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Threadless BB Cartridges: Why/Why Not?



 
 
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  #11  
Old February 25th 06, 10:12 PM posted to rec.bicycles.tech
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Default Threadless BB Cartridges: Why/Why Not?

Tom Sherman writes:

Thanks to Werehatrack for introducing me to the concept...
Now it begs the question:
Why are BB shells threaded in the first place?
i.e. Why don't most bikes just come with threadless
already installed?
Sounds like there's a downside...


I must have missed it but could you direct me to a web site where I
can see the cross section of a threadless BB? The only ones I know
of were on Ashtabula cranks and they had a larger diameter.


Surely, you recall the Mavic system of the eigties? Conical rings on
both sides screw onto a threaded Phil-ish cartridge. IN Mavic's
design, the frame gets milled with a 4mm chamfer on each end of the
BB. The later all-nylon-casing types (KSS brand) seem to work fine
without that chamfer.


I don't recall, and don't call me Shirley.


They are both more expensive to make and much more time consuming to
install. As such they can't be an OEM part and in today's world
that is a kiss of death. Low volume means high prices which leads
to low volume and therefore high prices, etc.


Picture reference please. I don't have much hope though because these
folks seldom show a cross section drawing where the function is
revealed. You might suspect they don't trust their patent protection.


Is this the referenced BB? See


http://www.bikepro.com/products/bott...ets/mavic.html

Insterding! Just the outer picture leaves me wondering what else they
didn't test. At least the text explains what the intent was. In this
design, the tube pictured is centered on threads that Mavic hoped
would be radially clearance free, unlike standard BB cups. I don't
believe that is a reasonable supposition unless the conical rings had
at least two splits to allow them to clamp, as my pedal attachments
do.

What's worse is that there is no explanation of how the spindle is
secured in the bearings and what sort of bearings these are.

Just to give an idea of the fragility of BB retention, I recently had
the right hand cup loosen and not be tightenable. When I removed it,
I discovered that more than 100000 miles of riding had eroded the
threads from the steel BB shell. The right side thread was completely
gone and the left side close behind. The right hand cup had been
brutally tightened and never removed during that time. Fretting
gradually ate up the threads leaving nothing but grey paste.

My frame maker bored the BB shell and silver soldered in steel
threaded sleeves abut 12mm deep on either side.

It is from this sort of experiences that I am suspicious of the
Shimano over-hung BB bearing design. How can that work even nearly as
well as internal BB cups?

Jobst Brandt
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  #12  
Old February 25th 06, 10:38 PM posted to rec.bicycles.tech
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Default Threadless BB Cartridges: Why/Why Not?

On Fri, 24 Feb 2006 14:03:24 -0500, "(PeteCresswell)"
wrote:

Thanks to Werehatrack for introducing me to the concept...

Now it begs the question:
Why are BB shells threaded in the first place?
i.e. Why don't most bikes just come with threadless
already installed?

Sounds like there's a downside...


Most prevalent downside at present is the difficulty of getting a good
one for a reasonable price. Bike Tools Etc sells one made by YST, but
it's been disparaged for its relatively low durability. OTOH, at $17
plus shipping, it's one way to get a frame back in service quickly
when the threads have been damaged, and even if it only has a lifetime
of a couple of years in moderate service, that might be acceptable to
many riders.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.
  #13  
Old February 25th 06, 10:41 PM posted to rec.bicycles.tech
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Default Threadless BB Cartridges: Why/Why Not?

So far as I have known, the Mavic thread less BB cartage was for fixing
stripped out threads, when the bike owner didn't want to spend enough
$$$ to mill out the BB (frame) & re-thread for an Italian BB. Or the
frame already had an Italian BB. I've (correctly/incorrectly) thought
it was an inferior fix it terms of long-term reliability. And that JIS
version was even poorer.

John

  #14  
Old February 25th 06, 10:55 PM posted to rec.bicycles.tech
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Default Threadless BB Cartridges: Why/Why Not?

J. Brandt wrote:

Just to give an idea of the fragility of BB retention, I recently had
the right hand cup loosen and not be tightenable. When I removed it,
I discovered that more than 100000 miles of riding had eroded the
threads from the steel BB shell. The right side thread was completely
gone and the left side close behind. The right hand cup had been
brutally tightened and never removed during that time. Fretting
gradually ate up the threads leaving nothing but grey paste.


Jobst

I don't see how you can seriously use the terms "fragility" & "100,000
miles" in the same paragraph.
It would probably take a pile of 100 bikes @ a scrap yard, to have
acclimated that kind of mileage or a pile of 10 bikes of the average
rbt reader :/)

John

  #15  
Old February 26th 06, 03:49 AM posted to rec.bicycles.tech
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Default Threadless BB Cartridges: Why/Why Not?


Johnny Sunset aka Tom Sherman wrote:
Is this the referenced BB? See
http://www.bikepro.com/products/bottom_brackets/mavic.html.

Yes. Here's a slightly better pictu
http://www.zefal.com/stronglight/pag...keyProd=jp1000

"JP 1000". This photo almost shows the beveled tightening rings (alloy)
*and* the thin plastic washers that fit in between the rings and the
chamfered BB shell. Also almost shown, the outer, threaded adjustable
(pin spanner), cicular alloy side plates, approx. 6mm thick, with
o-ring around the outer circumference, but not the inner, where the
axle pokes through. Roller bearings ride on shoulders on the crank
axle. I've used a bike thus equipped for awhile, seems to work ok in
spite of a lack of axle shaft seal-- maybe some Campy-style threads in
there would be good; of course that would make it even more expensive.

I don't think they sell for more than other cart. BB setups, though I
haven't checked prices in awhile.

Seems like a pretty good solution, maybe analagous to conical fit
between crank (arm) and pedal spindle. --D-y

  #16  
Old February 26th 06, 05:13 AM posted to rec.bicycles.tech
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Default Threadless BB Cartridges: Why/Why Not?

In article ,
wrote:

Just to give an idea of the fragility of BB retention, I recently had
the right hand cup loosen and not be tightenable. When I removed it,
I discovered that more than 100000 miles of riding had eroded the
threads from the steel BB shell. The right side thread was completely
gone and the left side close behind. The right hand cup had been
brutally tightened and never removed during that time. Fretting
gradually ate up the threads leaving nothing but grey paste.


One idea I've considered is to have a bottom bracket shell cut
across the bottom, and clamp lugs (like seatpost clamp ears) across
the cut, or perhaps external clamps outside each cup. This would allow
the BB shell to be clamped down on the cups and arrest this fretting.

I'm not sure how good my intuition is for the magnitude of
forces encountered here, but the existance of bottom brackets
with extensive cutouts suggests to me this may be reasonable. The
torsion coming from the downtube would be the same order as what the
handlebar clamp supports, and this is a much larger interface which
should support it easily. On the other hand, vertical pedalling loads
and chain tension that the handlebars don't experience, would be
acting here. I think the chain tension would be benign though, being
in a direction that wouldn't act to open this split.
Vertical loads, I don't expect to be an issue as long as the
clamping is intact, but would be an issue with a clamp bolt failure.
I'm not sure that the BB cups are wide enough to allow for redundant
clamping here.

-Luns
  #17  
Old February 26th 06, 09:14 AM posted to rec.bicycles.tech
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Default Threadless BB Cartridges: Why/Why Not?

john Drew writes:

Just to give an idea of the fragility of BB retention, I recently
had the right hand cup loosen and not be tightenable. When I
removed it, I discovered that more than 100000 miles of riding had
eroded the threads from the steel BB shell. The right side thread
was completely gone and the left side close behind. The right hand
cup had been brutally tightened and never removed during that time.
Fretting gradually ate up the threads leaving nothing but grey
paste.


I don't see how you can seriously use the terms "fragility" &
"100,000 miles" in the same paragraph. It would probably take a
pile of 100 bikes @ a scrap yard, to have acclimated that kind of
mileage or a pile of 10 bikes of the average RBT reader :/)


The people with whom I ride often total more than 10,000 miles per
year as I have. My Campagnolo hubs from the 1970's are still serving
well and I expect the frame to retain its "static" BB threads at least
as well. The point is that crank threads and BB threads are dynamic
and constantly moving, although they shouldn't. That is why left hand
threads are used there.

If you ask why we have left hand threads, most shops will
mater-of-fact tell you so they don't unscrew. If you then ask why
these threads aren't tightened, you will get a blank stare. Of course
we tighten them is the reply. So how do they unscrew? These are
classically improper designs and I don't believe anyone has attacked
the BB problem although I have modified my cranks so that pedal
threads don't move and cause crank failures of which I had many. I no
longer need left hand threads on the left pedals.

Because right threaded left cranks are rare and right-right pedal
pairs even rarer, I still use left threaded left pedals.

Jobst Brandt
  #18  
Old February 26th 06, 09:21 AM posted to rec.bicycles.tech
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Default Threadless BB Cartridges: Why/Why Not?

someone writes:

Is this the referenced BB? See
http://www.bikepro.com/products/bottom_brackets/mavic.html.


Yes. Here's a slightly better pictu
http://www.zefal.com/stronglight/pag...keyProd=jp1000


"JP 1000". This photo almost shows the beveled tightening rings
(alloy) *and* the thin plastic washers that fit in between the rings
and the chamfered BB shell. Also almost shown, the outer, threaded
adjustable (pin spanner), circular alloy side plates, approx. 6mm
thick, with o-ring around the outer circumference, but not the
inner, where the axle pokes through. Roller bearings ride on
shoulders on the crank axle. I've used a bike thus equipped for
awhile, seems to work OK in spite of a lack of axle shaft seal--
maybe some Campy-style threads in there would be good; of course
that would make it even more expensive.


I see no additional information in this picture and don't believe it
addresses the problem at all, other than give the user a second chance
for BB treads to fail. The second time faster, because they are finer.

I don't think they sell for more than other cart. BB setups, though I
haven't checked prices in awhile.


Seems like a pretty good solution, maybe analogous to conical fit
between crank (arm) and pedal spindle. --D-y


Not at all. I see no press fit between the threaded cylinder and the
conical centering rings. Besides, how is the spindle retained and how
are the bearings held in the tube? Both of these present greater
fretting problems than a conventional cup BB.

Jobst Brandt
  #19  
Old February 26th 06, 09:25 AM posted to rec.bicycles.tech
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Default Threadless BB Cartridges: Why/Why Not?

Luns Tee writes:

Just to give an idea of the fragility of BB retention, I recently
had the right hand cup loosen and not be tightenable. When I
removed it, I discovered that more than 100000 miles of riding had
eroded the threads from the steel BB shell. The right side thread
was completely gone and the left side close behind. The right hand
cup had been brutally tightened and never removed during that time.
Fretting gradually ate up the threads leaving nothing but grey
paste.


One idea I've considered is to have a bottom bracket shell cut
across the bottom, and clamp lugs (like seatpost clamp ears) across
the cut, or perhaps external clamps outside each cup. This would
allow the BB shell to be clamped down on the cups and arrest this
fretting.


That is an idea. but that makes the BB an open sided tube that has no
torsional strength, and there is a rotating force there or the right
hand cup wouldn't need a left thread.

I'm not sure how good my intuition is for the magnitude of forces
encountered here, but the existence of bottom brackets with
extensive cutouts suggests to me this may be reasonable. The torsion
coming from the downtube would be the same order as what the
handlebar clamp supports, and this is a much larger interface which
should support it easily. On the other hand, vertical pedaling loads
and chain tension that the handlebars don't experience, would be
acting here. I think the chain tension would be benign though, being
in a direction that wouldn't act to open this split.


Cut-outs OK but not slotted crosswise.

Vertical loads, I don't expect to be an issue as long as the
clamping is intact, but would be an issue with a clamp bolt failure.
I'm not sure that the BB cups are wide enough to allow for redundant
clamping here.


I'm sure that is OK, bu the forces on the shell are not so simple as
they first appear judging from the need for a left thread.

Jobst Brandt
  #20  
Old February 26th 06, 06:47 PM posted to rec.bicycles.tech
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Default Threadless BB Cartridges: Why/Why Not?

Luns Tee wrote:

One idea I've considered is to have a bottom bracket shell cut
across the bottom, and clamp lugs (like seatpost clamp ears) across
the cut, or perhaps external clamps outside each cup. This would allow
the BB shell to be clamped down on the cups and arrest this fretting.


I have a ~30 year old frame (Belgian) that has exactly this setup. The
BB shell has 2 slots with ears and pinch bolts to clamp both the fixed
and adjustable cups. I assumed, given the age of this bike, it was a
well-known technique. I wondered why it isn't used more often.
 




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