Old 06-21-10, 07:52 PM
  #12  
dscheidt
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Originally Posted by BCRider View Post

So I guess that without seeing really good pictures of the damage in this case it is hard to say if it is a fore and aft only damage related to brinelling or spalling or if it's a full circumference damage that would indicate corrosion or poor lubrication and vibration based fretting.

But in the end one thing we can all agree on is that once the races are damaged to where you can see and feel a notchiness nothing is going to make the steering feel correctly smooth again. It's best to just bite the bullet and replace the headset once the races are not in ideal condition.
There are about a dozen ways to kill a bearing, short of a bomb. many real failures are a combination (bike gets ridden in the rain, gets water in the headset bearings. grease gets washed away, something rusts, rust causes mechanical damage (it's a decent grinding compound...)). Barden do a nifty pamphlet that explains some causes:
http://www.bardenbearings.com/scan pdf/Bearing Failure Brochure.pdf

Every headset that I've ever looked at with the indexing problem has had fretting damage. I've seen headsets that have failed for plain lubrication failure, from over tightening, from using lousy grease. But I've never seen a headset that wore the balls out.

Fretting is a pretty common failure in bearings that are exposed to vibration that they're not designed to cope with, as happens in storage, transport. It doesn't take much rotation of the ball to renew the film of oil, so it's rare to see it in bearings that rotate regularly.

Fretting is also a common cause of failure in parts that aren't supposed to move relative to each other -- like the left pedal to crank interface. If you have to change the threading to keep it from coming apart, you're doing something else wrong. Fretting used to kill car wheels, until spherical seat lugs were used. It's poorly understood, and widely ignored, because it's hard to understand.
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