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PostPosted: Sun Feb 02, 2014 8:09 pm 
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Posts: 713
I'm getting a drop chain on all gear 12 to 25 on the praxis small ring under load. FD is good, limit screw is ok. using an old KMC X11sl chain maybe about 1000 miles on them. replaced the chain with a low miles SR11 and it made a small difference but if you hammer it down and put all your weight on the pedal, still got a drop chain I don't even want to try standing up. also install the old KMC with 1k mile on my other bike with zipp crank and 10spd compatible rings and held pretty well and no chain drop. here's a picture of the small ring. what do you guys think.

Image

Image

Image

Image

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Colnago C50
2013 Colnago C59
2013 Cervelo S5


Last edited by nismosr on Mon Feb 03, 2014 4:49 pm, edited 2 times in total.

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PostPosted: Sun Feb 02, 2014 8:23 pm 
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Location: Welland, Ontario
looks not too bad to me. Seen a lot worse.

You say "dropping". You mean the chain is dropping off to the inside? Or what?

I'm guessing something else going on.

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PostPosted: Sun Feb 02, 2014 8:28 pm 
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Have you thought about getting a chain catcher?


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PostPosted: Sun Feb 02, 2014 8:33 pm 
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bikerjulio wrote:
looks not too bad to me. Seen a lot worse.

You say "dropping". You mean the chain is dropping off to the inside? Or what?

I'm guessing something else going on.



Yes inside, under load or when you hammer it down hard.

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Colnago C50
2013 Colnago C59
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PostPosted: Sun Feb 02, 2014 9:06 pm 
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Location: New York
There is nothing wrong with the chain ring. You'll need to either adjust the limit screws, check chain length, front derailleur shift throw or crank/chain alignment.
Check the difference in chain alignment with the 2 cranks.

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PostPosted: Sun Feb 02, 2014 10:59 pm 
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stella-azzurra wrote:
There is nothing wrong with the chain ring. You'll need to either adjust the limit screws, check chain length, front derailleur shift throw or crank/chain alignment.
Check the difference in chain alignment with the 2 cranks.


how do you check crank/chain alignment ?

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PostPosted: Sun Feb 02, 2014 11:03 pm 
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Posts: 183
Campy FD? Did you set up the FD from the top down like how the park tool website describes? If so that's probably what's going wrong.

Try setting it up from the bottom up, then eliminate the last lever stop on the shifter with the limit screw. You don't need the 4th stop.

I had the same issue, not once since setting it up that way.


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PostPosted: Sun Feb 02, 2014 11:21 pm 
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Ed, make sure the small ring is not on backwards (I doubt it is but worth checking anyway). A few other things worth checking: Place the chainring on a glass surface and check to see if it is bent. How much clearance do you have between the outer rail of the FD and the chain (when shifter is at zero)? Also check to make sure that the FD is parallel to the chainring -- if the tail end of your FD is closer to the chain, it may push the chain off when the chainring flexes under load.


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PostPosted: Mon Feb 03, 2014 1:08 am 
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audiophilitis wrote:
Ed, make sure the small ring is not on backwards (I doubt it is but worth checking anyway). A few other things worth checking: Place the chainring on a glass surface and check to see if it is bent. How much clearance do you have between the outer rail of the FD and the chain (when shifter is at zero)? Also check to make sure that the FD is parallel to the chainring -- if the tail end of your FD is closer to the chain, it may push the chain off when the chainring flexes under load.


Tim,
this is the clavicula/praxis that was on my SLR01 which I never had a problem, noticed this yesterday on my first ride with the R5 it happen several time on the first couple a miles and I decided not to continue on the ride with Eric.

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2013 Colnago C59
2013 Cervelo S5


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PostPosted: Mon Feb 03, 2014 1:19 am 
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also wanted to add a test I did
I have the chain on the small ring and maybe on the 16/17 cog, I position the bike against a wall, front wheel on the wall. crank arm on 3 o'clock position and clip on the pedal, as soon as I push down half of my weight like pedaling forward the chain drop instantly.

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2013 Colnago C59
2013 Cervelo S5


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PostPosted: Mon Feb 03, 2014 2:04 am 
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Location: New York
nismosr wrote:
stella-azzurra wrote:
There is nothing wrong with the chain ring. You'll need to either adjust the limit screws, check chain length, front derailleur shift throw or crank/chain alignment.
Check the difference in chain alignment with the 2 cranks.


how do you check crank/chain alignment ?


Read this http://www.parktool.com/blog/repair-hel ... e-concepts
See if this helps you out

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PostPosted: Mon Feb 03, 2014 2:26 am 
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Is there any play in the crank? This seems like a FD or bent ring issue as others have suggested.

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PostPosted: Mon Feb 03, 2014 5:15 am 
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Posts: 440
nismosr wrote:
also wanted to add a test I did
I have the chain on the small ring and maybe on the 16/17 cog, I position the bike against a wall, front wheel on the wall. crank arm on 3 o'clock position and clip on the pedal, as soon as I push down half of my weight like pedaling forward the chain drop instantly.


Post some pictures of the front derailleur in this position. Side view, chainline view, and top view would be helpful.


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PostPosted: Mon Feb 03, 2014 5:31 am 
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bombertodd wrote:
nismosr wrote:
also wanted to add a test I did
I have the chain on the small ring and maybe on the 16/17 cog, I position the bike against a wall, front wheel on the wall. crank arm on 3 o'clock position and clip on the pedal, as soon as I push down half of my weight like pedaling forward the chain drop instantly.


Post some pictures of the front derailleur in this position. Side view, chainline view, and top view would be helpful.


Thanks
will do it tomorrow ..

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2013 Colnago C59
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PostPosted: Mon Feb 03, 2014 8:11 pm 
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Posts: 965
nismosr wrote:
also wanted to add a test I did
I have the chain on the small ring and maybe on the 16/17 cog, I position the bike against a wall, front wheel on the wall. crank arm on 3 o'clock position and clip on the pedal, as soon as I push down half of my weight like pedaling forward the chain drop instantly.


The chain really should be engaged on the teeth of the small chainring and not come off regardless of what else might be happening, as long as you aren't moving the chain onto the ring.

The rear derailleur couldn't be doing this, nor really could chain tension or length. And this isn't happening during a shift so as long as the front shifter isn't really pushed against the chain, you can rule out the front shifter.

Long shot is really bad chain line, but even that would be hard to imagine. Are you sure that the chain sat down fully on the small ring and was fully engaged into the teeth? If you were shifting down onto the small ring and it wasn't fully engaging, you could be getting torque at low power but the chain would spin free and likely fall inwards if you put more pressure on it. I might have said a very very badly worn chain but you've addressed that. So I'd set it up and be sure the chain is all the way down onto the ring. It's the only obvious thing I can think of that could be causing your pattern of chain drops. It's not uncommon with that setup for the chain to shift down from the big ring and not seat fully on the small ring. Then that can in turn be caused by front shifter adjustment, by chain line, or a couple common issues. But the chain shouldn't pop off if the ring isn't turning and the chain is fully engaged.


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