Re: [CR] Campy NR Headset & Brinelling

From: <RDF1249@aol.com>
Date: Mon, 23 Nov 2009 15:59:29 -0500
To: <kenfreeman096@gmail.com>, <haxixe@gmail.com>
Cc: jefflaw@msn.com, classicrendezvous@bikelist.org
Subject: Re: [CR] Campy NR Headset & Brinelling

kenfreeman096@gmail.com writes:

When I had to repair sand and grit damage in a NR headset I found it very hard to find lower bearing replacement parts that were not brinelled already. I finally did, but there were quite a few made that are now not usable.

I can't agree about too loose being ok at all. The reason to have a bunch of balls is for them to share the load pressure. They will only do this if for both bearings the upper and lower races (or cups and cones) are aligned in plane well-nigh perfectly. If the bearing is loose, then when weight is added, and certainly with transient loads like bumps, the steer tube will move slightly in the head tube. This small misalignment tends to focus pressure on a few balls and their contact points. It also creates impact contact between ball and race. This can be worse than constant contact with varying pressure.

Not only should they be aligned right to eliminate motion, but even with an SP frame there is some miniscule elasticity, which allows the steer tube to flex with bumps. This flex also momentarily takes the bearing pairs out of plane. With just the right amount of preload, contact can be maintained all around the circle of bearing balls much more consistently. I don't have any specs about a preload torque, but I tend to tighten NR headsets until the play disappears, then a touch more, barring any feel of roughness or drag.

I don't think impact is the cause of brinelling. I think, and believe I read in one of Zinn's books, that it's caused by long-term use of a bearing that contains dirt and has gone dry. Dry bearings don't always feel rough. Hardened grease that has lost its suspended oil might have been pushed away from the ball track, resulting in the balls running essentially metal to metal. I think this constant grinding is what damages race surfaces.

On Mon, Nov 23, 2009 at 2:37 AM, Kurt Sperry <_haxixe@gmail.com_ (mailto:haxixe@gmail.com) > wrote:

I have a 1970 bike that I bought used in the early eighties with obviously quite a few miles with what I am reasonably certain is its original C in a diamond NR headset. For around ten years that bike was my only transport and I rode it everywhere piling up many, many thousands of miles including a fair bit of off road duty. It's still my daily rider and I've had the headset apart I think twice in those twenty odd years. All the parts including the bearings are the same ones I bought it with and it still feels fine.

I'm left wondering what the hell you have to do to damage or wear out a properly adjusted NR headset because it seems damn near impossible to me in one lifetime.

Kurt Sperry Bellingham, Washington USA

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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/bike/head_bearing.html ) He rejects the term 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