So I was in the library, and happened to notice some books about bicycles, among which I saw a book of tips from Bicycling Magazine. I glanced through it, and one tip caught my eye: Pack less polished bearings with old balls and metal polishing compound to improve them.

Has anyone ever tried this? And would it work to remove slight damage to old races, or only to improve the smoothness of undamaged races?

If the damage is pitting or deep scratches, that type of polishing won't remove it. If the bearing surface is just a bit rough from crude manufacturing, polishing it will improve the surface.

Unless you have VERY high priced machines to polish bearing to the same size and the races to the right specs, this is a bad idea.

New bearings are not that expensive.

I believe the OP is asking about polishing the races, not the bearing balls. The balls used in the polishing process will be discarded and replaced with new ones. Unless he uses a very coarse polishing compound he will not change the dimensions.

hill

Bearings are manuf to tolerences to fractions of one ten thousands of an inch. What do you propose to "polish" them with?

Sounds like folklore to me. Assuming a brand new piece, normal use (and proper adjustment) smooths out a cheaply manufactured bearing; I doubt polishing compound does a better job.

It seems vanishingly unlikely that the grinding and polishing would start simultaneously all the way around the race - and then stay even for the duration. I would expect it to start in one area and then continue in that area more and more, putting the race out of round.

This would be annoying and a minor disaster - so it will happen. You know it will.

You are free to waste your time as you see fit......

Cup-and cone bearings are user adjustable to maintain what ever tolerance you desire. Polishing the races with a fine abrasive will not change the tolerance you can achieve. I wasn't recommending the use of beach sand as the abrasive.

If the bearings are new and you feel better doing that go ahead - just be advised that it will have no significant effect on your speed or ease of riding. If the bearings are used then the problem that caused the roughness will not go away from polishing.

This is something you might do for a collectible bike you want to make feel nicer, but is useless and even counterproductive for any bike you ride regularly.

There are two main reasons.

1- the steel is much harder at the surface, and on better parts will be hard chrome plated. Polishing removes the hard surface layer, and if carried to excess will lead to rapid pitting. Think of the ice on a frozen lake. When it's thick enough you can skate on it forever. However if it's thin, your weight will depress it into the water causing stress cracks and possibly allowing you to fall through. This is why when bearing races worn beyond a certain point have the characteristic pitting and gouges where there's the most wear, rather than a smooth wear track.

2- Bearing races have a broader curvature than the balls that ride on them. That's so the balls ride with only point contact at their diameter. If you use the same size ball to lap the bearing track, you'll get a groove with the same curvature as the balls. That means that the balls will ride touching along an arced line. So the balls are simultaneously touching at different diameters, and as they roll some sliding has to happen. Sliding isn't rolling, so you get more friction and wear.

This "use the balls and lapping compound" remedy comes around every so often, and some have used it to save collectible hubs or BBs, which it can do very nicely, but it isn't at all suited for a bike you ride more than occasionally.

so would it make sense then
to install oversized balls and polishing compound
for a short time to polish the cup and cone
then clean it all out and reinstall with correct balls and grease
and toss the oversized balls

The larger balls won't sit in the same position on the cone, so will only have an effect on the cup. In fact they could end up on the edge of the cone. They will also push the cone further out on the axle, which could cause problems with having enough axle protruding as well as more difficult mounting between dropouts. Finally, the larger balls will not fit into the groove already made by the smaller ones if it's a used bearing. If the bearings are in bad shape it's best to replace the part, with the exception noted by FB. If it's a new hub just ride it. If well adjusted the difference is not worth worrying about.

This method of "resurfacing" bearing races by using BB's along with an abrasive grinding/polishing compound comes up now and again.

The problem with this method, which will be obvious if you think about it, is in the convex curvature of the BB's and the concave race surfaces. With ideal geometry the two should mate perfectly where they contact each other, and the contact should be more than at a point. Practically, however, BB's contact their races at over limited areas. That is why BB races tend to develop wear grooves over time. Other bearing types (like cylindrical spindle/needle bearings mated to straight tapered races...like the type used for automobile wheels) have less of this problem (though they have other problems for bicycle wheels, mainly greater rolling friction). Because of this BB/race geometry, it will be very difficult to properly "resurface" badly worn BB bicycle races using the BB/abrasive method. The same applies to BB/crank races.

The best solution is to install new ball bearings and races, if possible. That being said, I have used this method to rescue some mildly corroded/worn hubs for which replacement wasn't possible.

In the day , track racers used valve grinding compound and old bearings with a drill to improve hubs , repack using precision balls and then washing out grease with a light oil . adjust cones a little loose and you have a fast wheel . In the day , if you have time .

Not disputing that some did this, but it was bad practice. Lapping in a cheap hub's bearing might help, but decent hubs were already too good to benefit. Replacing grease with oil lowers parasitic drag caused by grease's viscosity, and is fine for the track and road races in dry weather, though it shortens the service interval.

This brings us to the third item, running bearings loose. While it helps an unloaded hub spin better, it actually increases friction in real world conditions. Then hubs that allow user service use angular contact bearings. When loose the bearing surfaces and balls are not in constant contact all the way around. This allows the axle to push itself up between adjacent balls at 12 o'clock driving the balls around and into each other where they rub as they spin in opposite directions. The lowest friction mode for an angular ball bearing is at the minimum preload which ensures zero play. Slightly tight has lower friction than slightly loose.

Legends , of the wooden track , Vancouver B.C. had a old track , outdoor . That was where I heard of it . Suntour Superbe Pro 's had a model that if you messed up a cone or race you could convert to sealed cartridge bearngs . Practical !

Yes, folks did similar things on the east coast.

Bicycle racing, like most sports, is loaded with superstition and voodoo practices. We could start a new thread detailing the various useless and/or counterproductive thins that folks have done to make bikes faster over the years. Many of these come into and out of vogue every 20-25 years or so.