Yeah, unless it's a top level race frame and you're a top level cyclists, it's not worth it.

In addition, you see the outer repairs but I rarely see anyone inspecting and repairing the inside.

Mine was a Madone SLR 8. Did not have the kind of budget to replace it Paying the first time was bad enough. And I am pretty much the top level cyclist in my house. Top 2 anyway.

Yeah I agree repairs tend to be layered over the outside. Question is whether that’s enough to counter the risk. I mean there are bound to be damage situations where that is not going to add enough strength.

It doesn't sound like it would be a worthwhile project for the OP, but this is the kind and location of an impact that I would be very tempted to fix myself. Sand, three tapered layers of CF cloth and resin, electrical tape with pin punctures and then final sanding. Paint or not. It won't look any worse than it currently does, but it won't fail.

Carbon repairs should not be done only to the outside. Any internal damage will continue to propagate until it is far beyond the repair area until eventual failure. A proper repair involves mapping out the internal damage by some means, (X-rays, sound, etc ..) removing all of it, how ever deep down and wide it goes by means of abrasion. Then examining the layup and orientation of each layer and making a pattern with successive layers of mylar and sketches of each. Then Re-laying down each piece in the proper orientation in order with an all encompassing additional top layer. From there a vacuum bag and heat. When cured, sand and blend the top layer to the unaffected areas, primer and paint as normal.

The difficult part of a bike tube is backing up the back side of the repair should the damage extend that far down. Surely there must be a way with an air bladder or expanded and profiled foam or whatever, but that's what the professionals are paid for.

So yes. The inside must necessarily be examined. It's just accomplished from the outside.

Considering that the primary stresses are to the outer skin of a tube, I'm not sure I agree that an outer repair will fail to arrest any cracking.

In general, yes, however with a *thin wall* tube, the limiting factor can sometimes be (resistance to) localized buckling, when that local portion is under compression. In slender columns, the resistance to buckling is a function of the material (elastic modulus) and geometric (section modulus) *stiffness*, not strength. Similarly, in thin wall tubes under bending and torsion, the resistance to localized buckling can be a skin stiffness issue.

If you do a search for <B-52 fuselage wrinkling>, you will see plenty of photographs showing much local buckling in the forward section in front of the wings, the direction of buckling for "longering" (square skin element trying to turn parallelogram), under high positive wing loads (wing pulled hard up, thus fuselage pulled down by gravity and inertia), limited by the semi-monocoque ribs and stringers; The stresses are taken by both the skin and reinforcements that prevent localized collapse of the skin.

The lower the elastic modulus of the material, the more susceptible to localized buckling. This can be mitigated with ribs and stringers, but also, a "sandwich" material, with thin outer and inner skins separated by structural foam, or a "honeycomb" core of the same material as the skins; Fiberglass skin with foam core is common on small and large sailboats. Honeycomb aluminum and composite panels are common on aircraft. The XB-70 (Mach 3 cruise) required stainless steel honeycomb panels with the skins brazed to the cores, to stand up to the heat at max cruise. ($$$$$$)

Depending on the OP's risk tolerance, he might simply leave it alone and ride. This is what I'd likely do if it were mine. Take a close photo up showing the paint's crack pattern, or mark a few small dots along (not over) all existing cracks, to document the status quo. Then periodically recheck for changes.

There are also various stress indicating coatings that either change color or show obvious cracks at specific stress thresholds. The drawback is that one has to know the stress level target.

Understand that the decision also depends on the circumstances. For example, while I wouldn't buy it, I might build it up if I already had components, and would more likely keep riding it if it were already a favorite ride.

So, engineering and structural considerations aside, it boils down to a judgement call.

I’ll bookmark this and let you know how it goes in 10 years cos I don’t intend to retire this frame during my lifetime

Seriously though I trust these guys as do hundreds of riders around here in London’s main cyclist homeland. Maybe they do that if needed, no idea what they did on mine. Never heard of a repair of theirs failing.

Personally I wouldn’t sell the OP’s frame without a professional repair but it’s probably uneconomical

Handlebar impact?
I've seen this type of crack when a rider crashed at very slow speeds, with the handlebar hitting the frame, and the rider's weight on the bars increasing the impact.
(They rode it back to the car, carefully, at slow speeds.)

Professional carbon repair
That looks very repairable. It's pretty easy to wrap a section of a tube like that back to full strength. Search results.
(I think that wrapping is effective even without an internal bladder -- it's not nearly as lightweight as the original frame, but all that extra carbon layering compensates for the compression of the original bike manufacture.)

For exmple, Calfee does guaranteed repairs, along with their original carbon frame business.
Ruckus Composites does repairs, and even CNC machines new carbon dropouts if they are broken.

Calfee examples:
https://calfeedesign.com/carbon-repair/

That old frame might not be worth repairing by these services, though.

Ray Magliozzi, one of the Car Talk guys: "Uhh... you're done for."

The soft spot may behave better than a crack in metal, where that crack end is a big stress concentrator, and will continue to grow (which is why, drilling a small round hole to end a crack, often works). You have a good amount of redundant load paths in the carbon around the crack, the question is how much localized (in material plane) compression or shear loads you get at the soft spot. If it was just a townie riding slow, I might ride and monitor, but for anything off-road, or fast rides, or long tour, I wouldn't take the chance.

By the way, a respected LBS recommends against carbon ANYTHING, unless you are in competitive racing, due to fragility, bad failure modes, and also hazards of sharp edges on such:

https://rideyourbike.com/carbonfiber.shtml

They’re right. Hundreds of deaths a year from carbon bikes. The industry is worse than tobacco.

Geez, that many?! I'd sure like to know how, whether it was structural failure of the frame, or when failing, the sharp edges cause more damage than hitting the ground?

No

I should have cracked out the saracasm emoji, sorry.

I think he's being facetious, being a carbon owner himself.

Don't see many options, since I can't ride this bike myself, I can't get away with ugly CF patch to flip it. It's either selling bike as is for peanuts or strip parts.

I thought you originally bought it for parts.

If so, not getting the surprise bonus that might have been, simply restores the original status quo.

Therefore nothing to regret.

I don't get a rush from gambling, so getting a steal on a bike is the next best thing 😂.

And you got to enjoy that rush for a while. So you actually came out ahead.

Ah OK. That is pretty good sarcasm, now that I get it. I might borrow that for talking about e-bike battery fires. I wonder if there is a corollary of Godwin's Law regarding tobacco?

https://en.m.wikipedia.org/wiki/Godwin's_law

Way ahead, just doubled the money on the frameset, and still have all the parts. Interestingly, the buyer purchased it to replace his Roubaix that developed a crack in chainstay. He didn't remember crashing or hitting potholes, which is concerning since I have a similar model year Roubaix.

That must have been a hell of a chainstay crack for this to be a better option

Can't ride with a chainstay crack, where is this can be ridden for a while, especially with a patch.

Oh, much smaller diameter tube for a chainstay, makes any given damage, much more severe. Top tube is lower stress, larger diameter. For top tube, in bending, tension, compression, lots of redundant load path around that soft spot I think. More critical I think is when standing on the pedals and pulling hard on the handlebars, both down and top tubes in torsion, whether there will be any localized buckling at the soft spot, or expansion of it due to fully-reversing shear stress at 45 degrees to the long axis.

In addition, carbon expert Rob explained in one of his other videos that manufacturers reinforce the bottom of top tube, since this is the most important part. They specifically mold the top of top tube thin for "weight savings".