From: BRANDT_JOBST/HP1900_01@HPLOMG.HPL.HP.COM
Newsgroups: rec.bicycles
Subject: Re: indexed steering? (I think I broke something)
Date: 12 Aug 92 22:16:29 GMT

Carl Baker writes:

> In the several years I spent working in a pro shop, I have never seen a
> case of "index steering" (yes, we called it that) that was _not_ caused
> by a "brinelled" headset - on with divots in the races.  I am 99.999
> percent certain that that is your problem.  What are you going to do if
> you don't fix it?  I suggest that you fix the headset even if you sell
> the bike, as a damaged headset could be grounds for a lawsuit if the
> buyer crashes.

I disagree on two points.  First, because the use of the term brinelling
conveys a notion as incorrect as the phrase "my chain stretched from
climbing steep hills" and second, because there is no possibility of
injury or damage from an "indexed" head bearing.

Damage to the head bearings seems to be twofold in this case because the
steering, if properly adjusted, only gets looser from dimpled bearings and
would not become arrested by the dimples.  So the head was adjusted too
tight or it got tighter inadvertently.  However, dimpling is caused by
lubrication failure and occurs while riding straight ahead.  This condition
is worsened by a tight bearing while a loose bearing would introduce more
lubricant if it were to rattle.

If you believe it comes from hammering the balls into the races, I suggest
you try to cause some dimples by hammering with a hammer onto the underside
of the fork crown of a clunker bike of your choice.  Those who pounded in
cotters on cottered cranks will recall no such dimpling on the BB axle and
even though this is a far smaller bearing race than a head bearing and the
blows are more severe and direct, no dimples was made.

Ball bearings make metal-to-metal contact only when subjected to fretting loads
(microscopic oscillations) while in the same position, as in riding straight
ahead on a conventional road.  If you watch your front axle while rolling
down the road at 20+ mph you will notice that the fork ends vibrate fore and
aft.  This motion arises not at the blade tips but at the fork crown and
articulates the head bearing in fretting motions that are not in the normal
direction of bearing rotation.  Any substantial steering motion replenishes
lubrication from adjoining areas.

Lubrication failure from fretting causes welding between the balls and
races and these tiny weld spots tear out repeatedly.  The result is that at
the front and rear of the races elliptical milky dimples occur.  Were these
brinelling (embossed through force) they would be shiny and round.  Various
testimonials for the durability of one bearing over another may be based on
good experience, however, the differences in most of these was not in the
design of the bearing but rather the type of lubricant used.  A ball bearing
is not suitable for this use.  This is in spite of their use in almost all
bicycles.

To reduce point loads and to protect the rolling elements from fretting
motion, roller bearing head bearings have been built.  In these the rotary
motion is taken up in needle bearings on conical races and the fork
articulation is absorbed by an approximation of a spherical cup (the steel
race) against the aluminum housing.  Both of these bearings are ideally
loaded.  The rollers all remain in contact and carry rotary motion while
the plain spherical bearing remains in full contact carrying low pressure
fore and aft motion.

I am disappointed that roller bearings until now have not been suitably
perfected to rid us of the age old bearing failure.  Maybe some day soon
Sun Tour, Campagnolo, Shimano or Stronglight will emerge with an easily
adjustable and fully compatible bearing.  The one I am using is durable but
not easily adjusted and it has too great a stack height to qualify for a
recommended replacement.

jobst_brandt@hplabs.hp.com
Newsgroups: rec.bicycles