Paint crack or frame crack?

Quoted message said:

I have a 1995 Cannondale 2.8 series (CAAD3) road frame with about
9,000 miles on it. I just noticed that the paint is cracking on the
drive-side seatstay about 3/4" above where it joins the chainstay,
right at a crease that's bent into the seatstay presumably for cog
clearance. The cracks in the paint are in the shape of a plus sign.

The described circumstance is almost certainly a crack in the frame. It is
possible to have cracks in the paint and not the metal. The only real way to
tell is to remove the paint from the area.
Phil Brown

On 31 Jul 2004 21:54:28 GMT, [email hidden] (Phil Brown)

Quoted message said:

Quoted message said:

I have a 1995 Cannondale 2.8 series (CAAD3) road frame with about
9,000 miles on it. I just noticed that the paint is cracking on the
drive-side seatstay about 3/4" above where it joins the chainstay,
right at a crease that's bent into the seatstay presumably for cog
clearance. The cracks in the paint are in the shape of a plus sign.

The described circumstance is almost certainly a crack in the frame. It is
possible to have cracks in the paint and not the metal. The only real way to
tell is to remove the paint from the area.

I concur about the need to remove the paint to determine if the frame
is cracked, and it would probably be wise to do so. I have seen paint
shrink and crack on interior curves in various applications without an
failure of the underlying material, but in this instance, I believe it
is possible that the paint crack is indicative of a more seious fault,
and I'd say that it's best not to guess.

I don't know if that frame would be under a warranty, but if you
bought the bike new, it would be wise to consult with your local Cdale
dealer before proceeding. Many major-name frames come with a lifetime
warranty for the original purchaser. If yours is one of these, then
letting the dealer look it over before doing anything else may be your
best plan.

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"Werehatrack" wrote: (clip)I have seen paint shrink and crack on interior
curves in various applications without an failure of the underlying
material, but in this instance, I believe it is possible that the paint
crack is indicative of a more seious fault, and I'd say that it's best not
to guess.(clip)
^^^^^^^^^^^^^^^
Long before I retired, when I was working as a mechanical engineer, we used
a product called "Stresscoat." It was a very brittle lacquer, which we
sprayed on a structure--after it was dry, loads were applied, and the stuff
would crack wherever there was tensile stress. It was possible to visualize
areas of high stress, so design decisions could be made. Since bicycle
finishes are quite hard, and aluminum is fairly soft, it is possible that
the finish could crack without an underlying failure of the metal.

HOWEVER, it is also possible that the metal is cracking, causing the finish
to crack with it. I agree with Werehatrack that the only way to find out is
to take off the finish and look--possibly with a magnifier. After the metal
is exposed, it might be useful to rub something dark, like shoe polish, into
the area.

Leo Lichtman said:

"Werehatrack" wrote: (clip)I have seen paint shrink and crack on interior
curves in various applications without an failure of the underlying
material, but in this instance, I believe it is possible that the paint
crack is indicative of a more seious fault, and I'd say that it's best not
to guess.(clip)
^^^^^^^^^^^^^^^
Long before I retired, when I was working as a mechanical engineer, we used
a product called "Stresscoat." It was a very brittle lacquer, which we
sprayed on a structure--after it was dry, loads were applied, and the stuff
would crack wherever there was tensile stress. It was possible to visualize
areas of high stress, so design decisions could be made. Since bicycle
finishes are quite hard, and aluminum is fairly soft, it is possible that
the finish could crack without an underlying failure of the metal.

HOWEVER, it is also possible that the metal is cracking, causing the finish
to crack with it. I agree with Werehatrack that the only way to find out is
to take off the finish and look--possibly with a magnifier. After the metal
is exposed, it might be useful to rub something dark, like shoe polish, into
the area.

Magnaflux Corp used to make a kit for aluminum crack detection which
used a high-capillary dye to penetrate the crack, and a wash and
revealer coat to show where the dye had penetrated. I used to get it
from one of the aviation parts houses, but that was quite a while ago.
Some bearing supply houses also used to carry it. I haven't needed it
in a while, so I've lost track of the current sources.

--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Quoted message said:

I have a 1995 Cannondale 2.8 series (CAAD3) road frame with about
9,000 miles on it.

I have a 2002 R400 Cannondale CAAD3, with paint cracks at the joints of the
seat stays and seat tube. I have 3600 miles on this bike.
It would be of interest to me to know if your
situation is metal crack or paint cracks.

Keith

http://www.mcmaster.com

Page 2118. Quite expensive for a DIY project. You can get good results using the dye made for finding engine oil leaks, dissolved in a light penetrating oil. Remove the paint by sanding, feathering the edge as to not collect the dye. Use 400 grit paper dry for the final polish as rough surfaces hold dye and will increase the background. Clean with laquer thinner or acetone. Apply a thin layer of the dyed oil and let sit for 10 minutes. Wipe off excess with lint free cloth. To develop, make a slurry of fine talcum powder in alcohol. Spray this with a airbrush in thin layers, letting it dry between each coat until the surface is a uniform white color. Make sure to agitate the airbrush to keep the slurry in suspension. Let sit for 10-30 minutes and observe with a UV lamp. Any cracks will show as lines of decreasing thickness.

Leo Lichtman said:

Long before I retired, when I was working as a mechanical engineer, we used
a product called "Stresscoat." It was a very brittle lacquer, which we
sprayed on a structure--after it was dry, loads were applied, and the stuff
would crack wherever there was tensile stress. It was possible to visualize
areas of high stress, so design decisions could be made. Since bicycle
finishes are quite hard, and aluminum is fairly soft, it is possible that
the finish could crack without an underlying failure of the metal.

On a welded frame like the Cannondale, the chances that it is a fatigue
crack are higher than would be the case with a bonded frame. During the
early months after the Trek bonded aluminum frame was introduced, we had
many returns for what appeared to be cracks at the frame joints. These
turned out to be simple paint cracks, presumably because the glue joint
allowed a little more flex than the paint could tolerate.

--

-John ([email hidden])