So my buddy snagged a warranty replacement bike last year. It has a slight crack on the seat stay, and was likely destined to be junked. The only damage is this rear stay, and the rest of the frame appears to be solid.

I was under the impression it was a 56cm when I got it, but unfortunately I found its a 58 after measuring. Thankfully it was a good deal, and this will be good practice working with composites. I found a matching fork for $50, and the going rate for this frame used with a fork, is in the neighborhood of $800 (for a not-broken one). All said and done, I will have just a bit over $100 into the frame and fork (missing one dropout, no headset or BB) once repaired. It will be a few grams heavier than the original, but I like to think it will be worth more than what I paid

Not sure what I am going to do with the frame after repair, probably send it to my uncle who is a big time roadie. Unless someone here wants to trade me something in the 54cm zone, or roadie components...

I am doing all of this work with a friend who has worked in composites for years, primarily in aerospace. This is his first time working on a bike, but it should be interesting to see what happens.

Here it is...



So I located the crack, and sanded the paint off with 150 grit. Its amazing how little paint is on these frames. I gave about two inches on either side of the crack, and went all the way around the tubing. (The crack probably runs 1/3rd of circumference) Had to be pretty anal about not sanding too hard, so I didnt compromise the existing carbon. Checked for more cracking visually and didn't see anything. Could go to campus and set up some sort of ultrasonic testing rig, but that seems like too much work. On summer break.



Finished sanding.



Next step is to do a few wraps of carbon around the sanded region, then some finishing work.

more to follow...

Very interested to see how this precedes. There's a couple guys here in the UK making a living out of doing just this.

How d you intend to repair the drop out and replace the hanger?

+1. Repairing the chainstay crack seems pretty straightforward but the dropout is going to be a lot trickier.

https://item.mobileweb.ebay.com/viewi...id=02176054218

The hanger looks to be the replacable type, so should just be a bolt in replacement. You can see the screw holes in the last photo, and these appear to match this https://www.cannondaleexperts.com/Can...158_p_271.html

exactly. Every removeable part was taken off the frame before warranty. Luckily I can get a drop for $25.

It's a derailleur hanger, more precisely.

IMO that repair will probably work well, given the seatstays mostly just see compression. I'd soak the crack in resin before applying plies; prolly some longitudinal to start (IMO you only need it over the crack), then a tight spiral over the top.