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PostPosted: Sun Aug 31, 2014 5:01 am 
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Joined: Tue Feb 05, 2013 11:53 pm
Posts: 103
Hi Fellow Weenies,

I had my bike assembled a few weeks ago. Since I moved to a new city, and I have a baby at home, it is being a bit hard to ride frequently. I have rollers, and I am using them a bit more often.

The FD shifting was never as good as I expected, and in the last few days, something really strange started to happen: when I shift from the big to the small ring, the chain does not actually "engage" to the small ring:

Image

I tied to troubleshoot, and I found out that the LBS did not install the aluminum mount plate, so the alignment screw was touching directly the CF seatpost. I installed the plate, and follow all the instructions to adjust the FD, but the problem persists

The bike is a NeilPryde BuraSL (Pressfit30), with a Rotor 3D+ / P2M crankset. I am using Praxis 52/36 rings (they came from my previous bike, and they have around 1500 km). Chain is KMC X11SL. FD & RD are DuraAce Di2 (RD is working fine).

Any idea of what might be be the issue?


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Posted: Sun Aug 31, 2014 5:01 am 


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PostPosted: Sun Aug 31, 2014 9:28 am 
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Joined: Thu May 27, 2010 2:36 pm
Posts: 29
I have experienced the exact same on my Rotor 3D+ P2M on an old set of Q-Rings with too much offset so the chain could go between them. Changed to new type Q-rings with less offset and never experienced it after. This was with Di2 as well.

So not sure this is an Di2 problem.


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PostPosted: Wed Sep 03, 2014 12:19 am 
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Joined: Tue Dec 18, 2012 1:31 am
Posts: 23
Looks like your lower limit screw is too far in, stopping the mech moving far enough in to drop the chain onto the ring. Full installation instructions here: http://si.shimano.com/php/download.php? ... 04-ENG.pdf, see page 55.


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PostPosted: Wed Sep 03, 2014 12:43 am 
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Joined: Tue Feb 05, 2013 11:53 pm
Posts: 103
Thanks! I followed all the instructions from Shimano. The positions seem fine, but it still does not shift well.

Since Teletori mentioned a similar behaviour with P2M, I contacted them, and they contacted Praxis. It seems it might be an issue with the inner ring, and I will try a new one.

Nicolas, from Power2max, is again providing excellent customer service.


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PostPosted: Wed Sep 03, 2014 1:13 am 
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Joined: Tue Apr 22, 2014 2:17 am
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Just a tip, I would recommend getting rid of that little metal plate you attached to the frame, as when it falls off (and I promise it will!) it will screw up your shifting, and if it happens to fall off during an event/race you will be very sorry!
I have not seen a single Di2 pro bike built using that metal piece yet, and we never use them at my shop either!

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PostPosted: Wed Sep 03, 2014 1:37 am 
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Joined: Tue Feb 05, 2013 11:53 pm
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In fact it felt at home, minutes after I glued it. I glued again with double sided tape and it is holding.

I decided to use it because I could not get descent shifting with the low/high screws only. But it is true that now the screw is just touching the plate. Once i get the new ring I will test it without the plate


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PostPosted: Thu Sep 04, 2014 12:11 am 
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Joined: Wed Feb 19, 2014 6:13 am
Posts: 46
fancycoconut wrote:
Just a tip, I would recommend getting rid of that little metal plate you attached to the frame, as when it falls off (and I promise it will!) it will screw up your shifting, and if it happens to fall off during an event/race you will be very sorry!
I have not seen a single Di2 pro bike built using that metal piece yet, and we never use them at my shop either!


How does this plate fall off when the mild adhesive is not what holds it on - but rather proper use of the support bolt.
Just curious, as I have built/sold/seen ridden too many bikes to count and never seen a missing plate after being built with it.

The issue OP has probably has nothing to do with Di2 - unless the low limit is drastically over-tightened, the issue is ring spacing, chainline, or incompatible wear between chain/ring...


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PostPosted: Thu Sep 04, 2014 11:08 am 
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Joined: Fri Jan 09, 2004 6:38 pm
Posts: 89
Location: France
How old are your rings ?
Maybe your rings are 10sp rings ?
Rings manufacturers had to change slightly the distance between small and big ring since 11sp chain is thinner and can fall "in between" the rings when shifting from big to small.

I'm riding so 10sp rings on my 9070 Di2 and it works "good enough" but it does happen from time to time (mostly when shifting at slow speeds / slow cadences) and I know the reason. Since I use 50/34 only for the summer when riding in the Alpes I didn't want to buy 11sp rings just for a few weeks but I did experience what you experience. Don't have the problem with 11sp compatible rings I use the rest of the year.

Maybe check if your rings were 10sp rings or the new 10/11sp type ?


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PostPosted: Thu Sep 04, 2014 12:24 pm 
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Joined: Wed May 24, 2006 6:25 pm
Posts: 1401
Your chainringbolts are tight, right?

As others have said, the FD is not the issue. It's a chain/chainring/crank issue. By adjusting the FD carefully, you can decrease the odds of it happening, though. Madcow had some great ideas in a thread over at the old Fairwheel Forum. I wish my memory was better, but I think the best fix was bending the rear end of the outer cage in a bit, but as I said, that just works on the symptoms.

If you search for "chain skating", you'll find a lot of people who've seen this. When I've seen this in person it has always been on chainrings with a 16t jump, I've never seen it on a 53/39.

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PostPosted: Thu Sep 04, 2014 12:48 pm 
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Joined: Thu Mar 28, 2013 4:42 pm
Posts: 116
Location: Pa USA
Happened to me for the first time yesterday, I run 52/36-but have been for a year, and have only had the one instance.

As far as the metal plate goes, I didn't use mine, but the screw is hard against a metal derailleur hanger plate, if it was against carbon I would certainly, positively, without a doubt use it. And I agree, if its under heavy screw pressure I don't know how it's likely to fall out.


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PostPosted: Thu Sep 04, 2014 12:55 pm 
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Joined: Tue Feb 05, 2013 11:53 pm
Posts: 103
Praxis believes it is a bad inner chainring, and they are sending a new one.

The faulty one was a 10/11 sp version and the chainring bolts were torqued to 8Nm. It was used for ~1500 km in my previous bike.

I doubt this is a chainline as the set-up is fairly standard and I am using the spacers as indicated by Rotor.

Anyway, I am waiting for the new ring to arrive and I will report back.

Thanks for all the suggestions


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PostPosted: Thu Sep 11, 2014 1:22 am 
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Joined: Tue Feb 05, 2013 11:53 pm
Posts: 103
Just a follow-up. The issue was actually on the inner chainring. I have just replaced it and it is shifting perfectly.

The strange thing is that these same rings were working fine in my previous bike (10sp DA Di2). Not as smooth as it is now, but with no "skating".

Thanks for all the tips here. Nicolas from P2M was also really helpful, as usual.


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Posted: Thu Sep 11, 2014 1:22 am 


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