Dumb Motorcycle Steering Head Question

 My motorcycle has a lower steering stem which holds the forks and includes a
tubular piece of steel which comes up through the steering tube in the
frame.

On top, there is a a plate (fork bridge?) that fits over the steering stem
and attaches with a big nut.  It also has clamps for the forks and the
handlebar holders attach to it.

Dumb Question:  What prevents the fork bridge (on top) from rotating with
respect to the steering stem?

Is there some clever locking mechanism that prevents the fork bridge from
rotating on the steering stem, or is it the fact that the forks are clamped
at both the top and bottom that effectively joins the pieces together?

Thanks, Datesfat

 Datesfat Chicks wrote:

The latter.  Look at your forks.  There's two _very_ stiff ~40mm diameter
steel tubes connecting the upper and lower triple clamps (what you call
the fork bridge) together.  If you can bend them, you can twist the
steering stem... if not, it's not going to twist.

 

My condolences... mine's a solid axle.


That's the 'top triple tree'!  The pair is called the steering head
assembly, or 'triple trees'.


It is the triple tree clamp bolts.. the fork tubes are
an integral part of this assembly.  The torque for
the clamp bolts is very important... feel free to
obsess on this torque spec.
__
Steve
.

 wrote:

The tubular piece is the steering spindle.

That's the upper triple clamp.

The fork tubes would have to move away from being parallel to each
other.

This does happen after an accident that "tweaks" the fork tubes out of
parallel.


That's it.

If you look down at the handlebars and they are not at a 90-degree
angle to the
front wheel while the front wheel is pointed straight ahead, your
forks are "tweaked" out of parallel.

The solution to fix this problem is to loosen the triple clamp bolts
and the axle clamp bolts *slightly* so you can grip the front wheel
between your knees and
turn the handlebar so it's straight across the frame while the wheel
is pointed straight forward.

Then tighten the bolts.

If you want to do a decent fork alignment with simple tools, you can
use a tape measure to measure from the center of the front axle on
both sides to a point on the frame, and measure from the tops of the
two fork oil filler caps to a point on the rear fender.

When you have adjusted the fork tubes to the point where both sets of
dimensions are within 1/16th of an inch of each other, your forks are
straight enough for decent steering.

You can adust your rear wheel to be perfectly in line with the front
wheel by
taking 20 feet of string and pulling it through the wheel.

Then take one end of the string and walk it around the back of the
motorcycle and then walk back to the front.

Do the same thing with the other end of the string.

Then lay down in front of the motorcycle and pull the ends of the
strings tight.

The strings should touch the edges of the wider rear tire in four
places and the strings should be the same distance from the edges of
the front tire.

A decent alignment will result in the rear wheel and front wheel being
parallel to within about 1/16th of an inch.

But you shouldn't worry too much about fork and wheel alignment if
your tires are old and hard. An alignment won't stop the front wheel
from waggling side to side
if the rubber is dead.