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PostPosted: Mon May 15, 2017 6:34 pm 
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Joined: Sun Mar 02, 2014 6:36 pm
Posts: 351
Location: NY USA
I have a nice Trek Madone 7.9. The seatstay has been cracked. Short story, it was my own fault with a chain that was too short, when I put on a larger cassette. The chain would just reach if you go big-ring/big-cog. I stay out of that gear. I lent the bike to a mate. I didn't even think about the problem.

Result: derailleur hangar snapped, derailleur caught in spokes, came around and smacked the seatstay. The bike didn't go down (verry low speed incident), but the stay is snapped.

This thread is not a debate of whether to fix it (or get it fixed), it's about what I am doing to fix it myself. Feel free to chime in and tell me I'm looney.

I'm rescuing the frame from the bin, and will learn some skills in the process.

Pics and story to follow.


Here is a "before" pic. It's plain to see the setup was my own fault. I took this picture last year, after building the bike up. I didn't intend to run a 32 in back, but it was possible. But it wasn't possible to cross-chain. :oops:

Quote:
Image


Here is my shopping list for this repair so far (just under $60 USD):

Hanger: http://wheelsmfg.com/derailleur-hanger-176.html
Jockey Wheels: http://www.ebay.com/itm/CNC-Aluminium-J ... 1384026130
Epoxy resin: https://www.amazon.com/gp/product/B0181MDH30
Carbon fiber fabric: (ordered unidirectional, received 2x2 twill): http://www.amazon.com/gp/product/B01DRLC5FG
Carbon fiber fabric: (plain weave. I'm very happy with this stuff) http://www.ebay.com/itm/112387583046

I'll need a new rear derailleur cable, too.

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Trek Madone 7.9 58cm 14.9lbs


Last edited by BikeAnon on Wed May 17, 2017 4:59 pm, edited 1 time in total.

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Posted: Mon May 15, 2017 6:34 pm 


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PostPosted: Mon May 15, 2017 6:50 pm 
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Joined: Sun Mar 02, 2014 6:36 pm
Posts: 351
Location: NY USA
Some pics of the "problem area". The break is visible on only the inside three sides (though you know the whole are is compromised).

The blue tape on the non-problem-side will help us keep track of where the original break is, as we go through the process.

Quote:
Image
Image
Image
Image


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Trek Madone 7.9 58cm 14.9lbs


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PostPosted: Mon May 15, 2017 7:51 pm 
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Joined: Sun Mar 02, 2014 6:36 pm
Posts: 351
Location: NY USA
Here is what it looks like, with the paint removed, and a couple of coats of the uni-directioanl CF sanded through.

This is all new to me. I sanded through the paint, and wasn't eactly sure when I was into just the carbon-fiber. I sopped sanding here. I am not removing the cracked area. I am using the original tube as the "form" for my repair. The repair won't depend on any strength from the cracked area, once it has cured.

I'm confident the repair will be stronger than the original. This will introduce separate issues. Such as:
- Will the patch be so stiff, it creates a lever against where the repair ends (creating a weak spot in the transition area)?
- Will the ride be affected?
- Will the bike weigh more than 15 lbs, when complete (hey, this is WW! :wink: )?

Quote:
Image
Image


the area is now sanded with 100 grit paper, ready for what comes next.

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Trek Madone 7.9 58cm 14.9lbs


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PostPosted: Mon May 15, 2017 7:56 pm 
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Joined: Wed Jan 22, 2014 11:48 am
Posts: 2097
Location: Vienna Austria
Cool, looking forward to the next posts!


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PostPosted: Mon May 15, 2017 8:20 pm 
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Joined: Sat Oct 15, 2016 9:08 pm
Posts: 143
Perhaps you already know this, but you can use heat shrink tape to compress the carbon fiber layup, so it squeezes excess epoxy out and you get higher fiber-to-epoxy ratio, or higher strength-to-weight ratio.

Also, with regards to the transition area acting as a lever: perhaps, instead of having the transition area being vertical (as I think is the current case based on the picture), make it diagonal. The chainstay should flex up/down (normally), so having it diagonal spreads the load between the new and current fibers.


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PostPosted: Mon May 15, 2017 11:12 pm 
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Joined: Sun Mar 16, 2014 3:43 pm
Posts: 777
BikeAnon wrote:

. . . . will learn some skills in the process.


The uk shop easycomposites has a forum Talk Composites
where you can find info.

http://www.easycomposites.co.uk

http://www.talkcomposites.com


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PostPosted: Tue May 16, 2017 12:52 am 
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Joined: Sun Mar 02, 2014 6:36 pm
Posts: 351
Location: NY USA
Thanks. Since this was my first time with carbon-fiber, I decided to do a test run.

Some CPVC pipe I had lying around:
Image

Plain weave carbon fiber fabric. Supplies.
Image

I'm laying out the fabric on plastic, applying the resin, then rolling it out, so the fabric isn't too resin-heavy.
Image
Image

This makes for very clean-cut edges, and I hope will reduce fraying. I'm obviously not focusing on picture-taking skills, although it turns out the pot-life of this resin is over 30 minutes.
Image

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Trek Madone 7.9 58cm 14.9lbs


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PostPosted: Tue May 16, 2017 1:04 am 
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Joined: Sun Mar 02, 2014 6:36 pm
Posts: 351
Location: NY USA
I wrap it up. The edges do fray, but not horrible. At least I don't get long stringy pullouts.

Image
Image

That electrical tape is staged for what comes next.... Wrap tightly, poke hoes with a thumbtack, and allow the resin to ooze out. It's not heat-shrink, but it does give the resin somewhere to go.

While wrapping, I went slowly, giving the bulk of the resin time to work away from each successive wrap.

Image

Once this had oozed a while, I wrapped the whole thing in a couple layers of shop-towel, and gave another tight-stretched wrap of electric tape. I don't know if I have a picture of that step.

This was my home-brew replacement for proper peel-ply, bleeder layer and vacuum bagging.

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Trek Madone 7.9 58cm 14.9lbs


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PostPosted: Tue May 16, 2017 1:05 am 
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Joined: Sun Mar 02, 2014 6:36 pm
Posts: 351
Location: NY USA
antonioiglesius wrote:
....Also, with regards to the transition area acting as a lever: perhaps, instead of having the transition area being vertical (as I think is the current case based on the picture), make it diagonal. The chainstay should flex up/down (normally), so having it diagonal spreads the load between the new and current fibers.
This is an excellent suggestion. Thanks!

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Trek Madone 7.9 58cm 14.9lbs


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PostPosted: Tue May 16, 2017 1:11 am 
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Joined: Wed May 13, 2015 10:35 pm
Posts: 103
Don't know if you have done this but I have found that wrapping the electrical tape sticky side out helps when removing it. Interested to see your results. Good documentation!

Sent from my LG-D855 using Tapatalk


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PostPosted: Tue May 16, 2017 1:21 am 
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Joined: Sun Mar 02, 2014 6:36 pm
Posts: 351
Location: NY USA
euph wrote:
Don't know if you have done this but I have found that wrapping the electrical tape sticky side out helps when removing it....
I read that, decided to go sticky-side down. the top layer will get sanded anyway, and the tape is easier to work with.

I did take a pic of my towel wrap. This is the un-wrap after it cured. You can see, there was more ooze.

Image


Attachments:
20170512_073521.jpg
20170512_073521.jpg [ 28.61 KiB | Viewed 772 times ]

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Trek Madone 7.9 58cm 14.9lbs
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PostPosted: Tue May 16, 2017 1:23 am 
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Joined: Wed May 13, 2015 10:35 pm
Posts: 103
Fair enough. If you experiment more in the future, do try it. Hope your repair goes well.

Sent from my LG-D855 using Tapatalk


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PostPosted: Tue May 16, 2017 6:09 am 
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Joined: Wed Feb 08, 2017 2:10 am
Posts: 50
Very cool, and super interesting! But I have to ask..........why didn't you just install a longer chain to start with?


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PostPosted: Tue May 16, 2017 1:00 pm 
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Joined: Sun Mar 02, 2014 6:36 pm
Posts: 351
Location: NY USA
wheelbuilder wrote:
.......why didn't you just install a longer chain to start with?
Oversight on my part.

Last year, I set up the length for a 28 in the back, with just enough to run a 32 if needed (with care to never cross-chain). But I run the bike with a 28.

This spring, I put on a wheel with a 32, thinking "I remember that a 32 fits", without ever going over the bike thoroughly. A few rides later.... disaster. Completely my fault due to poor maintenance. In the wrap-around, it also took out the jockey wheels of the derailleur.

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Trek Madone 7.9 58cm 14.9lbs


Last edited by BikeAnon on Wed May 17, 2017 4:58 pm, edited 1 time in total.

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PostPosted: Tue May 16, 2017 4:47 pm 
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Joined: Thu Jan 08, 2015 2:03 am
Posts: 28
This is great!


Sent from my iPhone using Tapatalk


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Posted: Tue May 16, 2017 4:47 pm 


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