The problem with the square taper design is that there is no stop on the
hub/spindle to keep the cranks from sliding further up the taper when
you pedal really hard. When you pedal really hard (or land a drop) the
cranks will want to take some of that force and slide further up the
taper. When you relax your pedaling the cranks will slide back down
the taper. When the crank slides up the taper it reduces force on the
bolt or nut that is holding the crank from falling off the tapers. If
that force is reduced enough the bolt/nut can loosen by a fraction of a
degree. Then the crank slides back down and the bolt/nut is tight
again. That cyclic process means that the bolt/nut that holds the
crank on can eventually become loose enough for the crank to fall off
or the crank to become wobbly.
Medium strength Locktite (or generic threadlocker) on the threads of
the bolt or nut is enough to keep it from loosening on its own. If
that bolt or nut stays tight, and the cranks were properly installed,
and the taper on the cranks is not worn, the square taper setup can be
reasonably reliable.
There is no need to Loctite the taper itself. A little bit of grease
will do fine there. The Loctite is just needed on the threads of the
bolt or nut.
Dave Stockton wrote up 'a procedure for installing square taper cranks'
(http://tinyurl.com/blcbl). Follow that guide and your square taper
problems on a Coker or other unicycle will be mostly solved.
It is also important to use good cranks. Some cranks just have a wrong
taper that doesn't properly match the taper on the hub. Other cranks
are too soft and that allows the crank to move farther up the taper
during hard pedaling and are more of a problem. Some steel cranks have
a bad taper.
I've been using Kooka cranks on my Coker and have never had a problem
with a loose crank and I never expect to have a problem. They're the
custom Kooka cranks with three pedal holes (130, 150, 170). I
installed the cranks with Loctite when I first got them and haven't
touched the retaining bolts since. When I want to change crank length
I change the pedal position rather than changing cranks. I haven't
touched or checked the tightness of the retaining bolts since
installing the cranks (checking the tightness would break the Locktite
bond and require that I re-Loctite the bolt and if the Loctite is
holding there is no need to even bother). The steel square taper
cranks I have on my freestyle unicycle have also never come loose.
They've been on the unicycle for several years without me ever checking
the tightness of the retaining nuts (checking the tightness would break
the Loctite bond).
ISIS Drive would be preferable to the square taper. An ISIS wide Coker
hub would be nice especially now that there are suitable range of
lengths and styles of ISIS unicycle cranks available. With ISIS you
can forget about pretty much all of what I wrote above about square
taper cranks.
--
john_childs
john_childs (att) hotmail (dott) com
Team Never Wash Your Muni
'My Gallery' (http://tinyurl.com/3d57bn) :: 'Unicycling Bookmark List'
(http://backcountry.unicyclist.com/) :: 'World Clock'
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