Repairing Aluminum with Carbon Fiber

Last year my Ksyrium Elite rear wheel developed a crack in the rim near a spoke. I rode it for awhile with this crack thinking I had a loose spoke. Once per revolution of the wheel a clacking noise was heard and a tiny thump could be felt through the bike, if I’d kept riding it it would have eventually ripped through. I haven’t had any luck finding a replacement rim nor have I bothered contacting Mavic for a repair. It’d be a waste of my time. I decided to try something that’s been on my mind for a long time. Fixing aluminum with carbon fiber.

Now if you’re thinking, geeze Matt, what are you doing, you don’t have a clue how to work with composites, then you’d be right. I have no idea, I just spent 15 minutes looking up this stuff on google, but don’t fear for my safety. Twice spokes have broken on this wheel and neither time a crash occurred. The absolute worst that could happen is the spoke yank through the rim.

I know carbon fiber can be bonded to aluminum, I ride a bike made of carbon and aluminum, plus all kinds of alumimum parts are bonded to a full carbon frame, sure with some ultra powerful epoxy that cures at 350 degrees, but we’re just talking about fixing a crack, so I gave it a shot. I started by ordering some West System 860 Aluminum Etch kit. This stuff stops aluminum from forming an oxide which prevents stuff from sticking to it. Should be useful for other projects should make paint stick to aluminum.

Next I bought a carbon kit from ebay that had about a yard of carbon and enough epoxy to wet it down. Kind of reminds me of snake skin.

I found the the crack and drilled a hole at the end of it. This is suppose to help stop the crack from continuing, shear forces or some such.

The next step was to sand it and apply the aluminum etch. The label on this stuff is scary, causes birth defects, cancer, death, I went ahead and wore gloves.

Next step was preparing my carbon fiber layup. Apparently it takes about 7 layers of carbon to create the thin parts of a frame and up to like 20 for the thick parts. I went with 3 layers, or piles as they seemed to be called. The carbon wasn’t to hard to cut as long the pieces remained large, smaller pieces wanted to come unraveled a bit.

The next step was mixing up some epoxy and wetting down the carbon. You’re supposed to brush on the epoxy then use a squeege or something to press out excess epoxy. I forgot that step, opps.

The step was slapping the carbon on the rim. I had used a leather hole punch to make holes but found it nearly impossible to getthe holes go where I wanted, I eventually just kind of gave up on that.

The next step was wrapping the area in electrical tape, sticky side out. I was supposed to put tiny holes in the tape so that excess epoxy could seep out, I didn’t bother with that. The tape did squeeze out some epoxy.

Let it cure overnight in a warm dry place.

A few minutes of sanding and I’ve got this. Not exactly pretty, but if it holds up great. I won’t be able to adjust tension on this spoke more then likely, but if I could get another year out of this wheel then it will have been worth it.