Threadless BB Cartridges: Why/Why Not?

In article ,
wrote:
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

In article ,
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.

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 I can see how a freely rotating bearing would
load the BB shell in torsion, aside from precession which this clamping
should arrest.

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.

Cut-outs OK but not slotted crosswise.

Some pictures I've seen, have so little of the shell left
that I can't believe them to have any more torsional strength than the
split shell, the remaining shell being basically two independant
bands, one for each cup, and a large hole from chainstay lug to downtube.
But such extremes aren't that common and it's probably telling that
they're no longer commonplace.

I wasn't able to find any pictures to corroborate last night,
but some tandems with eccentric bottom brackets have shells that are
slotted all the way across. These are a larger diameter though, which
may help them deal with stresses.

My other thought for the moment is that since the dynamic loads
are mainly an issue on the right side, that a slot 2/3 the width of the
shell to allow clamping only on that side might be useful in its own
right without fully splitting the shell. Or, if there's merit in
clamping the left side too, then perhaps a separate parallel slot for
it - this would leave a continuous bridge of metal that can carry torsion
generated shear forces that the full split could not.

-Luns

On Fri, 24 Feb 2006 21:44:40 +0000, jobst.brandt wrote:

Pete Cresswell 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.

Some bikes came with pressed-in BB bearings, through the early 90s --
Klein and Fisher come to mind. I think there were others too. The
problem is getting the bearings replaced, if you can't do it yourself.

The Pinarello BB mentioned in this thread is probably pressed-in:

http://www.pinarello.com/eng/product...ology_gear.php

Pinarello uses pressed-in headsets too.

ISTR some older Kleins being creaky, and people trying to cure the
problems with Loctite. If there's enough action to wear your threads
away, there may be enough for a pressed in bearing to work loose.

The Pinarello unit has larger bearings around an ISIS spindle, requiring a
larger BB shell. Perhaps the greater outside diameter of the bearing
makes it less susceptible to working loose.

Matt O.

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.

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.
-snip-

I don't think that sounds too promising. But in the '50s and
'60s the British frame shops made a similar beginning. To
cure a stripped shell, they slit the bb crosswise, forced
the edges together, welded the seam and rethreaded the
resulting smaller bore.

Here, we're partial to building up a bronze fill then simply
cutting a new thread where the damage is half a thread deep.
Like this but inside-out:
http://www.yellowjersey.org/FORKTHRD.JPG

For fully missing threads, we bore out and either cut to
Italian or braze in threaded rings as JObst described earlier.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

wrote:
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.

Past here it depends on your curiousity. --D-y

Luns Tee writes:

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 I can see how a freely rotating bearing would load the
BB shell in torsion, aside from precession which this clamping
should arrest.

It's not the bearing, there or in the pedal, that unscrews the thread,
but rather precession from a rotating load point. I suppose if the
clamp is sturdy, it could arrest any fretting between cup and shell.

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.

Cut-outs OK but not slotted crosswise.

Some pictures I've seen, have so little of the shell left that I
can't believe them to have any more torsional strength than the
split shell, the remaining shell being basically two independent
bands, one for each cup, and a large hole from chainstay lug to
downtube. But such extremes aren't that common and it's probably
telling that they're no longer commonplace.

This is like other places on bicycles, where someone with enough
market presence can set a new standard for mechanics. It took a long
time for the four kinds of BB threads to arrive at the British
standard, odd as it is, of 1.370x24TPI Left & Right threads.

http://www.sheldonbrown.com/brandt/bb-adjust.html

I wasn't able to find any pictures to corroborate last night, but
some tandems with eccentric bottom brackets have shells that are
slotted all the way across. These are a larger diameter though,
which may help them deal with stresses.

I think that this problem could be overcome but I don't see it
happening with the extreme attention to weight savings. We won't see
a heavier BB shell with a split and clamp screws in the bear future.

My other thought for the moment is that since the dynamic loads are
mainly an issue on the right side, that a slot 2/3 the width of the
shell to allow clamping only on that side might be useful in its own
right without fully splitting the shell. Or, if there's merit in
clamping the left side too, then perhaps a separate parallel slot
for it - this would leave a continuous bridge of metal that can
carry torsion generated shear forces that the full split could not.

That would be practical, considering that the left cup does not have
any significant rotating loads, proven by the use of right hand thread
and an aluminum lock ring that seems never to change its preload.

Jobst Brandt

Does the Cannondale Hollowgram SI integrated BB qualify as threadless?

both my road bike and MTB have them with some very tough miles on the
MTB and a year of racing on the road bike. Claims to be lighter and
stiffer than the equivalent Dura-Ace.

http://www.cannondale.com/Asset/iu_files/115861a.pdf

charlieb in ct

On Mon, 27 Feb 2006 02:34:37 GMT, Charles Beristain
wrote:

Does the Cannondale Hollowgram SI integrated BB qualify as threadless?

both my road bike and MTB have them with some very tough miles on the
MTB and a year of racing on the road bike. Claims to be lighter and
stiffer than the equivalent Dura-Ace.

http://www.cannondale.com/Asset/iu_files/115861a.pdf

It's a proprietary interface crankset which requires a special BB
shell in the frame. These cranksets fit only a CDale frame that's
prepped at the factory to receive them. The frames might be
retrofittable to accept a different crank, but I can't tell; no
dimensions are given, so it's impossible for me to say whether the BB
might be threadable to accept a conventional BB.

Despite the fact that CDale is an established firm with a long record,
I would tend to regard these cranks as something to be avoided due to
the inherent pitfalls of the proprietary-parts problem.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

In article ,
Peter Cole wrote:
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.

I would imagine that the purpose of this pinching was either
simply forgotten, or deemed not worth the extra complication and
weight (and then forgotten).

I'm curious though - what's the threading of this BB? Is the
right side cup a normal or a left-handed thread?

-Luns

Luns Tee wrote:
In article ,
Peter Cole wrote:

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.


I would imagine that the purpose of this pinching was either
simply forgotten, or deemed not worth the extra complication and
weight (and then forgotten).

I'm curious though - what's the threading of this BB? Is the
right side cup a normal or a left-handed thread?

-Luns
often standard BSA, but variations exist

See www.m-gineering.nl/oldtechg.htm (last entry)

--
---
Marten Gerritsen

INFOapestaartjeM-GINEERINGpuntNL
www.m-gineering.nl