Titanium bearing races report

I'm making this posting to be archived by Google as a data point and for
future reference.

I was doing maintenance on a Dura-Ace WH-7700 wheelset which comes with
a titanium cassette freehub body. The freehub body was replaced, and I
performed an autopsy on the dead freehub body. The wheel had many miles
and wasn't well maintained. The wheel bearings were toasted, and the
freehub body bearings were also very worn and were devoid of their
chromium. The cone pieces of the freehub body made of hardened steel
were severely pitted all the way around on both the inboard and outboard
set. I expected to see cups in the titanium freehub body as severely
worn as the cone pieces & balls, but this was not the case. The titanium
cup races looked absolutely pristine as if there were no wear at all.
There wasn't even a visible line showing the track of the balls within
the cups. They looked new. This is only a single freehub body, but the
implication is that titanium cups & cones or even ball bearings might
offer substantial improvement over steel.

Yikes, I was so impressed with the bearing races that I totally failed
to notice how badly the pawl ratchet surfaces were worn. The wear was
very, very heavy. The steel pawls are narrower than the surfaces they
engage, and the steel pawls wore a deep groove through the titanium. The
height of the ratchet face was reduced by 50% and 6 of the 16 surfaces
also had heavy 45 degree beveling at the edge that further reduced the
height of the ratchet face. The wear was very even, almost appearing as
if it were machined instead of wear. Only the edges had visible ragged
wear under high magnification. It appears that while the bearing
surfaces appear unworn, the ratchet surfaces are horrible. Perhaps
titanium isn't suitable for freehub bodies, but cups & cones still seem
like they'd be improved in titanium.

Kris Tilford wrote:
I was doing maintenance on a Dura-Ace WH-7700 wheelset which comes
with a titanium cassette freehub body. The freehub body was replaced,
and I performed an autopsy on the dead freehub body. The wheel had
many miles and wasn't well maintained. The wheel bearings were
toasted, and the freehub body bearings were also very worn and were
devoid of their chromium. The cone pieces of the freehub body made of
hardened steel were severely pitted all the way around on both the
inboard and outboard set. I expected to see cups in the titanium
freehub body as severely worn as the cone pieces & balls, but this
was not the case. The titanium cup races looked absolutely pristine
as if there were no wear at all. There wasn't even a visible line
showing the track of the balls within the cups. They looked new. This
is only a single freehub body, but the implication is that titanium
cups & cones or even ball bearings might offer substantial
improvement over steel.

It is common to see more wear on cones than cups, even when all parts are
steel.

~PB

"Kris Tilford" wrote in message
...
I'm making this posting to be archived by Google as a data point and for
future reference.

..., but the
implication is that titanium cups & cones or even ball bearings might
offer substantial improvement over steel.

Kris: the freehub body on the Shimano Dura-Ace and XTR rear hubs are indeed
titanium. However, I know as a fact that the stock balls are not ti. They
are stainless steel grade 25 balls. The hub cones are definitely steel.
And I'd bet with 100-1 odds that the cups on both sides are forged steel.

When hubs wear out the balls and the cones usually wear out much faster than
the cups. The cups have much more surface area to take the abuse of
contaminants and lack of lubrication. Given that a Shimano hub overhaul
takes all of 10 minutes, it takes extraordinary degree of neglect to cause a
good hub to lose its cups.

Kris Tilford wrote:
I'm making this posting to be archived by Google as a data point and for
future reference.

I was doing maintenance on a Dura-Ace WH-7700 wheelset which comes with
a titanium cassette freehub body. The freehub body was replaced, and I
performed an autopsy on the dead freehub body. The wheel had many miles
and wasn't well maintained. The wheel bearings were toasted, and the
freehub body bearings were also very worn and were devoid of their
chromium.

ball bearing races are not chromed.

The cone pieces of the freehub body made of hardened steel
were severely pitted all the way around on both the inboard and outboard
set. I expected to see cups in the titanium freehub body as severely
worn as the cone pieces & balls, but this was not the case. The titanium
cup races looked absolutely pristine as if there were no wear at all.

the cups are steel, not titanium. it's common to see cups in reasonable
condition while cones have spalled - it's a function of the loading
geometries between the ball and the race.

There wasn't even a visible line showing the track of the balls within
the cups. They looked new. This is only a single freehub body, but the
implication is that titanium cups & cones or even ball bearings might
offer substantial improvement over steel.

not at all. titanium can't touch steel for hardness in this kind of
application so it is not used for bearings.

next time, make sure the bearings are correctly adjusted. the symptoms
you describe are typical of the bearings being too tight.

On Sun, 26 Jun 2005 15:39:39 GMT "Dave Mayer"
wrote:

Kris: the freehub body on the Shimano Dura-Ace and XTR rear hubs are indeed
titanium. However, I know as a fact that the stock balls are not ti. They
are stainless steel grade 25 balls. The hub cones are definitely steel.
And I'd bet with 100-1 odds that the cups on both sides are forged steel.

I've never seen one of these, but I agree with most of it. Most
bearing balls are made from chromium steel, which is often confused
with stainless steel.

Bearing steels are all magnetic, while titanium is not. A small magnet
would easily convince you that your bearing parts are steel, not
titanium. Titanium wouldn't make good bearing parts, just as in your
other post you discovered that it doesn't make a good ratchet
material.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

On Sun, 26 Jun 2005 00:57:27 -0500, Kris Tilford wrote:

The titanium
cup races looked absolutely pristine as if there were no wear at all.
There wasn't even a visible line showing the track of the balls within
the cups. They looked new. This is only a single freehub body, but the
implication is that titanium cups & cones or even ball bearings might
offer substantial improvement over steel.

It has already been pointed out that the cups were undoubtedly steel, not
titanium. This is part of the mythology of titanium, which certainly
predates its use in bicycles. The belief is that titanium is stronger
than steel and lighter than aluminum, although neither is the case. It
is, in fact, lighter than steel and stronger than aluminum, but not as
strong as steel nor as light (per volume) as aluminum.

--

David L. Johnson

__o | Do not worry about your difficulties in mathematics, I can
_`\(,_ | assure you that mine are all greater. -- A. Einstein
(_)/ (_) |

Kris Tilford wrote:

Yikes, I was so impressed with the bearing races that I totally failed
to notice how badly the pawl ratchet surfaces were worn. The wear was
very, very heavy. The steel pawls are narrower than the surfaces they
engage, and the steel pawls wore a deep groove through the titanium. The
height of the ratchet face was reduced by 50% and 6 of the 16 surfaces
also had heavy 45 degree beveling at the edge that further reduced the
height of the ratchet face. The wear was very even, almost appearing as
if it were machined instead of wear. Only the edges had visible ragged
wear under high magnification. It appears that while the bearing
surfaces appear unworn, the ratchet surfaces are horrible. Perhaps
titanium isn't suitable for freehub bodies, but cups & cones still seem
like they'd be improved in titanium.

Improved? Over steel?? Hardly.

Try filing, drilling, sanding or otherwise working titanium
some time. It is not at all suitable as a bearing surface.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

When I looked up informaton on Ti alloys. It can be as strong as some steels
about 180+ psi tensile strength, but its Young's modulus is worst by about
50% compared to steel. Of course the best steels have higher tensile
strength than the best Ti alloys.

cel


"David L. Johnson" wrote in message
news
On Sun, 26 Jun 2005 00:57:27 -0500, Kris Tilford wrote:

The titanium
cup races looked absolutely pristine as if there were no wear at all.
There wasn't even a visible line showing the track of the balls within
the cups. They looked new. This is only a single freehub body, but the
implication is that titanium cups & cones or even ball bearings might
offer substantial improvement over steel.

It has already been pointed out that the cups were undoubtedly steel, not
titanium. This is part of the mythology of titanium, which certainly
predates its use in bicycles. The belief is that titanium is stronger
than steel and lighter than aluminum, although neither is the case. It
is, in fact, lighter than steel and stronger than aluminum, but not as
strong as steel nor as light (per volume) as aluminum.

--

David L. Johnson

__o | Do not worry about your difficulties in mathematics, I can
_`\(,_ | assure you that mine are all greater. -- A. Einstein
(_)/ (_) |

On Sun, 26 Jun 2005 21:00:14 -0700, cel wrote:

When I looked up informaton on Ti alloys. It can be as strong as some steels
about 180+ psi tensile strength, but its Young's modulus is worst by about
50% compared to steel. Of course the best steels have higher tensile
strength than the best Ti alloys.

And decent bearing cups would be made of high-quality steel.

--

David L. Johnson

__o | Become MicroSoft-free forever. Ask me how.
_`\(,_ |
(_)/ (_) |