> > I suspect you mean ECCENTRIC bottom bracket. The spindle is mounted in an eccentric, which when
> > turned, will tighten and loosen the chain as appropriate. They are found wherever chain tension
> > must be adjusted in the absence of a sprung derailer, such as a single speed with vertical
> > dropouts, or the front chain on a tandem.
"Alexander Kahn" <
[email protected]> wrote in message
news:[email protected]...
>
[email protected] Aha, that is what i mean. Now I see what's going on on those Jericho frames
> and that Phil Wood frame... Thanks. What tools are needed to adjust this type of bottom bracket
> (for the chain tension)? Does the frame need to allow for a special bottom bracket?
Indeed the frame's "hanger" or "bottom bracket shell" is usually made much larger to accomodate an
eccentric. Ideally the eccentric is large enough to allow 1/2" of total fore/aft adjustment, the
length of a chain link. Eccentrics usually have normal ISO threading, so any crank bearing assembly
may fbe fitted. Most models are simply held in place with a pairof allen bolts.
http://www.yellowjersey.org/photosfromthepast/ECC_MUZI.JPG
Note the binder bolts on the left in the photo. They are regular seatpost binders. You can see how
the aluminum liner rotates to change the position of the crank spindle relative to the rest of the
bike. The binder bolts need not be tight at all - much less than a seatpost bolt's torque - as there
is no force acting to turn the eccentric. Santanas for example use a 5mm grub screw with a 3mm allen
key head and that's probably overkill.
--
Andrew Muzi
http://www.yellowjersey.org Open every day since 1 April 1971
