I believe the Jobst fretting explanation.
Why do road bikes tend to fret or brinell with the forks straight? Because you don't move the bars much on a bike going straight on a road, you steer more with your body.
Early rigid mountain bikes ridden for hours on dirt roads did not seem to have fretted bearing surfaces as much as road bikes? The constant impacts on the races from the bearings a dirt road or trail would be greater than from a lightweight road bike ridden only on the road. A rider tends to move the handlebars more riding on less smooth surfaces.
Headset bearing adjustment is not always easy to get within the what, a thousandth of an inch? I think this can be for either or a combination of two reasons, the cup and cone surfaces are not parallel, and the threads on the fork are often buggered up a bit.
Many of the low to mid range Treks I saw in the early 80s needed head tubes and fork crowns faced. Loose headsets are not good for many reasons, especially for the threads on the fork. Non-parallel bearing surfaces do make it hard to get a good headset adjustment.
I am a believer in loose bearings on the lower headset, and caged bearings in the top. You can butter up the lower race to hold the bearings with the bike upside down in a shop stand, put the fork in and then work the top race and bearings on.
Motorcycles have these problems too, but most of the motorcycle maintenance books attribute it to impact. Try arguing the Jobst fretting theory to those guys (With those guys, it really does not matter, just replace them.)
All of my NR lower races are dimpled now , the longest lasting for 24 years. Tange headsets are pretty nice.
Steven Johnson, Millersville, MD
Date: Mon, 23 Nov 2009 16:32:32 -0500 From: Ken Freeman <kenfreeman096@gmail.com>
Cousin Bob, I didn't mean to say that brinelling doesn't happen. I don't think it happens just from impact, rather I think it happens from long term repetitive grinding between a ball and a spot on a race, when the interface is dry and dirty. If impacts occur to a compromised race surface, I can only imagine it degrades worse.
My main concern was that some newbies (maybe CR is closed enough that this is not likely to happen?) might read something about the possibility of leaving a headset loose, and think it is not right to tighten out the play. I was worried that your comments could be misconstrued in that way, and lead someone astray, contrary to your intent.
I was trying to explain my view that preloading tends to prevent impact between ball and race because they are forced into contact. I think there's a degree of lubricated pressure that will run smooth for a long time and not result in damage from riding over bumps. I don't really have a good picture of what the upper limit of preload looks like. Based on the "hair trigger" behavior of NR's I have owned, not much preload can be stood, since I think it's totally wrong to tighten the bearing into roughness.
I'm not sure I get the point about the '30s roadster. It sounds like it had old hardened grease in it, and it was rough possibly because fo dirt, but certainly because balls were running on hardened clumps of grease. That isn't brinelling, if I understand your story. Presumably it could have lead to brinelling, but I guess I really can't say.
I'm not going to be able to analyze it further, so I'm done. Far be it from me to tell you to do something different in your shop.
That is an interesting theory which is believed by some including the
> venerable Jobst Brandt, who calls it fretting (read his words here:
> http://yarchive.net/
> brinelling because he has tried to dent a headset with a sledge hammer and
> on a concrete surface and couldn't make any dents. Of course, a "dry land"
> test like this can't really simulate real riding conditions, and it doesn't
> prove it can't happen anyway. But anecdotal evidence (over 30 years of
> working in bike shops) say it still happens from preloading. For eight
> years I have been commuting on a 1962 Schwinn Paramount with its original
> Campy Record headset, which of course is properly adjusted, and it has no
> indexing. I don't know the history of it before ten years ago, but it is
> pretty beat up, which would lead me to believe it had not been well
> maintained, and I have not touched it since I first set it up ten years
> ago. It gets ridden in the rain for six months out of the year. Surely
> that is bad enough treatment over a long enough time to have made the
> lubrication failure possible, and yet it is perfectly smooth. Come to think
> of it, my 50s Rudge with original Raleigh headset that I put together in
> 1981 has never been overhauled. It gets regular use around town in all
> weather on errands. No indexing. But I have seen many bikes come in with
> indexed headsets, that have only seen a couple months of use, and were
> perfectly clean. Another anecdote: I used to have a late 30s BSA which I
> got from its original owner. The headset was rather difficult to overhaul
> because the bike had rod-actuated brakes and all that would have to come off
> to do it. I always assumed the headset was toast because it would hardly
> turn. Made the bike very annoying to ride. I finally sold the bike a few
> years ago, and because the buyer was a good friend of mine, I decided to
> overhaul the headset. It was the original TDC, and remarkably, once I got
> all the old hardened grease out of it and relubed and reassembled it, it
> was smooth as butter and I had second thoughts about selling it. That
> certainly doesn't support the lubrication failure theory.
>
> Ironically, Ken seems to say that brinelling *does* happen in his second
> paragraph "This small misalignment tends to focus pressure on a few balls
> and their contact points. It also creates impact contact between ball and
> race." Which is it Ken? Lubrication failure or impact? I have certainly
> seen uneven denting, when the headset was installed slightly out-of-plane.
> That only makes sense, as it is getting more preload in one spot all the
> time. But in many cases, the headset was perfectly square in the frame, and
> the denting was perfectly even around the race.
>
> And by the way, I didn't say I advocate running a headset at all loose. I
> said to adjust it from *loose to not loose*, rather than from* tight to
> not tight* as you can't really feel the preload on a precision headset
> that is perfectly installed but adjusted too tight, so the best you can do
> is start loose and adjust it until you take the slop out of it.
>
> Here are two observations that support the brinelling theory: I have seen
> significantly more headsets go indexing that were alloy headsets
> with pressed-in steel races, like Campy Super Record and 80s era ball
> bearing Dura Ace. The steel races are hardened of course, but they are very
> thin, and the substrate aluminum is softer and allows the balls to indent
> the races easier than an all-steel headset. If fretting were the answer
> then the hardened steel races should wear more slowly, right? And another:
> I have seen it significantly more on racing bikes (that have steeper head
> angles and run higher pressure tires) than on touring bikes (with shallower
> angles and softer tires), and almost never on a mountain bike, where mud
> should make the lubrication failure, if it exists, quite a problem. Perhaps
> fretting does happen, but only when a headset is already starting to brinell
> because it has been overtightened, and the bearings are captured in their
> dents.
>
> I will continue to adjust my headsets carefully and not too tight because
> it has always worked for me. In Seattle we call lubrication failure RUST.
>
> regards
>
> Bob Freeman
> Elliott Bay Bicycles
> 2116 Western Ave
> Seattle, WA 98121
> 206-441-8144
> Home of Davidson Handbuilt Bicycles
>
-- Ken Freeman Ann Arbor, MI USA
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