*No heat*; the system is not designed for that. Moreover, heating is
not consistent because you cannot guarantee the temperatures when you
finally get the crank to the axle. Heating (properly) works for
bearings because they will always cool to the same size on the same
shaft. With a tapered interface, when the crank finally cools, its
position on the taper, and thus the resulting interface forces, are not
controlled.
Grease on the taper is recommended by Jobst Brandt, who is the leading
visible researcher in this area. When you torque on the crank if the
surface is not lubricated, the material (especially aluminum) will form
its own lubricant and "mush" along the surface, called galling. This is
uncontrolled and also deforms the crank.
_Friction_between_the_crank_and_axle_surfaces_performs_no_role_in_the_strength_and_fit_of_the_crank_.
It is the shapes of the two surfaces that is important. By greasing the
tapers, the interface between the two is controlled as much as possible
when the crank is installed. In addition, the grease helps protect the
interface from both corrosive and erosive destruction during use.
If you are having trouble with the cranks after using the instructions
that John Childs has listed, then
-the problem is with the cranks-. Don't risk your entire wheel trying
to get a bad set of cranks to stay on. Toss them and get another pair.
40 ft-lbs is about right; needing to go above that number means that
there is a problem.
Finally, there is a popular myth that the proper way to handle new
aluminum cranks is to carry a wrench and tighten them every once in a
while (when they become loose) until they finally settle in and stop
doing that. Although this is partly true, the truly proper way to do
this is to remove the crank, clean, regrease, and retorque it on, not
leave it on and keep tightening it. There is a "squirming action"
during riding which moves the crank around, towards the middle of the
axle slightly. This action results in a loose nut/bolt, but the crank
itself is actually higher on the taper and tighter. After several
successive applications of the wrench, the crank is on much tighter than
it should be, and its life is greatly shortened because long-term cracks
develop in the crank interface, especially in the corners.
So... the proper way to handle this is: after proper installation, go
for your ride. During the ride, keep the nut snug, but don't put any
oomph into it. After your ride, go home, remove the crank, and
re-install it, again with the proper torque. After a couple of rides or
so, the crank interface should slightly deform in the right places and
settle down.
Buying better quality cranks will make this whole process less obtrusive
on your riding, since the surfaces will be much more to spec, and the
material much stronger and more consistent.
For confirmation of the above, although with much less rider-friendly
terminology, see http://sheldonbrown.com/brandt/installing-cranks.html.
--
U-Turn - As long as my feet keep movin'...
Weep in the dojo... laugh on the battlefield.
'LiveWire Unicycles' (http://www.livewireunicycles.com)
'Strongest Coker Wheel in the World'
(http://www.unicyclist.com/gallery/albup39)
'29er Tire Study' (http://u-turn.unicyclist.com/29erTireStudy/)
'New York Unicycle Club' (http://www.newyorkunicycle.com)
-- Dave Stockton
------------------------------------------------------------------------
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