Hello,

A little background information. So I was picking a Campagnolo disc wheel when seller started swinging a Vicini TT bike with almost complete C-Record group asking if I was interested. Sure I was so I bought that one, too. Bottom bracket, crankset and seatpost was missing.
I also got Carnac shoes that are barely, if at all, used. These are with some kind of Time cleats that are new to me. Seller had Time pedals on a bonded carbon frame somewhere in a corner. As he has no use for any of these, in a few days I asked if he is willing to sell these pedals. He offered the whole bike that had some nice bits (Shimano tricolor and Dura ace), also I noticed C-record crankset and bottom bracket that are originally from Vicini TT, so I went to buy this bike too. Price was reasonable.

Seller said he bought this bike in Belgium in early 90's and raced some races, including cobblestone ones, also training rides. He said the frame was very flexy, but not crashed.
At first I planned to put the C-record parts back to Vicini and maybe build this bonded frame for occasional relaxed rides, but after inspecting it looks like it is suitable for a wall art only. Vicini story is here:
Vicini TT bike: strange bulge on DT?

So, this is an Advanced Composite Technology Winning bike, a rebranded Alan Carbonio, no Alan markings. Theres a "K" and "DAMS" sticker on seat tube, maybe some kind of Belgium bike store?
Anyway, I noticed that bb shell is cracked at the drive side, the crack is full thickness, can be seen from the inside of bb. Went for a 5 mile spin and bike rides very nicely, but flexes laterally quite easily.
I have seen (here and alsewhere on internet) some of these frames fail at bonding sites and maybe at seat tube-bb connection, but can't remember seeing this type of failure. Is it some kind of manufacturing defect or a fatique crack?

Nice wall art now I think.

how it happened is speculation, it does not really matter, the way the tubes converge, to take it apart will most likely damage one or more tubes, then you need an exact replacement shell.
Welding up? I don't think so.

Probably Kurt Dams in Veerle, near Tessenderlo.
I've seen twice a crack in the bb-lug before. Lateral flex is normal for Alan, certainly with strong riders and bigger frames. It depends how much flex ...
I know a lot of people ridin' with a crack in a lug, most of the time the head-lug. My lady rides that way for years, on a lady-frame, no uppertube! I myself got one with a crack in the seat-lug. It has never been a problem.
Aberto Falconi, the AL from Alan, seems to have said there are no riscs ridin' with a crack. The glue is more important, so never weld a crack!

In the Alan-group on FB this passed by, one of the responses, maybe it helps.

Thanks for information and thoughts!
I'm not intending to repair it, maybe it could be done, as Fabiofarelli found in FB. Nearby there are no experienced CV bike welders that I am aware of, and, in any case, I am (overly)cautious about these things.
I'm more curious about the causes even it will not be repaired, I like to find out about these things. Could lateral flex induce these, like a fatique crack from lateral motion?

I'm quite surprised it could be not that dangerous. When I took it for a spin I was thinking it could disintegrate any moment I will think a little bit more and maybe it will be my easy cruising bike someday.

I cannot help you with the reason. As always, probably it's a combination of factors. In my idea small frames usually have no cracks ...
And the other thing, maybe you should be able to compare with a ride on one with no cracks. Too much flex seems risky to me. But what's too much when you never rode another?
I'm small and I only ride quiet, no racing and I have no problem with the flex. But also I have no crack in the bb.


Picture just for fun, not mine.

That's a strange place for a stress caused crack...

What I suspect is the aluminum casting that the BB shell was machined from had a manufacturing defect that was visually undetectable at the time. There are a number of causes for these kinds of "seams" but that's more than I want to get into.

My suggestion would to be get a strip of carbon fiber fabric long enough to wrap around the outside of the BB shell and overlap at least once.

Thoroughly clean the area to remove any grease or dirt then rough up the aluminum surface with some coarse sandpaper.

Next apply some high quality structural epoxy to the area. Wrap the carbon fiber over the epoxy making sure that it's being absorbed by the fibers. As the epoxy starts to harden apply a second coating over the fabric.

You could also apply some epoxy inside the BB but chasing the threads to remove the excess would probably damage the aluminum threads. A threadless BB like the old Mavic cartridges would eliminate chasing the threads.

Some of the early Klein frames had boron carbide fibers epoxied to the BB area.

Sorry for your misfortune....



verktyg

[QUOTE][/That's a strange place for a stress caused crack...QUOTE]

And one of the most common places. I think the under head-lug is most common and this one is pretty close. But seldom a problem, surely if you keep your hands off the headset.

site
Without the use of an oven autoclave and or a vacuum in a heated moulded press the trapped air will render a backyard resin/carbon matrix exactly as strong as fiberglass ie not very strong. The reason CF is so much more expensive than other material is the very expensive ancillary equipment necessary to make it monocoque. The materials themselves are just cheap plastics.

Maybe you could "Fred Flintstone" a repair, using a hose clamp around the shell?

The aerospace industry uses adhesives that bond aluminium together. The bond is far superior to welding or riveting but once again requires very toxic preparation and is oven cured. They even have a n Al adhesive emergency patching kit for aircraft stuck on the apron but a kit would cost as much as the bike brand new.

There are two four ways I might go about this. All could be used in parallel.
1) Drill a small hole at the end of the crack so that it doesn't propagate farther.
2) Screw in a good quality BB cup with some strong epoxy like J-B Weld or Loctite Epoxy Weld or Araldite 2011 all over the threads, and just never take it out again. This would shore up the area rather well, I think. If the bike ever fully broke, you could heat it up and liberate the cup without damaging it.
3) Fabricate a "corset" to hold the BB shell together. I'd make a split ring out of steel or aluminum and have it bolt together like a seat post clamp.
4) Just ride it, but monitor it regularly. The trouble getting worse should first manifest by the cup unscrewing (if Italian, right-hand threaded) or shifting/clunking (feeling like a loose BB bearing), I'd think. I bet it will be pretty obvious before anything catastrophic is at risk to occur.

The weld repair was done to an aluminum tubed bike.
no mention of the actual process.
only hint was that the threads required chasing, that indicates to me that the weld had full penetration, I suspect a V groove cut to get a clean weld face, and maybe a stop crack drill.
be good to see how extended the crack was before the repair.

I still vote wall art

"I still vote wall art"
I have to agree. I have always assumed the biggest stress on a bike was borne by the BB. Whether standing on the pegs and crunching over a pothole or giving the full gas going up a hill. The BB shell is normally 4 or 5 times thicker in steel and is a very tight radius for superior rigidity. A crack there spells doom for my two cents worth.

Sorry for a late response. As always, thank you all for responses!
I don't really need a n+1 bike as I have more or less intact steel ones, so this frame will be wall art, at least for now.