Cause of spalled cones? Was getting a sort of rubbing sound from my front wheel, like rubbing brakes, but the sound continued even with the bridal loose.  So I disassembled my front hub.  Everything looked good until I got to the cones.  One has a rather noticeable line worn by the balls (more so than I've seen on other bearings), and the other has what I would call a spalled spot in addition to the line, with a rough, wavy area for maybe 15 degrees of arc.  The cups, on the other hand, look factory fresh.  This is a Shimano RSX hub.

Any idea what would cause this?  The hub has 25-30K miles on it, but has been overhauled twice.  The sound came up over a period of maybe 100-200 miles riding.  I don't go off-road and I don't jump curbs.

Anyway, since the cups look good and the rim probably still has another 10-20K of life left, I'm thinking of getting a new hub and just swapping the cones, vs replacing the hub or buying a new wheel.  Any reason not to do this?

More info:  I took a closer look at the cones.  One is not really that worn -- there's just a barely-perceptible mark from the balls, and I'd not suspect it at all if it weren't for the other cone.  The other is spalled to one degree or another all around, however.  

And, oddly, the two cones are not identical.  The "good" one has the plastic seal washers, while the "bad" one has no groove for seal washers.  Clearly, one or the other (probably the "bad" one) has been replaced in one of the two bike shop overhalls.

So the question is, why was the old cone replaced?  Presumably it was spalled as well, so what could be causing one cone to spall?

I haven't removed the dust caps, so I can't get a REAL good look at the cups, but will have a shot at it again, using a flashlight.  But on my several inspections so far the cups look smooth and shiny.  And I'm certain the balls were replaced the last time around.  (Unfortunately, inspecting 18 tiny ball bearings is just about impossible.)

Here are pictures:




Unfortunately, my camera only does a middling job with macro photography.  In the first shot the bad cone is on the left and the good (stock Shimano) one is on the right.  The second shot is the bad cone removed from the axle.  The line you can see, up close, looks kind of like a bead of weld, with "puddling" -- little dents kind of pushed up against each other.

When I went to remove the cone I discovered that it was very difficult to remove.  Something had snarled the threads on the axle, at about the junction point between the cone and the lock nut.  It was impossible to say with any certainty, but it looked like the axle was very slightly bent at that point.  It may be that a bent axle was the cause of the failure (though I don't know how it would have gotten bent, or how a bend at that point could cause a bearing failure).

Anyway, swapped in the axle from a new hub (also replaced the balls and repacked it) and the noise seems to be gone (though hard to tell for sure, as it was so windy for my test ride).

Grrr!!! 

The noise is back, with the new axle, cones, and balls.  Have not taken it apart yet, but I'm guessing one of the cones will be pitted when I do.

And looking for a new wheel, I can't find anything on the internet.  It's a Shimano HB-A410 hub, Mavic 622x18 rims, 36 hole.  So far I've not found any 36-hole front wheels, and most of the 622 road wheels I find are "aero" -- not exactly the style for my touring bike.  I'll check the local shops to see what they can get -- failing that I suppose I'll have to build my own.

"Final answer": Pretty much convinced that the hub was bent and came that way from the factory.  This is consistent with the repeated spalling and the damage to the axle that I found.  Replaced with a nearly identical wheel from Peter White and things seem fine.
Time traveling here...

If that type of spalling occurs after several thousand miles, then that's most likely normal wear from the little bit of play vs road vibration, etc.

If that occurs within 200 miles, then it means your cone nuts are too tight.  Some people here say there should be no play, but that is incorrect.  There should be a tiny bit of play in the axle/bearings.  If you smack the axle, you should hear it tap lightly.  

If you have it too tight, you'll feel very little or zero play, but when you twist the axle by hand, you will feel it grab or catch very slightly.  Or, if you hold it by the axle ends and spin the wheel, you'll see it grab periodically (change in friction makes it twist a little in your hands).

That is the minor imperfections in the races and the bearings fighting each other.  There should be just a tiny bit more space than the largest imperfection combinations (for a micron or two of grease).  That means, most of the spacing will have just a tiny bit of play.

I find that every hub is a little different, but it usually takes 5-10 tweaks to get just the right amount of play when reassembling the wheel bearings/axle/cones/locknuts.