Lapping Compound for BB races?

Rex Kerr said:

I have a 70s Peugeot fixie that has a rough/noisy bottom bracket that
new bearings didn't improve-- it's ridable, but noisy!

I'd rather not invest the money on a new BB right now {besides, the
french threaded ones are hard to find} so I was wondering what people
think of reinstalling the old bearings with some lapping compound and
riding it a hundred miles or so before overhauling it again. Will I
remove too much material? Will the races be too soft once the surface
has been worn down? Will it be impossible to clean them well enough
that it won't harm the new bearings?

Although abrasives are used to produce the shaped surfaces of many
precision bearings, the manner of their use is not as crude and
uncontrolled as what you propose.

Bearing surfaces so treated would be asymmetric, and contaminated with
abrasive embedded in the surface of the steel. The cups would not be
the only things that would take damage; the shaft would likely get
trashed by asymmetric wear as well. As the wear progressed, the unit
would get sloppier while riding. You might not get 100 miles before
the BB jammed anyway.

Harris Cyclery has just the cups (made by Sugino, but unless you've
got the thin cups, there's a good chance these will work) for $30 plus
shipping. Matching shafts are also available if you've got a BB that
can't be used with these cups.

--
Typoes are a feature, not a bug.
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Werehatrack said:

Bearing surfaces so treated would be asymmetric, and contaminated with
abrasive embedded in the surface of the steel.

The bearings used for this 'expriment' would be the original bearings
that are already headed for the trash bin, new bearings would be
installed once the lapping compound was removed.

Quoted message said:

The cups would not be the only things that would take damage;
the shaft would likely get trashed by asymmetric wear as well.

I was wondering about the spindle. I assume that they're also
hardened, no? I'd expect them to also be smoothed out by the rotating
mixture of lapping compound and bearings.

Quoted message said:

Harris Cyclery has just the cups (made by Sugino, but unless you've
got the thin cups, there's a good chance these will work) for $30 plus
shipping. Matching shafts are also available if you've got a BB that
can't be used with these cups.

Yeah, I saw that after posting, though I'm not sure if I need just the
cups or a new spindle also.

Right now I'm inclined to say that if I'm going to end up tossing the
parts eventually anyway, it might be a cheap experiement worth trying,
especially if I can order replacement parts.

Rex Kerr said:

Werehatrack said:

Bearing surfaces so treated would be asymmetric, and contaminated with
abrasive embedded in the surface of the steel.

The bearings used for this 'expriment' would be the original bearings
that are already headed for the trash bin, new bearings would be
installed once the lapping compound was removed.

The balls are just one part of the bearing. The surfaces that would
take asymmetric wear are those in the cups and on the shaft; both of
those get loaded by side forces that are not constant all the way
around the surface; you'd end up with an uncentered oval in each case.

Quoted message said:

Quoted message said:

The cups would not be the only things that would take damage;
the shaft would likely get trashed by asymmetric wear as well.

I was wondering about the spindle. I assume that they're also
hardened, no? I'd expect them to also be smoothed out by the rotating
mixture of lapping compound and bearings.

Quoted message said:

Harris Cyclery has just the cups (made by Sugino, but unless you've
got the thin cups, there's a good chance these will work) for $30 plus
shipping. Matching shafts are also available if you've got a BB that
can't be used with these cups.

Yeah, I saw that after posting, though I'm not sure if I need just the
cups or a new spindle also.

Right now I'm inclined to say that if I'm going to end up tossing the
parts eventually anyway, it might be a cheap experiement worth trying,
especially if I can order replacement parts.

At present, if the shaft's surfaces are smooth, you might be able to
salvage it. After the lapping, it's unlikely that this would be the
case.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Rex Kerr said:

I have a 70s Peugeot fixie that has a rough/noisy bottom bracket that
new bearings didn't improve-- it's ridable, but noisy!

I'd rather not invest the money on a new BB right now {besides, the
french threaded ones are hard to find} so I was wondering what people
think of reinstalling the old bearings with some lapping compound and
riding it a hundred miles or so before overhauling it again. Will I
remove too much material? Will the races be too soft once the surface
has been worn down? Will it be impossible to clean them well enough
that it won't harm the new bearings?

Thanks!

Is there visible wear on the cups and/or the spindle?

When you are adjusting it, is the choice between "loose with play" or
"no play but rough"?

Rex Kerr said:

I have a 70s Peugeot fixie that has a rough/noisy bottom bracket that
new bearings didn't improve-- it's ridable, but noisy!

I'd rather not invest the money on a new BB right now {besides, the
french threaded ones are hard to find} so I was wondering what people
think of reinstalling the old bearings with some lapping compound and
riding it a hundred miles or so before overhauling it again. Will I
remove too much material? Will the races be too soft once the surface
has been worn down? Will it be impossible to clean them well enough
that it won't harm the new bearings?

Thanks!

don't bother. you'll end up with eccentric races and will be running on
the soft substrate, not the hardened outer layer, what is currently
spalling. just invest in the new cups and be done with the aggravation.

Quoted message said:

When you are adjusting it, is the choice between "loose with play" or
"no play but rough"?

No, it's loose and smooth but noisy or tight and smooth but noisy.
Tightening the cups doesn't seem to affect the noise nor the smoothness
of the rotation. I can spin the cranks (without the chain attached)
and they'll spin for a long time.

Rex Kerr said:

I have a 70s Peugeot fixie that has a rough/noisy bottom bracket that
new bearings didn't improve-- it's ridable, but noisy!

now that everyone has discouraged you completely, I will give you the
information that you requested :

- initial lapping compound : something like automotive rubbing
compound
- final lapping compound : something like brite-white abrasive toothpaste

Use new bearings for the lapping process, and discard bearings when
installing new (or no) compound. I suggest you do the lapping
manually, it will take something like 1-2 hours to do it ( i haven't
done this yet, but have looked into it and asked cyclart about it .)
You will need to tighten up the bottom bracket a lot and work it by
hand. Just "spinning" a loose or optimally adjusted BB won't work.

Some worry warts will complain that you won't have hardened steel
races after you complete the lapping of your bearing. The truth is,
on a low-cost bottom bracket you never had hardened steel races to
begin with, and on a high-cost bottom bracket, they were gone after
20k or 30k miles.

Others have suggested french sugino bottom bracket cups. These will
only work if your existing cups (probably stronglight) match the
thickness of the sugino cups. Another choice might be to purchase
Phil Wood french retaining rings and a UNI-72 or UN-71 bottom bracket
used from ebay, cost would be about $50 total.

- Don Gillies
San Diego, CA, USA

Rex Kerr said:

I have a 70s Peugeot fixie that has a rough/noisy bottom bracket that
new bearings didn't improve-- it's ridable, but noisy!

I'd rather not invest the money on a new BB right now {besides, the
french threaded ones are hard to find} so I was wondering what people
think of reinstalling the old bearings with some lapping compound and
riding it a hundred miles or so before overhauling it again. Will I
remove too much material? Will the races be too soft once the surface
has been worn down? Will it be impossible to clean them well enough
that it won't harm the new bearings?

IIRC, Bicycling! magazine back in the 1970s, once had a little article
on doing approximately what you've suggested, to improve the smoothness
of hub bearings. I believe they described spinning the axle with a
drill, as opposed to merely riding around. They described it as a way
to get the smoothness of high-end Campy in low-end Normandy (or some
such) hubs. Personally, I never tried it. I assume that's why Eddy
Merckx was always a little faster than me. ;-)

The drill technique would remove most of the worry about asymmetric
wear. But have you inspected to see how rough the surfaces are? I
wouldn't count on removing more than a tiny amount of material this
way. Last time I had a low-end BB get rough, the spindle roughness was
too deep to consider using this method.

That reminds me, though - to get a few more miles out of that
particular BB, I installed it in a different orientation w.r.t. the
cranks, hoping that the heavy loads on the balls occurred when the
balls contacted the smooth part of the spindle. I think that if you
just install each crank arm 90 degrees from its current orientation,
that's what you'll have. (Yeah, I should draw the free body diagram to
be sure...)

- Frank Krygowski

Quoted message said:

That reminds me, though - to get a few more miles out of that
particular BB, I installed it in a different orientation w.r.t. the
cranks, hoping that the heavy loads on the balls occurred when the
balls contacted the smooth part of the spindle. I think that if you
just install each crank arm 90 degrees from its current orientation,
that's what you'll have. (Yeah, I should draw the free body diagram to
be sure...)

If the surfaces are rough enough to feel when pedalling, they're most
likely pitted badly enough that lapping would be pointless anyway. If
the pitting is in the axle, however, you've got a good point there; if
the load vector is away from the pitting, then the balls will just
skate noiselessly past them. If the pitting is in the cups, of
course, then there's no rotation to be had on the right side without
installing a shim.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Donald Gillies said:

Another choice might be to purchase
Phil Wood french retaining rings and a UNI-72 or UN-71 bottom bracket
used from ebay, cost would be about $50 total.

This is an interesting idea, but I'm confused... The UN-71 is a
Shimano BB, right? Does it work with the Phil rings? I thought that the
Shimano BB was threaded on the shell (though it's been a while since I
looked at one)

I found the Phil bottom brackets, but they were a bit out of my price
range, but I'd love to be able to use the cheaper Shimano bottom
brackets on this bike!

The UN-71 and UN-72 models are out of production, but still available
on ebay NOS from time to time. On these models, both cups can be
removed to get just a cartridge, making them a more affordable
alternative to Phil wood.

Campagnolo Chorus and Record(i believe) BB's also can have both cups
removed, so these are also good choices for something more affordable
in the short term than a Phil Wood bottom bracket.

- Don Gillies
San Diego, CA

"Donald Gillies" <[email hidden]> a écrit:

Quoted message said:

Campagnolo Chorus and Record(i believe) BB's also can have both
cups removed, so these are also good choices for something more
affordable in the short term than a Phil Wood bottom bracket.

What cups are you suggesting should be used as replacements?

James Thomson

Probably unrelated, since my Huffy uses pound-in soft steel cups, but
you can get extra miles on a worn BB set by rotating the cranks
on the spindle. Do not tighten the BB bearings, however - that
slack is the worn region now on the opposite side of the spindle.

You get, as a result, no wobble when you pedal for another few
thousand miles on the same BB set.

Here's the part that doesn't exactly apply : you don't get to rotate
the cranks 90 degrees and then 270 degrees after using 180 degrees,
because you will have worn through one of the cups entirely, and
the entire BB will self-destruct one day as you're riding, signalling
the end of the BB's life.

I think the screw-in cups probably don't wear through. Also, they're
not as fixed in the BB.

Maybe if I pounded the cups out and reoriented them it would work
better, when I reoriented the cranks.

Anyway, lapping compound will increase that wear, was the triggering
thought.

--
Ron Hardin
[email hidden]

On the internet, nobody knows you're a jerk.

"Rex Kerr" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

I have a 70s Peugeot fixie that has a rough/noisy bottom bracket that
new bearings didn't improve-- it's ridable, but noisy!

I'd rather not invest the money on a new BB right now {besides, the
french threaded ones are hard to find} so I was wondering what people
think of reinstalling the old bearings with some lapping compound and
riding it a hundred miles or so before overhauling it again. Will I
remove too much material? Will the races be too soft once the surface
has been worn down? Will it be impossible to clean them well enough
that it won't harm the new bearings?

Thanks!

What brand and model cranks do you have on your bike. Are they cottered
or cotterless? Many cheap cranksets used BB cups and spindles that were
case hardened only. That is they are hardened to a depth of only .005"
to .050" deep. The metal underneath the case is soft and will wear out
fast. Others were either case hardened or through hardened but not
finish ground after heat treating. These unground cups are always going
to be rough (at least until they are nearly worn out).

I think that the recommendations for lapping applied to bearings that
are not already worn out such as cups and cones/spindles that haven't
been finish ground. Aside from that, the only reason I could see for
lapping worn bearings is in the case of old components where replacement
parts are not available.

A friend came by a bunch of old track bikes from the 1930s. Many of them
had old [censored] size parts. He lapped the bearings on some of them just
to make them partially rideable.

Chas.