Andres Muro said:Quoted message said:Quoted message said:>>>> Square taper to Octalink to ISIS to outboard bearings. �Do
>>>> the outboard bearings really make for a useable and/or
>>>> noticeable difference over older systems? Would especially
>>>> like to hear from anyone who switched out an ISIS or Octalink
>>>> for a current outboard bearing type of crank.
Quoted message said:Quoted message said:Quoted message said:>>> Outboard bearings was the 'solution' to the poor design
>>> Octalink,
Quoted message said:Quoted message said:Quoted message said:>> sorry peter, that's not an accurate assessment - octalink is an
>> excellent design solution to a very real problem. while it may
>> not have been an everyday occurrence, the physical design of
>> square taper renders it more susceptible to fatigue than the
>> larger pipe spindle designs:
Octalink is not a good design because it has torsional backlash. That
is, its splines are a free fit that under load exhibits small backlash
and this small rotation unscrews the retaining bolt. It does this
gradually every time the rider stands on the pedals with the right
foot forward (the only time the spindle transmits reverse torque).
This goes to the point where there is insufficient engagement of the
short spline and the ends shear off. Shimano, thnking their spline
was not long enough, lengthened the spline a little for the second
version, which also had the same problem.
That is why Octalink failed and is cancelled.
http://pardo.net/bike/pic/fail-001/spindle-fail-001.jpg
Quoted message said:Quoted message said:Quoted message said:>> it's simply a function of skin stress. larger diameter means
>> lower stress and thus less fatigue. thus, octalink showed the
>> way to solution. continuing from that, the next step has to be
>> outboard bearing because it's not possible to get a larger
>> spindle inside a standard bb shell and still have bearings
>> inside as well. all the bleating about the supposed "poor
>> design" of octalink was generated by jobst brandt who, somewhat
>> typically, failed to notice one of its small but very important
>> design features and thus he criticizes octalink for a failure
>> mode that doesn't exist.
Not so. Stresses are not to high in htese designs. The problem is
that they don't work in the manner the designer visualized the problem
as with the Octalink spline in which torsional backlash was not
understood. The same occurs with stacked-gear driven overhead cams in
motors. The gears all have torsional tooth backlash even though there
is no slack during amnual adjustment. When running, thse cam drives
and cams make a horrible chatter as the backlash slaps back and forth.
Quoted message said:Quoted message said:Quoted message said:>>> followed by the poor ISIS. Nether were an improvement to
>>> square taper, just something 'new' started in 1997 by shimano.
>>> Being the gorilla, Octalink(that shimano never licensed BB
>>> wise), waned and shimano started outboard bearings, and all
>>> crank makers came on board with, Campagnolo being the last to
>>> market it. Octalink and ISIS answered no question, solved no
>>> problem with regards to square taper but you see what the
>>> market has done. BB30 is being embraced by frame makers, along
>>> with 1 1/4 and 1.5 inch lower headtubes because it makes it
>>> easier(cheaper) for frame makers to hook great big tubes to
>>> bigger tubes(BB shell and headtube). Crank makers that are
>>> embracing BB30 are assuming all frame makers are going to go
>>> that way, but we'll see. FSA hasn't seen a new idea it didn't
>>> like as shown by their speed in making an ISIS, then outboard,
>>> then BB30 crank. A gent from FSA once told me right after they
>>> started the outboard bearing design they would rather copy than
>>> create.
Quoted message said:Quoted message said:Quoted message said:> It is interesting that all of those are '70/80s Campy NR spindles
> from open bearing BBs. Are there pictures of Shimano cartridge
> BB square- taper spindles failing? Not saying they didn't, but I
> never saw one fail -- just had bearings go south after many, many
> miles of riding.
Quoted message said:Quoted message said:Quoted message said:> I killed ISIS (and to a lesser extent Octalink) bearings in short
> order -- within a few thousand miles. The latest one was an
> expensive FSA -- but FSA would not touch it because the company
> had abandoned ISIS. As it turned out, I had broken the ISIS
> crank, too. The female insert in the CF arm had cracked all to
> hell. FSA did not have a replacement arm because, again, they
> had abandoned ISIS. I now have expensive key chain fobs. -- Jay
> Beattie.
Quoted message said:Quoted message said:Quoted message said:Not to mention that there were many thousands of square taper
Campag BB spindles and the percentage of breakage was low. I
didn't keep the 3 octalink BBs that I replaced that broke in the
center of the spindle
Quoted message said:Quoted message said:you really should have - these are the first I've ever seen
reported. next one you get, please post here - I'd love to examine
it.
Quoted message said:Quoted message said:Quoted message said:nor the octalink cranks that failed from 'lash, mostly MTB ones
where a rider gets airborne and then lands. To state that
Octalink and ISIS was produced by shimano and others to fix the
huge square taper breakage problem of Campagnolo is silly.
Ot's not the airborn part that causes this problem but rather riders
who stand with the right foot forward which causes reverse torque on
the spline.
Quoted message said:Quoted message said:one more problem with square taper and "lash", I've had a number of
them work loose over the years. and on many occasion I've stopped
to help mtb riders with that problem too. I've never had an
octalink crank work loose and I've never had to stop and help
anyone else with a loose octalink crank either.
You didn't have any goofy footed riders!
Quoted message said:Square tapers will work loose if not properly installed pretty
quickly, not over the years. If they are properly installed, they
will not work themselves loose. Octalinks and Isis have only been
sold for two to three years and then they were discontinued. I am
sure that if they are properly installed, they will last for a long
time. However, too many reports of failures lead to them being
redesigned. Square tapers have been in existence for several
decades, so comparisons in terms of durability are not adequate.
Since people would report failures w/ octalink and the did not offer
an incredible advantage over square taper, they were abandoned soon.
If a square taper is not installed with adequate torque, it will lift
off and deform the compression side of the contact faces. Once this
occurs, the crank of a goofy footed rider will repeatedly loosen as it
rotates into the deformed formerly square bore.
Quoted message said:Regarding people that you will find with loose BBs, that is likely
in cases were people just purchased a new bike that was not properly
adjusted, or people who recently had a tuneup and the bb had not
been properly tightened. That, or they rode five times in five
years. If you use plumbers tape on the crack bolts, the don't work
themselves loose even if they are poorly tightened.
Loose BB is loose ball bearings, not a crank attachment problem.
Therefore, it is unrelated to the type crank attachment.
Quoted message said:A problem that I would find with square tapers were on the Italian
threaded ones. They required that the fixed cup would turn in a
direction that would work itself loose unless it was really tight in
the BB shell. This requires either a fancy and expensive Hozan tool
that held the cup wrench in place to tighten the fixed cup, or a
home made devise that would do the same function. Most shade tree
mechanics and a bunch of bike shops had neither. This would lead
new Italian threaded bike BBs to work themselves loose.
I think this has drifted into foreign territory. BB adjustent and
crank attachments are unrelated design problems. Aside from that, as
I have mentioned before on this forub, wherever you find a left hand
thread in a structural attachment, you are looking at a faulty design.
That goes for BB's, pedals, or auto left hand wheels of old.
The left hand thread is used where the retaining screw is being used
to support a rotating load. Screws are suppoed to supply compression
force between two mating parts. Radial loads should not be carried or
the part will displace radially. As I pointed out, precession is not
understood by most engineers and that is why such designs get to
market.
Octalink fails because it cannot reliably support reverse torque.
Jobst Brandt