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#1
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Paint crack or frame crack?
Does paint on a frame crack by itself, or is that an indication that the frame is cracking or flexing underneath it? 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. In the horizontal direction (inside the seatstay) it runs about 1/2" right in the middle of the indentation. Vertically it runs about 1/4" on the very back edge of the seatstay. The middle of the crack, where the vertical and horizontal cracks meet, is at the most extreme squish point of the indentation, where it meets the regular round part of the seatstay. Seems like a likely stress point. Hope all this makes sense. I tried taking photos of the crack but can't get it to show in the photos (all you see are the bits of paint I've flecked off). Tried a very oblique lighting angle and macro mode on the camera but it doesn't show up in the photos. So, is this an indication that the frame is a goner? I know Cannondale warrants frames for life, but can't find the guarantee on their website. Anyone have experience getting a replacement frame? Thanks, Michael |
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#2
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Paint crack or frame crack?
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 |
#3
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Paint crack or frame crack?
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#4
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Paint crack or frame crack?
"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. |
#5
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Paint crack or frame crack?
On Sun, 01 Aug 2004 02:24:43 GMT, "Leo Lichtman"
wrote: "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. |
#6
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Paint crack or frame crack?
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 |
#7
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Paint crack or frame crack?
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. -- Weisse Luft |
#8
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Paint crack or frame crack?
On 2004-08-01, Leo Lichtman wrote:
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 ) |
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