BCRider

I had not heard about fretting before now. In looking up this failure mode all the examples I'm seeing are more related to lubrication failure via moisture or other corrosive contamination that leads to rusting of the bearing parts and a resultant pattern left etched into the races. The other reference to fretting that I found involved the races spinning in the housings or on the shafts independent of the bearings themselves.

I've seen a couple of headset races with a pattern like this and could not for the life of me figure out what the problem had been. I assumed that it was due to some rust from sitting and that the pitting had been "polished" out by further use until the races formed a little hill and dale like pattern. Now I realize that these races had failed from fretting be it corrosion based or lack of grease based.

What you go on to describe here sounds more like the references I found to a failure mode called "spalling" but not quite. Spalling, occurs where the instant point load goes well beyond what is needed to cause a brinnelling mark and a part of the race actually fractures and comes loose from the parent metal.

The difference seems to be that spalling or brinelling is localized to the fore and aft points and is more likely to occur in a bearing with incorrect preload while fretting is more likely to occur in a bearing with a lack of lubrication and where there is significant vibration being absorbed. Along with the fretted bearings I've observed I've also seen more than a few headset races and wheel bearing cones where the high point loaded spots are really badly worn into a deep notch or short groove due to the bearings pinching past those points rather than rolling smoothly. This failure mode was clearly due to either brinelling or spalling.

I also found the reference to Jobst Brandt on this and it would appear that you're a fan since this is pretty much a direct quote.


Your post about fretting got me curious so I went searching. I turned up this write up about bearing failure that is quite interesting. There's more ways to mess up a bearing than I thought....

http://www.brighthub.com/engineering...les/16068.aspx

Fretting in this article (in part 7) appears to be more related to the nature of the race mounted in the housing or onto a shaft. But there's other references to fretting on the actual bearing tracks to be found via google using "bearing fretting". They all seem to include references to corrosion. Fretting, from all the examples I can find, seems to be a more overall mode related more to bearing contamination due to corrosion or lubrication failure due to extreme vibration on standing bearings. The interesting thing is that this can occur, and in fact seems like it mostly occurs in bearings that are correctly preloaded but that are not in motion but where there is vibration applied to the bearing so that it still has to withstand a loading but without the aid of proper lubrication. But all the references I've seen for this sort of failure are all around the bearing instead of being limited to the fore and aft points. However there's no doubt that such damage would result in a notchiness or cogging.

From all this there appears to be four possible failure modes that are possible in a headset. Brinelling, spalling, fretting and finally just plain ol' splitting of the race that leaves a full depth crack that forms a gap.

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.