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PostPosted: Mon Aug 31, 2015 6:27 pm 
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Joined: Tue Jul 02, 2013 2:34 pm
Posts: 25
Your experience and ideas needed!

I'm having a really scary issue with my new (otherwise beautiful) carbon stem. It's a 90mm MCFK stem and I'm experiencing extreme slippage, like the bar dropping 90 degrees when I brake semihard. Holding the hoods I'm diving forward, really scary when going fast. Bar is Ergosum LTD if that matters.

I've been to my LBS to get Carbonpaste and the correct nm settings (3nm at bar, 5nm at fork).

Not sure what to do.... :( Only tip i got of google was skateboard tape, not sure if that is too great with a carbon stems though, any ideas? I'm 74kgs, if that helps.

Cheers!


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PostPosted: Mon Aug 31, 2015 6:35 pm 
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Joined: Thu Dec 09, 2004 1:57 pm
Posts: 251
I've used carbon paste and it helps quite a bit, but 3nm at the bar seems low. 4-5nm seems the norm for most carbon stems I've used.


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PostPosted: Mon Aug 31, 2015 6:37 pm 
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Joined: Wed Oct 17, 2012 12:42 pm
Posts: 51
Did you try to put some loctite on the screws of the stem when fixing with the right Nm?
I experienced that the screws loosing during riding on cobbles and my handlebar dropped down :(


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PostPosted: Mon Aug 31, 2015 6:51 pm 
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Posts: 25
I have not tried loctite no. I was getting slippage riding carefully on flawless asphalt though. I can't imagine the screws slipped out that easily?

3nm is max recommended settings for the front for this stem.


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PostPosted: Mon Aug 31, 2015 7:03 pm 
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Posts: 1904
5-6 N*m is a more typical stem torque. I have had no problems with slippage using carbon bars and 3T, Ritchey, Easton, VCRC, and Thompson stems, so I think your stem is "the problem".


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PostPosted: Mon Aug 31, 2015 7:14 pm 
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Location: NorthEU
Don't overdo the torque. Change stem. It's not worth those grams.
I used Extralite Hyperstem and it cracked two expensive forks for me and no-one give warranty.
This was forks for 1550 Euro so i am not happy.
I would never use that stem. Just face it, it is not working with your bar - change it!

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PostPosted: Mon Aug 31, 2015 7:45 pm 
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350euro stem in the garbage huh? Gonna try at least something else b4 I go that route. Berk Combo might be a way out unless nothing else works...


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PostPosted: Mon Aug 31, 2015 8:24 pm 
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I'd measure the stem and the bars with a micrometer to see if one or the other is out of spec. If it's the stem them I'd contact the manufacturer.

I think most manufacturer size bars/stem to 31.75mm but bars/stem are often spec'd as 31.7 or 31.8. I could imagine a slippage situation where a stem is 31.8 and bars are 31.7.

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PostPosted: Mon Aug 31, 2015 8:32 pm 
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Is that a 4 bolt stem? Even at 3nm you shouldn't be getting that kind of slippage. I use 4nm for most stems. The 3T bar also has a good anti friction coating on the stem clamp area. Whatever the cause, that combo is not working and you shouldn't have to resort to shimming, or skateboard tape to compensate. Like someone said, take some calipers to the bars and if they are in spec, then return the stem. It's new, and that's not right. You did tighten the bolts gradually I presume, as opposed to tighten one all the way down to 3Nm before even starting the other one?

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PostPosted: Mon Aug 31, 2015 8:34 pm 
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Location: United Kingdom of Great Britain and Northern Ireland
Most bikey sizes are taken direct from Imperial. 1 1/4" = 31.75mm. While you can certainly measure the bars, you cannot really measure inside a two-piece stem clamp.

I would use carbon paste and some judicious tightening of the stem bolts to 4/5 Nm, and then if there is still slippage something ain't right.


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PostPosted: Mon Aug 31, 2015 8:58 pm 
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Joined: Mon Sep 07, 2009 3:10 am
Posts: 403
The first thing that people misunderstand is the torque, just because most of the stems that people use allow for 4nm at the stem does not mean that you can use 4nm. It is a carbon stem, you need to use the torque that the manufacturer recommends. If they had intended 4nm they would have specified 4nm.

They tested the stem and specify 3nm so you have to use 3nm. Generally you can go over a few percent but you will break the stem if you go much over 3nm.

I recommend using tubular glue, Vittoria Mastik'One is my recommendation. Put the glue both on the stem and center of the handlebar and try not to make a big mess. Let it sit for a few and clamp the stem down at 3nm and see if that holds better. I would recommend using a good torque wrench and after tightening to 3nm, let it rest and come back and torque it again. Sometimes the carbon and glue will relax.

I would not recommend using Loctite on the screws, not a big deal if you have used it, clean off the old Loctite. If you use Loctite, the Loctite hardens and makes the screw more difficult to tighten and then you are not really getting the intended amount of tightening. Your problem is not with the screws coming loose.

If you decide that you don't like the tubular glue, use goo gone and it will all come off. Use goo gone to clean up any mess that you have on your handlebar. You don't need a ton of tubular glue, if you put too much then it will squeeze out the side so not a big deal. It will take a couple of days to dry inside the stem/handlebar and get to full strength. It still might slip if you hit a big enough pot hole but it should do the trick.


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PostPosted: Mon Aug 31, 2015 9:08 pm 
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Agreed, if they say the Max torque you should use for that stem with the bolts supplied is 3Nm, then for sure don't go over that. However, resorting to glues and tapes etc to take up a tolerance gap in something as critical as your bar/stem interface is just wrong. If it doesn't clamp properly at the max torque of 3Nm then by all means return it, especially since you said it was new.

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PostPosted: Tue Sep 01, 2015 2:24 am 
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Posts: 444
I have the MCFK and know exactly what ur talking about..

add a small layer of carbon paste to the clamping area and faceplate, align bars, reattach faceplate w/o tilting bars while tightening and u should be golden

You can go over 3Nm....3 is way to light... can get closer to 5 w/o any issues but def would not go over.

Hope this helps.

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PostPosted: Tue Sep 01, 2015 7:42 am 
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Did you use carbon paste already?


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PostPosted: Tue Sep 01, 2015 8:53 am 
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Did you read what the op wrote?

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