How do you repair a cracked carbon seatstay

[yamagold]

The bike suffered a fall and cracked on the seatstay.
Anybody has experience in repairing a cracked carbon seatstay?

I was thinking of filling up the insides with epoxy (Cordobond) making a solid section about 4 inches just above the derailleur hanger.

 

[artmichalek]

Wet sand off the paint/clear coat for about 3 inches on either side of the crack. Use a fine grit sand paper, and don't stop until the surface starts to feel a bit fuzzy. Wrap the stay with 4" carbon tape soaked in epoxy (http://www.shopmaninc.com/) You'll need three to five layers. Once you've got the wet tape in place, wrap the whole thing tightly with plastic wrap and poke a bunch of pin holes in it to let the excess epoxy out. Store the whole bike in a warm location (at least 70F) for at least twice as long as the instructions that come with the epoxy say to. Take off the plastic wrap, sand, paint, and you're good to go. This fix won't be pretty, and it won't be light, but it will be strong.

 

[yamagold]

Good day artmichalek and thanks for the reply.

I went to the website already and checked what they have.
Which epoxy resin did you use? the 635 or the 150? Can the fabric width be cut or do you have to use the whole width. How many layers did you applied and how thick did the final repair come out?

How did you find the strength of the repair. Was it reliable enough to trust the bike say close to the original?

Has anyone tried drilling a hole on the stay and filling up the hollow insides thus making it as one solid stay and leaving a less ugly sight on the outside. at least say about 1 inch extending over the crack?

 

[artmichalek]

Good day artmichalek and thanks for the reply.

I went to the website already and checked what they have.
Which epoxy resin did you use? the 635 or the 150? Can the fabric width be cut or do you have to use the whole width. How many layers did you applied and how thick did the final repair come out?

How did you find the strength of the repair. Was it reliable enough to trust the bike say close to the original?

Has anyone tried drilling a hole on the stay and filling up the hollow insides thus making it as one solid stay and leaving a less ugly sight on the outside. at least say about 1 inch extending over the crack?

I haven't used this technique on a chain stay, so I'm guessing about the strength. You can cut cloth to any size/shape you want. I recomended tape to minimize the amount of fraying. The 635 epoxy is made for use with cloth, the 150 isn't. I wouldn't recomend trying to fill the chain stay with epoxy. Epoxy is very brittle when it doesn't have any reinforcement. Also, when you try to fill up a large volume with it, there's a risk of building up too much heat and having the epoxy crack while it's drying.

 

[yamagold]

I haven't used this technique on a chain stay, so I'm guessing about the strength. You can cut cloth to any size/shape you want. I recomended tape to minimize the amount of fraying. The 635 epoxy is made for use with cloth, the 150 isn't. I wouldn't recomend trying to fill the chain stay with epoxy. Epoxy is very brittle when it doesn't have any reinforcement. Also, when you try to fill up a large volume with it, there's a risk of building up too much heat and having the epoxy crack while it's drying.

THANKS AGAIN FOR THE INFORMATION. WITHOUT THIS FORUM AND KNOWLEGEABLE GUYS LIKE YOU, I COULD HAVE DONE MORE DAMAGE THAN GOOD ON MY ORIGINAL REPAIR INTENTION.

FINALLY HOW DO YOU APPLY THE CARBON TAPE? I ASSUME THE TAPE BE CUT TO THE DIAMETER OF THE STAY AND ALLOW A SLIGHT OVERLAP, APPLY EPOXY, ALLOW TO CURE THEN REAPPLY AGAIN. SOMEWHAT LIKE DOING A ONE ALL AROUND PATCH.
OR DO YOU WIND THE TAPE OVERLAPPING ON THE SIDES LIKE THAT OF WINDING AN ELECTRICAL TAPE. THE FORMER WOULD REQUIRE A TAPE THE WIDTH OF THE INTENDED COVERAGE LENGTH WHILE THE FORMER DOESNT.

 

[dabac]

FINALLY HOW DO YOU APPLY THE CARBON TAPE? I ASSUME THE TAPE BE CUT TO THE DIAMETER OF THE STAY AND ALLOW A SLIGHT OVERLAP, .

I wouldn't do that. For maximum strength you want each fiber to be able to bond to as many other fibers as possible, and with only a short overlap the fibers at the joint won't have much to hold on to.
Rule of thumb for a "full strength" fibreglass repair is to overlap 10x the thickness of the laminate or at least 2 inch.

APPLY EPOXY, ALLOW TO CURE THEN REAPPLY AGAIN. SOMEWHAT LIKE DOING A ONE ALL AROUND PATCH. .

I wouldn't do that. The trick to a weight effective repair is to have as much fiber as possible in as little resin as possible while maintaining full saturation. Allowing to cure between layers will defeat that purpose. Better to work wet-in-wet.
OR DO YOU WIND THE TAPE OVERLAPPING ON THE SIDES LIKE THAT OF WINDING AN ELECTRICAL TAPE. THE FORMER WOULD REQUIRE A TAPE THE WIDTH OF THE INTENDED COVERAGE LENGTH WHILE THE FORMER DOESNT.[/QUOTE] Even if I found a tape with the correct width I wouldn't do it quite like that, because the sudden step from one thickness to another will act as a stress concentrator and might cause trouble further on. You want smooth transitions. If fraying is a manageable issue I might cut a slightly tapered section and wrap it on allowing a nice incremental build-up of thickness. More probably I'd use a narrower tape and wrap the damaged area pretty much like you'd wrap the handle of a tennis racket or similar, but with more overlap. Depending on the orientation and severity of the crack I might put a few strips on lengthwise as well before wrapping it up.

 

[yamagold]

I wouldn't do that. For maximum strength you want each fiber to be able to bond to as many other fibers as possible, and with only a short overlap the fibers at the joint won't have much to hold on to.
Rule of thumb for a "full strength" fibreglass repair is to overlap 10x the thickness of the laminate or at least 2 inch.


I wouldn't do that. The trick to a weight effective repair is to have as much fiber as possible in as little resin as possible while maintaining full saturation. Allowing to cure between layers will defeat that purpose. Better to work wet-in-wet.
OR DO YOU WIND THE TAPE OVERLAPPING ON THE SIDES LIKE THAT OF WINDING AN ELECTRICAL TAPE. THE FORMER WOULD REQUIRE A TAPE THE WIDTH OF THE INTENDED COVERAGE LENGTH WHILE THE FORMER DOESNT.

Even if I found a tape with the correct width I wouldn't do it quite like that, because the sudden step from one thickness to another will act as a stress concentrator and might cause trouble further on. You want smooth transitions. If fraying is a manageable issue I might cut a slightly tapered section and wrap it on allowing a nice incremental build-up of thickness. More probably I'd use a narrower tape and wrap the damaged area pretty much like you'd wrap the handle of a tennis racket or similar, but with more overlap. Depending on the orientation and severity of the crack I might put a few strips on lengthwise as well before wrapping it up.[/QUOTE]
GOOD DAY DABAC AND THANKS FOR YOUR INPUT.
I MISREAD ARTMICHALEK'S 1ST POST AND INDEED HIS SUGGESTION IS THE SAME AS YOURS THAT THE OVERLAPS SHOULD BE A CONTINUOUS ONE.

YES I CAN SEE NOW THE POINT OF ALLOWING INCREMENTAL BUILD-UP OF THICKNESS. I MAY HAVE TO DO THE TAPERED REPAIR WITH PROBABLY 3-4 OVERLAPS (MAYBE MORE IF THE THICKNESS IS NOT TOO UGLY).

 

[yamagold]

I have finally made the repair on the broken seatstay and herewith are the photos during the process of the repair.

I have ridden the bike for about 200 kms now and im happy with the ride and the repair seems to hold. After 2 coats of laminate, the final topcoat/clearcoat will follow after a close up inspection after another 300 kms of riding.

My many thanks to those who have made comments/advices.

Special thanks goes to my mentor/adviser forum member "dabac" who unselfishly shared his knowledge and took the time to answer all my im inquiries.

http://i33.photobucket.com/albums/d87/icelander44/DSCN3167_1.jpg
clearcoat and top laminate removed by wetsanding using 800 grit sandpaper.

http://i33.photobucket.com/albums/d87/icelander44/DSCN3175.jpg
90 deg carbon fiber laid out along the stay length.

http://i33.photobucket.com/albums/d87/icelander44/DSCN3177.jpg
axial lay along the length can be seen on the left of the stay. 90 deg lay can be seen in the center.

http://i33.photobucket.com/albums/d87/icelander44/DSCN3178.jpg
the 0 deg and 90 deg overlay would i think been enough and will almost be an invisible repair. But i opted for a stronger repair by doing a 4 layer overlay. Thickness built up has to be incremental hence a tapered cloth was used.

http://i33.photobucket.com/albums/d87/icelander44/DSCN3179.jpg
After applying the overlay, to avoid an epoxy-rich repair, an inverted electrical tape was wound around the lay to remove excess resin.

http://i33.photobucket.com/albums/d87/icelander44/DSCN3180.jpg
Excess resin oozing out of the needle-pricked tape winding.

http://i33.photobucket.com/albums/d87/icelander44/DSCN3192.jpg
Once the resin has completely cured, tape winding was removed and 2 coats of laminate was applied. Final clearcoat will be applied after another 300 kms of riding after a thorough close-up inspection.

Materials used: TC0200 3k 2x2 CF twill, 105 WS Resin, 206 WS hardener.

 

[John M]

I have finally made the repair on the broken seatstay and herewith are the photos during the process of the repair.

I have ridden the bike for about 200 kms now and im happy with the ride and the repair seems to hold. After 2 coats of laminate, the final topcoat/clearcoat will follow after a close up inspection after another 300 kms of riding.

My many thanks to those who have made comments/advices.

Special thanks goes to my mentor/adviser forum member "dabac" who unselfishly shared his knowledge and took the time to answer all my im inquiries.

http://i33.photobucket.com/albums/d87/icelander44/DSCN3167_1.jpg
clearcoat and top laminate removed by wetsanding using 800 grit sandpaper.

http://i33.photobucket.com/albums/d87/icelander44/DSCN3175.jpg
90 deg carbon fiber laid out along the stay length.

http://i33.photobucket.com/albums/d87/icelander44/DSCN3177.jpg
axial lay along the length can be seen on the left of the stay. 90 deg lay can be seen in the center.

http://i33.photobucket.com/albums/d87/icelander44/DSCN3178.jpg
the 0 deg and 90 deg overlay would i think been enough and will almost be an invisible repair. But i opted for a stronger repair by doing a 4 layer overlay. Thickness built up has to be incremental hence a tapered cloth was used.

http://i33.photobucket.com/albums/d87/icelander44/DSCN3179.jpg
After applying the overlay, to avoid an epoxy-rich repair, an inverted electrical tape was wound around the lay to remove excess resin.

http://i33.photobucket.com/albums/d87/icelander44/DSCN3180.jpg
Excess resin oozing out of the needle-pricked tape winding.

http://i33.photobucket.com/albums/d87/icelander44/DSCN3192.jpg
Once the resin has completely cured, tape winding was removed and 2 coats of laminate was applied. Final clearcoat will be applied after another 300 kms of riding after a thorough close-up inspection.

Materials used: TC0200 3k 2x2 CF twill, 105 WS Resin, 206 WS hardener.

That looks pretty good!! I doubt that I would have even tried such a thing.

 

[yamagold]

That looks pretty good!! I doubt that I would have even tried such a thing.

Thanks John M.
I dont have much choice, otherwise i'll be bikeless for over a month as my crash replacement frameset will have to cross oceans.

These has opened my eyes to the world of carbon fbers. Now i'm thinking of making a carbon fiber deraillieur cage to lighten up somehow.