From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.misc,rec.bicycles.tech
Subject: Re: Headset, how loose?
Date: 12 Sep 1997 23:49:56 GMT

David Summers writes:

(musing about head bearing adjustment)

> On the new bike, it's a bit stiffer.  I don't feel any binding or
> anything like when bearings are too tight, but it does take a smidge
> of a push to turn rather than (if you pick it up) "flopping around"
> like the old one.

With the handlebars in place the head bearing clearance cannot be
easily assessed the way it can with a bare road fork by rotating it
with the fingers.  With a bare fork the drag or clearance can be felt
easily, however, with handlebars in place a more complex method must
be used because the mass of the components obscures the feel.
Suspension forks present more problems that can be solved similarly.

For tightness lift the bicycle, front wheel installed, so that the
wheel prefers to hang straight ahead but flops to the side if the
frame is tilted back.  At the balance point where the wheel just
prefers to swing straight ahead, lean the frame side to side lightly,
upon which the wheel should swing freely.  If it appears to jumps
between light detents, it is too tight.

For looseness, bounce the front wheel of the bicycle by raising it off
the ground by grasping the elbow of the bar stem in one hand.  A loose
head bearing will make a dull chatter as the rigid fork resonates.
This only works for bicycles that have no loose components, like a
rattling fender or handlebar bag, and not for suspension forks.  It
also requires that the front wheel and crank spindle bearing not have
clearance.  Both of these elements can emit sounds similar to a loose
head bearing from this test.

For suspension forks, that would dampen any bounce, rocking the bike
back and forth with the front brake locked gives a feel for clearance
at the external gap between cup and cone of the upper head bearing.
By placing the fingers over the two bearing halves, motion can be felt
if the bearing is too loose.  This also works with rigid forks but the
bounce method is simpler and more diagnostic.

Adjust the bearing so that no clunk remains during the bounce test and
that the front wheel turns freely from side to side in the swing test.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Headset, how loose?
Date: 14 Sep 1997 02:39:04 GMT

Gordon Renkes writes:

>> For looseness, bounce the front wheel of the bicycle by raising it
>> off the ground by grasping the elbow of the bar stem in one hand.
>> A loose head bearing will make a dull chatter as the fork
>> resonates.

> I have always done this by grabbing the front brake, and rocking the
> bike forward and aft, in order to feel any looseness.  Is your
> method more reliable, or more sensitive?  Or just another way to do
> it?

It is more sensitive because while rocking the bike back and forth,
some rotation may be involved and this obscures relative induced
clearance motion.  The brake method works OK, especially if you have a
suspension fork or fender or handlebar bag.  The best for a rigid fork
bike is to adjust it before the bars are installed.  That way you can
rotate the fork with your fingertips and fell the drag that should be
just a bit tighter than free.

Jobst Brandt      <jbrandt@hpl.hp.com>