DIY fixing damaged carbon seat stay
 

The patient: 56cm size carbon frame Corratec road bike.

The wound: a cracked seat stay, with multiple small fissures over about 12cm length - I guess the bike has fallen and hit a kerbstone or similar.


I've been quoted about 400-500 pounds to have it repaired in the Philipines.


I cant see why I cannot make a DIY repair, using 2-pack epoxy.


My plan: Drill a small hole above the limit of the damaged area and pump in liquid 2-pack epoxy to completely fill the inside of the seat stay - to make it a solid casting.


Over to the critics: is this feasible, practical, desirable? Or should I pay money to leave it to a professional?

Lots of YouTube videos about doing the repair yourself with carbon fiber kits/materials. Do a search for Carbon Fiber suppliers that ship to the Philippines and do some research on the best types to use for your bike and various sellers offer "CF bike repair kits" but I suspect you pay extra for the supplies in kit form. Some CF sellers even have articles explaining the best types of cloth and resins to use. Be prepared to spend a fair amount of time researching what CF materials and methods to use.

I've no idea what your damage looks like. However typically I wouldn't just pump epoxy resin into it and call it ready for prime time. Properly you should sand and feather back from the damaged area and then lay in new cloth and resin. That will better address the tensile, compression and torsion forces that area of the stay is supposed to bear.

If you just fill the entire thing with resin, then it's possible it might fail faster. Or at least make the bumps you hit while riding, bumpier.

Some carbon frames have had a release agent applied to the insides of the frame, to better allow the compression bladder to be removed after inflation and curing.

Epoxy makes for a poor structural material, great as a bonding agent but bad at other things.

Just about every carbon frame repair I have seen uses tow wrapped around the damaged area.

Do the repair estimates include refinishing? Even spot paint touch up can add a bunch of cost. Andy

thx Cranky, but that's not really where I'm aiming for. I've looked at the YT videos and looked at fibre kits. I dont really want an external repair. Hence my idea to fill internally. Looking at next reply #3 it seems it's ore complex an issue than I thought.

Exactly the sort of reply I dont want! I didnt think of that!! Useful, thx.

Carbon fiber (crabon febray?) is super repairable. I have a hard time believing that the nearest possibility is The Phillipenes.

Generally the brocedure is to sand out all the damage. Make a replacement layer of the right shape & orientation for each layer sanded out. Add 1 layer over top to encapsulate the repair. Vacuum bag it & apply the right amount of heat.

I took a 2 day class with a former employer. It's not particularly hard. It's getting the materials & tools that stops the "Everyman."

When I had my Cervelo chainstay repaired, it was $500 for a basic functional repair, $800 for undetectable perfection. The factory correct paint, prep, & load of TLC costs $300, apparently. On the plus side, return shipping was free!

Look local. Ask a variety of shop mechanics if they "know a guy" or who they would recommend. Some of the best carbon fiber bike productss made in the world come out of European origin.

More technical details I hadnt thought about. Unwelcome reality - but thx again!

I would not ride a bike that was just glued back together with a ton of glue. If you don't want to do it right, don't do it. Either get it to the professionals or say hey I will get another bike. There is a reason good carbon bikes costs that money and good carbon repair does as well. It is not just a gluing a model plane back together to put on display (unless you are putting the bike together for that purpose then go for it).

If this were a frame I loved I would spend the money to get it repaired properly if I didn't care about it I would just get a new frame. I am not an engineer and I don't really do frame repair and my time is generally more valuable (though these days I have a bit of extra time) I don't personally want to work with carbon fiber and the dust in my home I would rather have a professional do it in a space that is hopefully better set up or at least it is not my space and my lungs dealing with it.

That would be fine if epoxy had the right tensile properties, but it doesn't which is why it's only used to glue the structural fibres together. My plan would be to remove the damaged section by sanding it until there are no cracks remaining; this should leave the stay in two pieces with a gap in the middle and feathered edges. Then epoxy a pre-made carbon tube inside (you'll first need to scrub inside the tube ends with a gun brush and acetone to remove any release agent) and layer carbon over the outside to restore the original dimensions.

All understood, including the point about lack of tensile strength. Your post rather points me towards relying on a professional workshop. I simply dont have the facilities (or probably the skill either).

If you don't care how it looks, but just want it fixed, you can try this:

https://www.amazon.com/Carbon-Repair.../dp/B00UMATXWY

Seat stays are not really load bearing and there are plenty of people who fixed their MTB seat stays and huck the crap out of them.

I don't know about retail availability, but there are structural urethane (and other) foams made for applications like this. I wouldn't trust them for a downtube, but given that both the loads and potential consequences are low, that might be the kind of solution you're looking for.

Otherwise, I'd lean to some kind of exterior wrap reinforcement, then do the same on the opposite side for cosmetics.

"I have a hard time believing that the nearest possibility is The Phillipenes."

..... unless the person posting that location is also IN THE PHILIPPINES or nearby.. :-D

Seat stays are under a high COMPRESSION LOAD when the bike is being ridden.

Other loading that occurs in a bike frame, when ridden, are Tension, Shear, Torsional, and Cantilever loading.

update: A squealing Brake can cause Extreme VIBRATIONAL loading of the seat stays... :-D ,,, might just Shake that Epoxy into Dust.

the compression loading of the seat stays reduces the cantilever loading of the bottom bracket/chain stay interface. the comp.load changes every time you pedal.... Load Cycling Fatigue (Loosening of the Epoxy's bond to the fibers) set in and the seat stay failed by turning itself into useless fluff and chips.I've seen one frame like you describe... it went into a dumpster after a close exam and being cut to prevent reuse... that obvious failed seat stay was only the outwardly visible failure... the head tube was trying to fail also. A broken seat stay will ruin your ride.. A broken head tube joint may end your life.

in the OP's case, I'd be looking for additional cracking at the BB/Chain stays junction...

my advice to him/her? BUY A NEW FRAME.

Seat stays are load bearing. They bear compression. They bear the entire weight supported by the rear wheel, which is 60% of the total weight.

All parts of the frame bear load. If there was any part of the frame that wasn't necessary, it would have been eliminated to save weight.

If your car seatbelt was cut, would you just stitch it back together with your grandma's sewing kit and call it a day? No.

Your frame is busted. If you can't find a professional to repair it, it's time to throw it in the trash.

Anytime I consider a makeshift repair I consider 2 things; likelihood and consequences of a failure. In fact those are critical issues engineers deal with all the time. For example it's why aircraft have redundant systems and cars don't.

In this situation let's deal with potential consequences first. Of all the places to have a sudden catastrophic failure, seat stays would be among the least likely to lead to a serious injury. So, I'd be far more willing to try my luck there than, say, the downtube.

As to likelihood, that depends on how damaged they are now. If the damage is more like bruising like from a side impact, odds are that they just need a splint to prevent buckling. Therefore filling with structural foam may be very workable.

The OP also factor his options. Here in the USA there's easy access to qualified help, so it's only a question of cost. However, that may not be true in the Philipines.

Watch this:


Talk with someone like Rob English.

Seat stays are in place because the UCI dictates what makes a bike frame.

Fixing carbon is easy. Roadies are failing to learn things that mountain bikers learned years ago.

Road bikes design is dictated by the UCI and racing rules - which is the reason why the whole "aero" bike thing is a joke. Lipstick on a pig.

I haven't laughed this hard in months.

You do you buddy LMAO! Knock one of your seatstays out with a hammer, then do a descent. Report back afterwards and share your results. I have no doubt certain dirtbag 13 year old mountain bikers have fixed their frames with Gorilla Glue and cling wrap. The difference is that I'm a real adult with a real job. This is pocket change hobby money. My life is worth more than trash. Are we bums here?

By the way I get email alerts to message replies, so I'm able to see what you wrote originally before you edited your post, which is even more hilarious.

Quoting you: LOL! Yes, seatstays exist because UCI dictates it. It has nothing to do with the fact that the seatstays are the compression member in a triangular truss without which the truss wouldn't exist. You're absolutely right lmao... :lol::roflmao2::roflmao:

Sorry but what? Seat stays are there because of the UCI? I am baffled by that one.

Triangles are generally regarded as one of the strongest shapes, that is a big reason for seat stays to make a stronger more rigid bike. A bike without seat stays could probably be done but I don't see a benefit at all and I don't know without some crazy chain stays it would be very stable and reliable.

Looking through Rob's site which is always a pleasure because he is such an excellent bicycle builder there is only one adult bike that essentially used a massive downtube and went all the way back everything else had seat stays (there was a balance bike and a bike for a very very short person or child that didn't but much different needs) He did make project right but that had a seat stay. I would think as a custom builder who can build a right handed bike and so other really amazing things would have gotten rid of seat stays it they were not important. He is a private builder and doesn't have to submit that frame to the UCI if he doesn't want. I would think if I were a custom builder and had found the secret to bicycles and it was no seat stays I would build a lot of bikes like that. Unless there is a held belief that the UCI is some sort of Mafia like organization and has put the screws to English (You better put the seat stays on or we will let you swim with the fishes).

The OP used the term "kerbstone." This lead me to believe that not only was the OP in a location that not only had that spelling, but also in a location that kerbstone was also part of the vernacular.

North America would use the term "curb."
Australia and nearby New Zealand would use "kerb."
We have very few posters from Russia, Africa, South America, or Antarctica here on the forum. So, the OP originating from those regions of the world is unlikely.
There remains the rare possibility that English language influenced India or South Africa may be a possible location but also equally unlikely.
Asian origin doesn't fit the "kerbstone" and the speech syntax of the post is that of a native English speaker. Switching language systems is hard. For a variety of reasons, including personal vulnerability, a question, especially one concerning great personal cost, would most likely be asked on a forum that caters to the OP's native language.

This leaves the possibility the OP must be of well Englished European origin & comfortable enough to ask a question in their non-native language. From all that, I deduced the OP is most likely from within one of the 4 countries that comprise Great Britain. Specifically, I guessed England for no particular reason.
I therefore tailored my answer to that end.

Between Darimo, Carbon-Ti, Ax-Lightness (and their parent company Beno,) THM and several others, odds are there is a lot of expertise in the European Union. Bike components is but one facet of the entire carbon fiber manufacturing industry for which there is often knowledge spillover as workers cycle in & out of various employers. Both of these factors combined with the considerable amount of trade & migration between the EU & the posters deduced country of origin work support my conclusion:

The OP has a good chance of finding the expertise he needs within a 1000 mile radius. No need to ship the bike frame to the other side of the planet. Further, the nations of Great Britain have embraced cycling whole-heartedly. I'll wager repair services are available within 100k radius. It could probably be hand delivered to the repair facility if he/she/they asked around a bit.

For the particularly observant, you'll no doubt take note that I didn't touch various socio-economic wealth factors that would determine the likelihood of even owning a carbon frame bicycle in the first place much less having it repaired. It simply wasn't necessary for this exercise. It's a safe bet the OP is in the upper portion of the global wealth distribution; Ruling out The Philippines. (<------ maddog34 Good catch on the spelling, BTW. :lol: )

Op: How'd I do?

Some excellent analysis and deduction in evidence, Sir. However you do fall short in one aspect because you fail to take into consideration that I might be Anglophone but expatriated. This is indeed the situation. I live/work in the ME, where service industries are king! but the local market still is not able to effect repair; their preferred course of action is to ship to Philippines for repair. To be fair, Philippines isnt so far from here; certainly not half-way round the world.

Back to topic: this thread is of value to me because it has exposed the immaturity of my idea, the assumptions without basis etc. Having read (and on occasion giggled at) the comments, quotes and responses; I'm pretty much of the opinion that:

1. Carbon repairs are entirely feasible, and may not even be demanding (as a discipline).
2. Sanding carbon dust into my lungs is not going to end well. Specialist eqpt (including PPE) is likely required.
3. Epoxy fill is not the answer, by itself.
4. There are people who will condemn me for attempting repair. The frame should be binned.
5. I deliberately didnt post photos of the damage, in order to gather a wide range of opinions.
and finally
6. The frame is off to a workshop in the Philippines for repair.

Thanks to all comers for their input - mainly good-natured!

Rats... I've been TROLLED!!!

https://cimg6.ibsrv.net/gimg/bikefor...e14556eb0.jpeg

I've made some webbing straps using grandma's sewing machine with ordinary polyester thread and they're totally OK for the intended use (hitching a heavy load to a winch and winding it up a steep ramp). There's really nothing special about it, get the tension right and put enough stitches in to spread the stress. I keep meaning to restitch them with some heavier bonded thread, but they show no sign of failing (and if they did it would mainly just be inconvenient). The proper thread to use for seat belts is UV-protected bonded polyester, which stretches less than the equivalent nylon and I'd buy some of that if I was making up a safety harness. Old hand crank machines arguably do a better job than industrial machines as the low speed means the thread doesn't get heat stressed.