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 Repairing a crack in a VK2 frame
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kidneyboy
Starting Member

USA
24 Posts

Posted - 06/21/2012 :  05:55:40  Show Profile  Reply with Quote
I am considering buying a VK2 that has a small crack directly under the seat. Can something like this be repaired or reinforced. If so by whom.
Here is the description -
"and found a vertical stress crack in the frame that continues in to the seat. The crack is at the lowest point of the seat/frame and is the highest area of stress. The crack is about an 1-1/4" in length and I'm pretty sure that it wasn't there a 100 miles ago when I last cleaned it."
and a pic

I live in Wisconsin and the bike is in Illinois so I'm really looking for a solution in the midwest where I can avoid actually shipping the bike anywhere.

chuck

Speedbiker
human power expert

USA
2466 Posts

Posted - 06/21/2012 :  06:52:50  Show Profile  Reply with Quote
That is a weird looking crack, but all carbon is repairable. Grind, layout, bag. If I didn't fix it myself(I fixed much worse) , I would ask John Morciglio of Waterford Mich. He does it proffesionally.
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raymondg
recumbent guru

865 Posts

Posted - 06/21/2012 :  09:05:28  Show Profile  Reply with Quote
The resin looks thick in that area, so the crack may not be in the fibers at all, but just in the 'gelcoat' area, which would be even easier to repair. As Thom says, that should be easily repairable by anyone who knows what they're doing.
-Raymond
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LongJohn
recumbent guru

Netherlands
580 Posts

Posted - 06/21/2012 :  10:16:22  Show Profile  Visit LongJohn's Homepage  Reply with Quote
Raymond, Chuck,

Looks like a compression crack to me*.
I would perform some coin tap testing** of the area 4 inches around the crack to see if there is any delamination, this will define the total amount of damage.
Inspect the entire frame for any discrapencies, if any found: perform test test** to confirm structural integrety.
If repaired by someone, ask them their repair plan.
It should be:

1) define total amount of damage by detailed visual and coin tap testing.
2) cut out damaged material (yes, this is nevessary)
3) confim damage removal with coin tap test
4) step or taper sand the edge of the healthy material to obtain a 0.5-1.0inch repair ply overlap with the healthy material
5) clean and degrease (acetone, MEK, etc)
6) perform wet layup (or prepreg) repair with a 0.5-1.0inch overlap, restoring the same amount of plies removed, obeying the original orientation of the repair plies. apply a minimum of two additional repair plies, one 0-90 and one +/-45 degrees. Use plain weave or 5-8 harness satin carbon fibre 200gr/m^2
7) cure repair at elevated temperatures of at least (!) 50 degrees celcius

Ask if they provide you with repair warranty. If they don't, don't let them repair!

* local buckling of the material, carbon fibres are strong in tension, weak in compression.
** tap on the laminate with a big and heavy coin and hear the difference in acoustic response between healthy area's and the area directly around the damage.

Hope this helps,

Thomas (does something with aircraft repair)
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trsnrtr
recumbent enthusiast

251 Posts

Posted - 06/21/2012 :  18:59:49  Show Profile  Reply with Quote
I am the owner of the VK2 in question and can provide some more info. The crack is on the left side and basically runs vertically in the frame 13mm and then extends in to the seat area for another 10mm. There are a few lateral hairlines as shown in the above pic and does sort of look like a compression crack in that respect. The right side of the beam exhibits no cracking.

Is there that much compression at the top of the beam on a VK2? Hardly seems likely but I guess it may be possible.

Also, there is no indication of delamination as per the 'tap' test even right over the crack.

Lastly, I can't make the crack move by pushing on it or by any other motion but I can feel a slight edge.

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PoiterH
New Member

Australia
64 Posts

Posted - 06/21/2012 :  19:09:16  Show Profile  Visit PoiterH's Homepage  Reply with Quote
quote:
Originally posted by raymondg

The resin looks thick in that area.
-Raymond


It's a thick polyurethane coating.
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Speedbiker
human power expert

USA
2466 Posts

Posted - 06/21/2012 :  22:09:29  Show Profile  Reply with Quote
Who else thinks this is a manufacturing flaw and not a structural failure? It is super strong there and not likely to fail in that spot. Still affects price and needs a proper repair. A sweet bike could be perfect again.
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LongJohn
recumbent guru

Netherlands
580 Posts

Posted - 06/21/2012 :  22:38:54  Show Profile  Visit LongJohn's Homepage  Reply with Quote
Thom,

The defect in the pictures does not look like a manufacturing flaw.
Please be aware that this location "sees" the highest bending moment in the frame (tension in the lower part of the beam, compression in the upper part).

Carbon laminate can seem indistructable until you put it in comprssion. I have seen this failure mode before and is actually the only failure mode for composites that shows fatigue crack growth. In that respect this could be a crack that has been growing over time, instead of a single overload occurrence.

Thomas
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trsnrtr
recumbent enthusiast

251 Posts

Posted - 06/22/2012 :  06:19:34  Show Profile  Reply with Quote
The more that I look at the crack, I am tending to agree with Thomas. Being tucked up under there, I probably just hadn't realized there was a crack forming. My memory is vague, but I sort of remember a strange looking spot there some time ago, I just can't remember when.

Also, I ride off center like a lot of people do and I my case, that is on the left.

The big question now, is what do I do. I know nothing of CF repair and can find no one in my area with the vaguest notion of makings repairs of this kind. I don't want to ship it off for examination but would drive up to six hours to have it looked at and worked on.

Other options are to keep riding it until it becoms dangous and then part it out or sell the thing now at a discount.

For now, I'll probably ride it. In fact, I'm heading out the door for a 45 mile ride pretty quick. :)

Edited by - trsnrtr on 06/22/2012 06:20:56
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warren
human power expert

USA
4900 Posts

Posted - 06/22/2012 :  06:39:19  Show Profile  Visit warren's Homepage  Reply with Quote
Can you access that frame area on the inside?
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Speedbiker
human power expert

USA
2466 Posts

Posted - 06/22/2012 :  06:42:10  Show Profile  Reply with Quote
Have some big guy bounce on it while you look at and feel the crack. That might give you an idea what is going on. Isn't Morciglio well within your six hour range?
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trsnrtr
recumbent enthusiast

251 Posts

Posted - 06/22/2012 :  06:46:17  Show Profile  Reply with Quote
No. I cant even see inside from the other side looking through the idler hole.
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trsnrtr
recumbent enthusiast

251 Posts

Posted - 06/22/2012 :  06:47:25  Show Profile  Reply with Quote
quote:
Originally posted by Speedbiker

Have some big guy bounce on it while you look at and feel the crack. That might give you an idea what is going on. Isn't Morciglio well within your six hour range?



He's evidently swamped with other work.
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warren
human power expert

USA
4900 Posts

Posted - 06/22/2012 :  09:37:34  Show Profile  Visit warren's Homepage  Reply with Quote
Here's what I would do:

Obtain CF cloth with a weight of 10oz or so and good epoxy. Don't use the 5 or 10 minute epoxy.

* Remove seat pad. Cut a hole through the seat into the area behind the crack big enough to get your hand into.
* Save the cutout part
* Push on the crack area while watching on the inside to see if the crack goes all the way through.
* Rough up the area of the crack on the inside with some 60 grit sandpaper.
* Lay up about 3 layers of CF over the crack area. Put some cellophane wrap over the epoxy area. Jam a big chunk of foam into the hole to mash it all together.
* Is epoxy weeping out of the crack? OK, wipe the excess then slap some cellophane there too and hold it in place with foam and tape.
* after curing remove all the foam and cellophane
* Fix the hole in the seat by making some tabs or 1 layer CF to hold the cutout part in place, then use 3 layers or so over the area of the cutout with more cellophane and foam to hold it in place and mash it together.

It should be plenty strong.

-Warren.

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trsnrtr
recumbent enthusiast

251 Posts

Posted - 06/22/2012 :  10:39:22  Show Profile  Reply with Quote
Thanks, Warren. That sounds like something I might attempt.

I'm midway on a 50 mile ride and have ridden over some pretty bouncy area with my finger over the crack and can feel no flex. However, bouncing up and down while sitti g upright does seem to produce movement but it's hard to tell.
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harv
recumbent enthusiast

339 Posts

Posted - 06/22/2012 :  10:47:56  Show Profile  Reply with Quote
Dave, before I'd carve a big hole in the seat, I'd drill a hole just big enough to insert a tiny inspection light then put the bike and yourself in a dark room, wait a few minutes for your eyes to dark adapt and then turn on the inspection light. I would think if there was a through crack, you will see a light leak.

Have you contacted Garrie Hill? He is mister carbon fibre.

Edited by - harv on 06/22/2012 10:48:52
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trsnrtr
recumbent enthusiast

251 Posts

Posted - 06/23/2012 :  04:45:49  Show Profile  Reply with Quote
Harv, I could check with Garrie. I also found a place in Germantown, WI called Carbon Fiber Professionals that claim to have 20 years experience in carbon fiber repair of all kinds. Anybody heard of them? I have a sister in law in Menomonee Falls and could have it looked at whilst making a visit.
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trsnrtr
recumbent enthusiast

251 Posts

Posted - 06/25/2012 :  19:57:12  Show Profile  Reply with Quote
I'm betting that it would be an easy repair because it is so small and also because it is up under the seat where a repair really wouldn't show anyway.

Warren, After thinking about it, I don't think I could get to it from the inside.

You guys have been tremendously helpful. Thanks.
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trsnrtr
recumbent enthusiast

251 Posts

Posted - 06/27/2012 :  07:29:30  Show Profile  Reply with Quote
OK, I'm going to repair this bike myself. Any recommendations for material sources? Several sites online but thought I'd ask if people use one site over another.
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trsnrtr
recumbent enthusiast

251 Posts

Posted - 06/27/2012 :  13:12:55  Show Profile  Reply with Quote
I'm going to order away and make the repair. In fact, I'm looking forward to the experience. Thanks Alan, Warren and Thomas. You guys have taken the fear out of it.
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trsnrtr
recumbent enthusiast

251 Posts

Posted - 06/27/2012 :  18:27:42  Show Profile  Reply with Quote
I've got a practice project picked out that should work nicely to get me started. I've got an old VK seat that could use some work.
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trsnrtr
recumbent enthusiast

251 Posts

Posted - 07/17/2012 :  16:43:27  Show Profile  Reply with Quote
Well, I've got my VK2 patched. It isn't pretty, but it's done and I think it will hold up.

When I prepped the frame by removing the clear coat, I found that about a 1/3 of the crack was in the finish so the crack was pretty small. In the center of the crack was a small triangular divot which almost indicates an impact from a rock or other road debri.

A few things that I'm having trouble with is I seem to want to use way too much epoxy and have a hard time getting it squeegeed out. Of course, that causes edge unraveling from all of the over-working. Also, this crack was right in the sweet little curve of the juncture of the seat and the frame and there were changing radii everywhere. It was a bitch getting the patch to lay flat. Lastly, this was one of Kamil's mahogany finished frames and my patch is black, of course. That doesn't help esthetics any.

Anyway, I've got it patched and am currently waiting for the first coat of uv polyurethane to dry. Thanks to everyone that offered help and suggestions. I'm anticipating success even if it may be a little homely looking. Luckily it's under the edge where it's hardly seen.
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harv
recumbent enthusiast

339 Posts

Posted - 07/18/2012 :  09:21:50  Show Profile  Reply with Quote
Dennis, you can get various durometer 'squeegies' at auto paint stores. Flexible enough to follow curves and stiff enough to squeeze out excess resin. At a shop that a does a lot of glass/polyester used a tool that looked like a grooved metal paint roller to work resin into cloth and mat. The flex squeegies are useful when you sand the curves too.
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raymondg
recumbent guru

865 Posts

Posted - 07/18/2012 :  09:34:47  Show Profile  Reply with Quote
If you are good with a Dremel or sand paper, you can make the patch oversized, and then remove the ugly bits after they cure. Of course it takes a fine touch to not damage the clear coat. You can put a layer of wax paper and peel ply further out from the crack to protect the clear coat there, and give yourself an easier time.
-Raymond
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mhelander
recumbent enthusiast

Finland
352 Posts

Posted - 07/18/2012 :  14:17:50  Show Profile  Reply with Quote
I've had fairly good success in wetting cloths on top of plastic, some cloth types from both sides, then topped it with separation cloth and some absorbing fabric and rolled over from center to edges using rubber roller.

Then applied cloth to its place. Then some kitchen plastic and applied pressure using matress foam and kitchen plastic. I'm consuming quite much that nice kitchen plastic but it works well for me.

Cheers,
-Mika

MetaPhysic 700c @ 2011, M5 CrMo Lowracer @ 2010
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trsnrtr
recumbent enthusiast

251 Posts

Posted - 07/18/2012 :  14:26:24  Show Profile  Reply with Quote
I used plastic and thought that I had most of the epoxy out but there was obviously more when I applied the patch. The different radii reminded me of a calculus problem the way the curves were changing in all directions. It was really hard to get the patch today flat.

Anyway, the patch is on and it sanded out pretty smooth. If it wasn't for the different color and the ragged edges, I'd be thrilled but I'm pretty sure that structurally, I succeeded even if it is a little homely looking. :)
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