:14:09 GMT, "Ed Chait" <[email protected]> wrote:

I signed:

>>>Sheldon "The Left Should Be Tighter Than The Right, Even Though The Right Is Easier To
>>>Tighten" Brown

Ed Chait asked:

>>Just curious, why is the right easier to tighten?

Chris Bird theorized:

> I was wondering about this too. I suspect that Sheldon holds the right crank against the chainstay
> with his left hand while tightening the right crank bolt. On the left side, the crank is going to
> be pointing forwards in free air when the left crank bolt is being tightened. I often tighten the
> left side by aligning the *wrench* with the chainstay and pushing down on the pedal, sometimes
> while standing on the right side of the bike and leaning over it.

Actually, no.

I generally rotate the bike in the workstand so the front is pointing straight up at the or maybe a
bit higher, so that the bottom bracket is a little higher than my belly button.

Here's how I tighten the left side: With the right crank facing downward, and my trusty 18"
Craftsman half-inch drive ratchet also facing downward, I jerk on the ratchet handle directly toward
me while holding the right crank with my left hand. Sometimes I'll have my left hand wrapped around
both the right crank and chainstay. My ratchet handle is considerably longer than the crank, so the
crank itself is the limiting factor to how hard I can get it.

Note that I don't have a lot of upper body strength, so for the left side I pretty much give it
everything I've got. Stronger folks might need to be more restrained.

For tightening the right side, I don't actually need to hold the crank, I just grab the tire, and
the bike's gearing lets me easily resist any amount of torque I could apply with the wrench.

Sheldon "My Way" Brown +-------------------------------------------------+
| What is good for you is what is good for you. | --Peter Chisholm |
+-------------------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone
617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com