H
Hank
Guest
On Mar 28, 10:28 pm, jim beam <[email protected]> wrote:
> [email protected] wrote:
> > Tom Sherman wrote:
>
> >>> The current design of the BBs one of the last holdovers from
> >>> ancient times that is still a perpetual problem. As I mentioned
> >>> before, if it has a left hand thread, the design is faulty, the
> >>> thread being a crude patch for the design problem, just as it is
> >>> for pedal threads that fail in spite of the orientation.
>
> >>> Left hand threads are used to cover for a moving interface that
> >>> tends to unscrews itself in use. As is visible on pedal crank
> >>> faces, pedals regardless of tightening, move in their contact with
> >>> the crank and by fretting erode the crank face. This erosion leads
> >>> to cracks that cause pedal eyes to fracture and throw the rider to
> >>> the ground if standing at the moment of failure.
>
> >>> Like pedals, BB cups also fret in the BB shell but, with the larger
> >>> thread, were moderately secure with right hand threads if tightened
> >>> to nearly unmanageable torque. That is why left hand threads are
> >>> used today to hide that they move. In time, the threads of the
> >>> right hand cup or BB shell become eroded to oblivion in time
> >>> depending on which of the two is the harder material. With steel
> >>> hardened bearing cups, the BB shell loses all its threads while
> >>> with aluminum cups, the right hand cup loses its threads.
>
> >>> Shimano has used a clamping method for left crank attachment to the
> >>> spindle that would also work for the BB. Meanwhile, cartridge
> >>> bearings fret on the inside and outside while the retaining cup
> >>> frets in the BB shell. That is what is wrong with the current
> >>> design especially with cartridge bearings.
>
> >>> In the short term, the current design works if monitored often and
> >>> maintained, but when the thread is gone, it presents a difficult
> >>> problem.
>
> >> I just throw out the bicycle if I have problems with the bottom
> >> bracket.
>
> > In contrast, I had my involuntarily threadless BB bored out and a
> > hardened threaded steel sleeve silver soldered to keep my custom frame
> > of many years in service.
>
> otoh, by not simply replacing a worn out frame, you're deliberately
> avoiding bothering to research improvements in frame design such as
> over-size tube which help mitigate shimmy. or aluminum. or carbon. as
> someone that like to express opinion on these materials, the least you
> should do is bother to actually use them.
>
> > I have a great frame builder and bikie
> > friend who has great metal working skills who also made the pedal
> > crank modification which solved the pedal to crank problem.
>
> what "crank problem" is that? when is the last time you saw pedal eye
> breakage on an "unmodified" crank?
For me, it was about a year ago - at least, a significant crack that I
caught (by sound, which is saying something, because I'm hard of
hearing) before it broke, on a 9-speed Veloce LH arm.
> [email protected] wrote:
> > Tom Sherman wrote:
>
> >>> The current design of the BBs one of the last holdovers from
> >>> ancient times that is still a perpetual problem. As I mentioned
> >>> before, if it has a left hand thread, the design is faulty, the
> >>> thread being a crude patch for the design problem, just as it is
> >>> for pedal threads that fail in spite of the orientation.
>
> >>> Left hand threads are used to cover for a moving interface that
> >>> tends to unscrews itself in use. As is visible on pedal crank
> >>> faces, pedals regardless of tightening, move in their contact with
> >>> the crank and by fretting erode the crank face. This erosion leads
> >>> to cracks that cause pedal eyes to fracture and throw the rider to
> >>> the ground if standing at the moment of failure.
>
> >>> Like pedals, BB cups also fret in the BB shell but, with the larger
> >>> thread, were moderately secure with right hand threads if tightened
> >>> to nearly unmanageable torque. That is why left hand threads are
> >>> used today to hide that they move. In time, the threads of the
> >>> right hand cup or BB shell become eroded to oblivion in time
> >>> depending on which of the two is the harder material. With steel
> >>> hardened bearing cups, the BB shell loses all its threads while
> >>> with aluminum cups, the right hand cup loses its threads.
>
> >>> Shimano has used a clamping method for left crank attachment to the
> >>> spindle that would also work for the BB. Meanwhile, cartridge
> >>> bearings fret on the inside and outside while the retaining cup
> >>> frets in the BB shell. That is what is wrong with the current
> >>> design especially with cartridge bearings.
>
> >>> In the short term, the current design works if monitored often and
> >>> maintained, but when the thread is gone, it presents a difficult
> >>> problem.
>
> >> I just throw out the bicycle if I have problems with the bottom
> >> bracket.
>
> > In contrast, I had my involuntarily threadless BB bored out and a
> > hardened threaded steel sleeve silver soldered to keep my custom frame
> > of many years in service.
>
> otoh, by not simply replacing a worn out frame, you're deliberately
> avoiding bothering to research improvements in frame design such as
> over-size tube which help mitigate shimmy. or aluminum. or carbon. as
> someone that like to express opinion on these materials, the least you
> should do is bother to actually use them.
>
> > I have a great frame builder and bikie
> > friend who has great metal working skills who also made the pedal
> > crank modification which solved the pedal to crank problem.
>
> what "crank problem" is that? when is the last time you saw pedal eye
> breakage on an "unmodified" crank?
For me, it was about a year ago - at least, a significant crack that I
caught (by sound, which is saying something, because I'm hard of
hearing) before it broke, on a 9-speed Veloce LH arm.
