I crashed my Cannondale Caad 7 several years ago, putting a dent into the top tube (from the handlebar). I rode it for a short while after that, but a small hairline crack developed in the dent and I havn’t touched it since. The frame is in great shape otherwise. I have to move, so I’m getting rid of all my extra stuff…so I’m wondering if there is any way to repair such a dent/crack. If not, it’s gotta go. I’m a student in the UCLA Engineering dept. and they have an awesome machine shop with guys who can do some amazing things. So if lack of expertise/tools is not an issue, is there any way to make the frame safe again? Anyone have experience with such things?
The only way is to replace the entire tube. That may or may not be possible with a welded aluminium frame, but it is unlikely. Generally speaking, aluminium frames are not repairable.
i’ve never cracked a road bike frame, but some mountain bikes and there’s never been any attempt to repair them. but mountain bike frames (at least the quality stuff) come with a lifetime warranty - i guess road bike frames don’t…
I had a hairline crack in the soldering joint of the top tube with the headset and I had to ditch it… this is also why I’ll never buy a 2nd hand bike that has been repainted.
It would be chaepaer to buy a new frame than repair the one you have. I broke my MTB frame from C’dale years ago. They sent me anew one right away for free. Call them up and ask.
Sorry, your bike is toast. Once the crack gets big enough to be visible then one good pot hole and you will be riding a unicycle. I would make it completely unrideable after stripping it so some poor dumpster diving soul doesn’t kill himself on it. If you are in engineeering, give it to the mechanical engineering students and let them cut it up and do some fatigue testing on it.
It might be possible to repair the top tube fairly cheaply, but it’s not going to look pretty. I used to design repairs for damaged fighter aircraft. The majority of structural repairs on cracks were nothing more than drilling a small hole at the ends of the crack, polishing the holes (to keep the crack from propogating), bonding an aluminum patch over the damaged area, and reinforcing the patch with blind fasteners (rivets). If the crack is small, bonding a large enough patch over the crack with a very strong adhesive may be enough. Basically you want to create a new stress path around the damaged area. I presume your machine shop can form then heat treat the aluminum patch, or machine one from treated metal. It’s important to do good stress analysis. Since you have access to the engineering department, you should be able to find someone to do the analysis. Back-of-the-envelope analysis should be sufficient. A lot will depend on the strength of the adhesive you have access to.
I second the small hole drilled at the end of the crack. You have to guesstimate the crack lines end ,which can be 1/4" ahead of the visible crack . A straight crack is simple ,when they snake like a river determining the end is more guess work than science.
Being that the bending is of a low cycle / freq. ,I doubt it will just let go one day and break while riding .