I really appreciate all the thoughtful comments!
My original question stemmed from the fact that it is not terribly uncommon for me to find some minor flaws in a bicycle bearing cone when I service a wheel, and I find it galling (ahem) to be spending a reasonable amount of money on replacing the cone when I have some metal-working tools within eyeshot. This is particularly true when this is an inexpensive hub on my commuter bike, and as such is subjected to a fair amount of (loving) abuse. This winter was particularly brutal for the poor thing.
After noticing the damaged cone in question, I took apart two other identical spare (used) hubs in search of a guerrilla replacement part, and I found that five of the six cones had similar minor pitting. I'm thinking there might be a number of explanations for this: it might be due to shocks from the wheel transmitted through the bearing, or, if the hub was ever stored with moisture in the bearing and experienced some corrosion, or it's also conceivable that the cones in this specific brand of hub (Joytech) are manufactured from stock where these flaws were included in the material.
In any event, my hope is/was to find some manner of cleaning the ball path to the point where I can eliminate some of the annoying earmarks of a scarred cone (the clicking, the rumble, etc
. The cones are reusable as-is, I'm mostly interested in whether I can make them marginally better at minimal cost.
A .001" surface correction isn't very much, and if you use a very fine grindstone and profile it to match the curvature of the bearing, it could work. If it doesn't work, it doesn't seem like you're out anything since it needed to be replaced anyway. If it works, it's a small victory in one of those "they said it couldn't be done" stories. Best of luck!
I think I'm probably looking at a bit more than a tenth, but I was essentially wondering if what you suggest might be practical. And you're quite correct that the cost of failure (ie, spoiling the part) is relatively small. It would seem to me that the key is to try and match the cone's curvature, as you say.
Since the cone for this type of cup-and-cone bearing has a threaded bore and is screwed into the bearing, if one could take a uniform skim on the inside face of the cone it wouldn't affect the geometry of the bearing at all. The only ramification would be that the cone would lose some width, thus making the over-locknut-distance shorter by perhaps .010", which is trivial for this dimension.
Thing is I have ridden bikes with really bad races and was surprised at how serviceable they were. Not to say that I wanted them that way, they were a bugger to adjust, but I just couldn't justify the cost of making something perfect when it was good enough for my purposes. In my experience with bicycle wheels when wear/rust pitting shows up on the races, the balls are even worse. New balls and grease can make them liveable if not serviceable by definition.
When it comes to Hannes' original question, it depends on the objective of the exercise and on what standards Hannes wants to work to.
I have often wondered about the actual (and required) tolerances of bicycle wheel bearings. My guess is that they are fairly forgiving. Perhaps I'm mistaken (which happens far too frequently), but I'm guessing that the precision of matching the cone's curvature, while not unimportant, is perhaps less critical than ensuring that the curve cross-section is uniform about the axle.
As an aside, as well as the source of some consternation, I'm only talking about the cones in this case. The balls and races/cups seem to be in fine condition.
if it's just a little wear and you're not precious about a little rumble coming from the wheel, then just stuff some fresh grease in it every so often and you'll be fine. I've ridden bikes like that for years without any problems. That said, it's just a cone, buy some new ones! The front hub on my wife's bike was the original Shimano STX hub on my first mountain bike bought in 1996. It's had a new axle, countless wheels built around it and more replacement cones than I can remember over the 10,000+ miles it's done and it still spins beautifully
Generally speaking I quite agree with this sentiment. I was just hoping that perhaps someone might've traveled down this road already.
I have a few cones in my parts bin. Post up a pic and I'll see what I can find.
Is this a front or rear? Brand? Age?
Dan, this is an extremely kind offer -- I truly appreciate it. However, I really don't want to put you out, particularly when I could go down to the LBS and probably find something. I was just hoping that there might be some reasonable approach to apply a homebrew fix.
It depends on the hub you have.
Most likely you'll cut through the hardening and it'll have a really short life. [...] That said, most likely greasing them up and adjusting them properly will probably get you a bunch of life out of it.
I put in many thousands of miles a year, and have kept hubs like that working for quite a while as I tend to wear them out. My next new bike should be here next week, then you wont be able to find me for a while.
This is one of the issues I'm very curious about. If you're right, and the cones are only surface-hardened, then any slightly more aggressive type of remediation on the bearing surface would be a problem. If they are through-hardened, then taking the surface down a bit and re-polishing would potentially seem to be possible.
I agree with your point about repacking the bearing -- I've put a lot of miles on bearings like that, too. But it would be quite cool to be able to refurb them, I think.
Congratulations, and happy trails on your new ride!
Thank you, again, to everyone, for your comments -- I'm very grateful for your time!
Hannes.
