Re: Headset cheap fix - works

Donald Gillies <[EMAIL PROTECTED]> writes:

>>>> One of the A9s finally indexed on our tandem. Photo here:

>> http://www.geocities.com/dianne_1234/bikes/index.html

>>> That's an interesting pic!

>>> Maybe I'm just seeing what I want to see, but it appears that you
>>> have classic Brinelling going on there.

>>> i.e.
>>>           _
>>>          / \
>>>          \_/   < crater "lip"
>>> ______/\    /\______
>>>          \_/

> I have a very old headset from someone else's bike that I'm
> interested in trying to restore (rather than discard).  What do you
> think about this proposal for fixing the indentations in the races (I
> won't use "pitting" or "Brinelling" or "fretting", to avoid stirring
> up the mechE's on this list) :

> 1.  For each bearing race, take one side of the headset (cup or
>     race) and rotate by 1/2 the space between bearings.  Goal is to
>     reduce the pit depth halfway.

> 2.  For all 4 races/cups, rotate by 1/4 the space between bearings.
>     Goal is to have the "straight ahead" direction not correspond to
>     any particular pit orientation.

The dimples don't have any particular bias toward any location and for
typical old style fixed headsets with 20 bearing balls the dimples are
only 18 degrees apart just like the rollers in the picture offered at:

http://www.geocities.com/dianne_1234/bikes/index.html
    
> 3.  Remove the bearing retainer, add bearings until they don't all
>     seat, then remove 3 bearings, yielding a headset that's 2
>     bearings short of a full load.  Hearsay from Barnett's bicycle
>     manual.

That is correct.  That puts them at 16.363636... degrees apart.  From
this you can see that most of the balls will be teetering in or on the
edge of a dimple.  Get a new head set and while you're at it get one
of the Shimano, Cane Creek or King units that get around most of this
problem.

> 4.  Reinstall everything and pack headset until fork turns freely
>     with no front wheel / handlebar, but doesn't "click" when front
>     brake is locked and I'm on the seat and bike is rocked.

> 5.  Ride 1000 + mi on the headset to reduce or redistribute the
>     bearing indentations.

You can try this on a disassembled and cleaned bearing by placing the
balls in the race and rotating it under hand load on the table.  I
think you'll see a wave of dimple engagement wandering around the
bearing as it turns.  This is doomed to failure.  What have you got
against installing a new head set?  If it is antique consistency, just
ignore the dimples.  They are only functional for someone who descends
hard and rides rough roads where the clunks can be heard.

> 6.  Sand/re-finish the races and then re-chrome the headset to make
>     it look like new.  Will nickel plating of the chrome layer be
>     too soft for the headset races?  Should I mask off the races
>     before attempting to re-chrome this headset?  Or should I just
>     skip the nickel plating in the races?

It will flake off under load.  It is sub surface shear loads that
cause bearing races to spall.  These will spall immediately.


Jobst Brandt
[EMAIL PROTECTED]