MCFK Stem hairlines Cracks

Discuss light weight issues concerning road bikes & parts.

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elfuinha
Posts: 978
Joined: Sun Aug 08, 2010 10:18 pm

by elfuinha

Hello

After my ride yesterday, as cleaning my bike and notice this crack on my Stem, Upper Clamp of the Handlebar.

The cracks aren't seen in normal light, and you can fill them passing the fingernail.

Anyone add this problem.???

Before anyone start saying that is overtorque, it isn't and it wasn't, this stem was torque to Spec, with carbon paste, Effecto Mariposa 1-8Nm so fine tunning, and torqued to 3Nm acording to the manual of the Stem.

let me know on this.
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corky
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Location: The Surrey Hills

by corky

I'd speak with MCFK rather than a bunch of know alls on a forum.......but that's just me.

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Lucendi
Posts: 606
Joined: Fri Jul 19, 2019 10:37 pm
Location: Sweden

by Lucendi

The lines you see are the different layers of carbon fiber that have separated/become delaminated.

I have two MCFK stems, one looks similar to yours and one doesn't. The one with the delamination I got brand new and came like that from the factory.

I wouldn't worry about it.

elfuinha
Posts: 978
Joined: Sun Aug 08, 2010 10:18 pm

by elfuinha

Lucendi wrote:
Mon Dec 13, 2021 5:26 pm
The lines you see are the different layers of carbon fiber that have separated/become delaminated.

I have two MCFK stems, one looks similar to yours and one doesn't. The one with the delamination I got brand new and came like that from the factory.

I wouldn't worry about it.
Hello Thanks fot your answer.

I've 3 of them and this is the only one that is like this, but just the top part, the bottom isn't, i've asked MARTIN from MCFK, waiting for an answer from them.

elfuinha
Posts: 978
Joined: Sun Aug 08, 2010 10:18 pm

by elfuinha

elfuinha wrote:
Mon Dec 13, 2021 5:18 pm
Hello

After my ride yesterday, as cleaning my bike and notice this crack on my Stem, Upper Clamp of the Handlebar.

The cracks aren't seen in normal light, and you can feel them passing the fingernail.

Anyone add this problem.???

Before anyone start saying that is overtorque, it isn't and it wasn't, this stem was torque to Spec, with carbon paste, Effecto Mariposa 1-8Nm so fine tunning, and torqued to 3Nm acording to the manual of the Stem.

let me know on this.

tjvirden
Posts: 540
Joined: Sun Nov 22, 2020 9:21 pm

by tjvirden

With what Lucendi has said (receiving a new one, like that) then from your pictures they're most likely planar voids from manufacture.

Assuming the MCFK stems are made from prepreg carbon, then it's not hugely surprising - when laminating many layers of prepreg, it's difficult to be sure that no air is trapped between the layers. Any air that is trapped is really difficult to remove with so many layers - even when using vacuum + autoclave.

I don't think there's any chance at all that your stem will fail from these, but lets see what MCFK say.

Reliable void-free manufacture is one reason THM moved to resin transfer moulding for at least some parts.

elfuinha
Posts: 978
Joined: Sun Aug 08, 2010 10:18 pm

by elfuinha

Just recieved an answer from MCFK, they want to see the stem, and are asking to return it.

And they assume the Stem was overtorqued, but it wasn't, let's see.

Waiting for a 2nd answer, to know what to do.

elfuinha
Posts: 978
Joined: Sun Aug 08, 2010 10:18 pm

by elfuinha

tjvirden wrote:
Mon Dec 13, 2021 6:43 pm
With what Lucendi has said (receiving a new one, like that) then from your pictures they're most likely planar voids from manufacture.

Assuming the MCFK stems are made from prepreg carbon, then it's not hugely surprising - when laminating many layers of prepreg, it's difficult to be sure that no air is trapped between the layers. Any air that is trapped is really difficult to remove with so many layers - even when using vacuum + autoclave.

I don't think there's any chance at all that your stem will fail from these, but lets see what MCFK say.

Reliable void-free manufacture is one reason THM moved to resin transfer moulding for at least some parts.
i don't think they are voids from manufacture, they really look like cracks

tjvirden
Posts: 540
Joined: Sun Nov 22, 2020 9:21 pm

by tjvirden

They may be; one way of getting an idea is if you vary the torque on the bolts - starting from 0 and bringing them to 3Nm, do the fissures (neutral term) change at all? Wider/narrower etc?

The thing about the alloy supports that directly take bolt load is that they (should) prevent any bending load on the carbon at that point. If there's no bending load, only compressive, it's difficult to see how cracks could form - for cracks like that to form there needs to be a shear force.

But again, Lucendi states seeing something similar on a new stem.

elfuinha
Posts: 978
Joined: Sun Aug 08, 2010 10:18 pm

by elfuinha

So the Stem isn't within warranty, that i know, and acording to MCFK i will need to buy a new one.

Wasn't expecting this kind of expense now.

I will see what to do next.

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pritchet74
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Location: NorCal

by pritchet74

elfuinha wrote:
Mon Dec 13, 2021 7:43 pm
So the Stem isn't within warranty, that i know, and acording to MCFK i will need to buy a new one.

Wasn't expecting this kind of expense now.

I will see what to do next.
Well I wouldn't buy another MCFK stem. Personally, I am a huge fan of Extralite stems.
Have you ever wondered if there was more to life, other than being really, really, ridiculously good looking?

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Lucendi
Posts: 606
Joined: Fri Jul 19, 2019 10:37 pm
Location: Sweden

by Lucendi

elfuinha wrote:
Mon Dec 13, 2021 7:43 pm
So the Stem isn't within warranty, that i know, and acording to MCFK i will need to buy a new one.

Wasn't expecting this kind of expense now.

I will see what to do next.
If you really believe that the stem is damaged you should cut it in half or destroy it some other way.

I personally can't see anything wrong with it..

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micky
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by micky

Or you could ship it to Italy where I will gladly collect it. :mrgreen:

elfuinha
Posts: 978
Joined: Sun Aug 08, 2010 10:18 pm

by elfuinha

Lucendi wrote:
Mon Dec 13, 2021 5:26 pm
The lines you see are the different layers of carbon fiber that have separated/become delaminated.

I have two MCFK stems, one looks similar to yours and one doesn't. The one with the delamination I got brand new and came like that from the factory.

I wouldn't worry about it.
Can you send pictures of your stem. Thanks

by Weenie


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Juanmoretime
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Joined: Sat Jun 19, 2004 11:08 am

by Juanmoretime

I also have two MFCK stems in 100mm. One weighs 71 grams and the other 73 grams. I've had both for years and no cracks or issues. Did lubricate the bolts with anti seize and cabon paste on the carbon to carbon paste. 3mn of torque on the stem and handle bar bolts and no slippage. Love the stems!

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