Repairing pitted cones with valve grinding compound
01-22-13, 11:21 AM
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Rubberized-compound grinding wheels can be found at jeweler's supply stores (google "Rio Grande"). They'll cut a lot more slowly than your typical hard abrasive wheel.
01-22-13, 11:27 AM
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BTW- however the grinding is done, once the shape is produced. You can switch to cloth wheels and various grits of polishing compound, ie, white diamond, tripoli and rouge, to bring up a mirror finish. This removes very little metal, so if you continue with the spin grinding method, you'll get a like new cone (except for the issue of material hardness).
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Last edited by FBinNY; 01-22-13 at 11:49 AM.
01-22-13, 11:58 AM
#28
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I bought an old Francesco Moser bike with Gipiemme hubs and all was in great shape except the rear hubs which had significant pitting in the cones. I was going to buy another older Gipiemme hub and cannibalize the cones but the mechanic at my LBS (which is an old school pro in his 60's made an unexpected suggestion. He said "in the old days we used to pack the bearings with valve grinding compound instead of grease and work the bearings back and forth until we ground smooth custom seats inside, then cleaned it really well and reassembled it with grease. Now, I had three thoughts on this: (1) Is this why he never made it into the record books; (2) will it work; and (3) really, what have I got to lose as the hub as it is toast anyway. So I gave it a shot, first with 350 grit and it was going really slow as the seats are really hard. So I used a drill to speed things up and switched to finer and finer grits until I finished with some 80,000 grit that left a nice shinny polish. Then I replaced the balls with new ones and reassembled. I cannit say good as new, but WAY better than what it was. Has anyone heard of doing this?
On the more engineering side; if have access to the right tools, could machine out the old races on a lathe and press in replacments made of the correct type and hardness of material. Making the cones to match would be the easier half of the job.
01-23-13, 10:49 PM
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01-24-13, 08:11 PM
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01-25-13, 05:09 PM
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01-26-13, 10:30 PM
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01-30-13, 01:39 AM
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That's what I was thinking! The OP said that his hub races were ok. Usually it's pitted hub races that are the problem,
and a rather difficult one to fix. Bad cones are much easier to find and replace. Using grease-grit in such a situation risks
damaging perfectly fine hub races...So I'd go with finding some new or good used complementary cones and intalling new
bearings. That makes much better sense to me. Of course if the hub races are shot, you might as well try the grease-grit
technique...or just trash the hub and rebuild with a new hub or just get a new wheel.
and a rather difficult one to fix. Bad cones are much easier to find and replace. Using grease-grit in such a situation risks
damaging perfectly fine hub races...So I'd go with finding some new or good used complementary cones and intalling new
bearings. That makes much better sense to me. Of course if the hub races are shot, you might as well try the grease-grit
technique...or just trash the hub and rebuild with a new hub or just get a new wheel.
10-12-13, 07:00 PM
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Hey just a quick recap. I got about a season of riding on the Gippiem hubs after I resurfaced the cones and no problems or unusual wars noticed afterwards. Apparently I did not go through the hardened surface. This worked like a charm.
10-12-13, 08:42 PM
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10-14-13, 06:41 PM
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I have not opened up but all still rolling smoothly and no additional play developed. I probably will repack over the winter and may post some pictures then.
10-15-13, 12:12 AM
#37
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I work in a bike shop. We can't GET replacement cones for half the hubs out there... if you have a source, can you please share?
My favourite technique for tired bearing surfaces is smoothing them with a Dremel - starting with the round, fine grit heads (the red ones), then the blue polishing ones, then a felt head with rouge or green polishing compound. I keep the speed down so as to avoid excess heat. It's worked pretty well so far - I can't get the really deep pits out but the smaller burring is easy to deal with. I'd like to try it on an indexed headset just for fun.
I was trained by one of those old-school crazy guys and I also have a background in jewellery making, so I'm comfortable with some of the small-scale finicky metalwork that the other guys in my shop won't touch. My other special trick is using a jeweller's anvil, ring mandrel, and very tiny hammers to reshape bent hub dust seals (those stupid metal ones that bend when you look at them sideways and that you can never ever get replacements for...)
My favourite technique for tired bearing surfaces is smoothing them with a Dremel - starting with the round, fine grit heads (the red ones), then the blue polishing ones, then a felt head with rouge or green polishing compound. I keep the speed down so as to avoid excess heat. It's worked pretty well so far - I can't get the really deep pits out but the smaller burring is easy to deal with. I'd like to try it on an indexed headset just for fun.
I was trained by one of those old-school crazy guys and I also have a background in jewellery making, so I'm comfortable with some of the small-scale finicky metalwork that the other guys in my shop won't touch. My other special trick is using a jeweller's anvil, ring mandrel, and very tiny hammers to reshape bent hub dust seals (those stupid metal ones that bend when you look at them sideways and that you can never ever get replacements for...)
10-15-13, 01:20 AM
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Pull the axle, insert plier, widen jaws of plier until they hook on to the dust seal at 180 deg separation. With an appropriately sized hammer, tap tool upwards. So far it's worked beautifully every time.
02-23-14, 09:14 PM
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Hey, just a follow-up because this was mentioned in another thread today. I have a few thousand miles on this hub now and it is rolling as well as my other Gipiemme hub that was not ground. No unusual wear has developed and the hub rolls really well. I do not know if this hub will go another 20,000 miles but I certainly have put a few thousand on with no trouble. This is a good cheap fix if the cone pits are not too deep and if the cones are hard to replace.
02-26-14, 12:06 PM
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It depends on the depth of the pitting, because as was pointed out earlier the steel below the surface is softer than the skin.
But there's a more serious issue, and that's the radius of curvature of the cup and cone.
As produced the curvatures are both greater than that of the balls, so they roll with point contact. If you use the same size balls to lap and you use to run, you'll form grooves with curvatures exactly like that of the balls. That means that the contact area will be wider increasing the friction, but more importantly there'll be contact at various radii. That means that whenever the balls run, there' be some rolling and some sliding contact. This increases friction and the wear rate.
So the lapping trick may be OK for shallow pitting, or as a quick patch for a bearing you plan to replace soon, or to save a collectible and make it workable with the understanding that it won't see much use.
But there's a more serious issue, and that's the radius of curvature of the cup and cone.
As produced the curvatures are both greater than that of the balls, so they roll with point contact. If you use the same size balls to lap and you use to run, you'll form grooves with curvatures exactly like that of the balls. That means that the contact area will be wider increasing the friction, but more importantly there'll be contact at various radii. That means that whenever the balls run, there' be some rolling and some sliding contact. This increases friction and the wear rate.
So the lapping trick may be OK for shallow pitting, or as a quick patch for a bearing you plan to replace soon, or to save a collectible and make it workable with the understanding that it won't see much use.
02-26-14, 12:14 PM
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I've done similar resurfacing on cones, but do it completely differently. I wrap emery of the desired grit around a dowel of the right curvature to make a "sanding stick" then mount the cone on an axle and chuck into a drill press, lathe or power drill held steady. Then spin the cone at high speed, and work the sanding stick up and down with gentle pressure. This lets me remove material fairly quickly and maintain a larger radius curve than the balls. Moving to progressively finer grit, and finally to crocus cloth gives me a decent finish, with concentric patina. The balls finish it off when in use.
I doesn't solve the issues of the case depth or case to core ratio, but does yield a cone on which the ball will roll with tangent vs. secant contact.
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An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
Last edited by FBinNY; 02-26-14 at 12:36 PM.
03-02-15, 08:11 PM
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Just a followup - This hub has roughly 2,500 miles on it now and still is running just fine...
03-03-15, 06:18 AM
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No, because the cup constrains the options too much. Larger balls won't fit between the cup ID and cone OD and track in the desired area (if they fit at all).
I've done similar resurfacing on cones, but do it completely differently. I wrap emery of the desired grit around a dowel of the right curvature to make a "sanding stick" then mount the cone on an axle and chuck into a drill press, lathe or power drill held steady. Then spin the cone at high speed, and work the sanding stick up and down with gentle pressure. This lets me remove material fairly quickly and maintain a larger radius curve than the balls. Moving to progressively finer grit, and finally to crocus cloth gives me a decent finish, with concentric patina. The balls finish it off when in use.
I doesn't solve the issues of the case depth or case to core ratio, but does yield a cone on which the ball will roll with tangent vs. secant contact.
I've done similar resurfacing on cones, but do it completely differently. I wrap emery of the desired grit around a dowel of the right curvature to make a "sanding stick" then mount the cone on an axle and chuck into a drill press, lathe or power drill held steady. Then spin the cone at high speed, and work the sanding stick up and down with gentle pressure. This lets me remove material fairly quickly and maintain a larger radius curve than the balls. Moving to progressively finer grit, and finally to crocus cloth gives me a decent finish, with concentric patina. The balls finish it off when in use.
I doesn't solve the issues of the case depth or case to core ratio, but does yield a cone on which the ball will roll with tangent vs. secant contact.
Just a small safety note here fro those who might try this a home, work on the side of the cone that is going AWAY from you so that if something grabs, it throws it AWAY from you, not INTO you.
I wonder if it might be worth while to talk to a small machine shop or even a hobbyist about having some of these 'unobtainium' cones made out of good steel and hardened. A hobbyist with a lathe and a knife maker with a furnace might be a killer combo.
03-05-15, 07:50 AM
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As a side note. We mechanics do not use grinding compound on modern engines. It ruins multi angle grinds and is a waste of time.
However it is of some use in old lawn mower engines.
Using it on cones? Personally I think its a waste of time and effort. Put the cone on a lathe and spin it down. And hope you stay above the surface hardening.
However it is of some use in old lawn mower engines.
Using it on cones? Personally I think its a waste of time and effort. Put the cone on a lathe and spin it down. And hope you stay above the surface hardening.
03-05-15, 07:40 PM
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I find it easier to work on the "coming" side. There's no real safety issue because it's only sand paper or emery cloth so not very grabby. At the same time, a wooden dowel rod doesn't weigh enough to injure.
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Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
03-05-15, 07:56 PM
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You know how to work around shop tools and not get injured, so do I. I posted that for those who are less experienced and might not think to "think things through" about how they might get injured.
