Missing Link 11 Problem

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Bridgeman
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by Bridgeman

I've been using the KMC Missing Link with Campagnolo Chorus Chains for a while now, and have notice an issue that differs from using the standard Campagnolo Chain attachment pin method.

The problem I'm experiencing is chain skip on the 11 tooth Chorus cog. What I have discovered is the Missing Link is causing the skipping. It is the elongated portion of the link edge that is making contact with the spacer section of the cog. It is clear there is an interference there between the surface of the spacer section of the cog and the elongated slot portion of the Missing Link.

I wanted to post here and see if anyone else has observed this. If not I can take photos and also do a geometry study in cad and post results.

For reference, the cassettes, chains and Missing Links were/are new.

In the past, I've let the chain wear in and, over time, the skipping would stop. On older Missing Links I can clearly see the link edge wear at the contact point. Even with that small amount of wear, along with the wear marks on the 11 tooth cog, it was enough to provide adequate clearance that it resulted in ending the skipping.

On older used 11 tooth sprockets I have observed contact marks on the spacer portion of the 11 tooth cog. I've also taken a Dremel tool and provided clearance for the Missing Link by grinding small sections at the points of contact. By providing the clearance I could confirm that the Missing Link edge was no longer making contact with the spacer portion of the 11 tooth cog, and that the skipping was eliminated.

In my search, surprisingly, I have not found anything related to my observations. Looking forward to your comments.
Last edited by Bridgeman on Wed Feb 10, 2016 8:05 pm, edited 1 time in total.

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karmaz
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by karmaz

Running a couple of missing link 11 on a Chorus chains, no issues with skipping on either 12-25 or 12-29 across the whole range.
I've got an 11-27 on order, doubt that's gonna be any different.

Bridgeman
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by Bridgeman

The 12 tooth cog has more clearance, and would not be an issue. I hope your 11-27 is problem free when you get it.

Again, no mention of this topic in my search, yet it is happening on my 3 sets of wheels, all with new cassettes, chains and Links.

Frankie13
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by Frankie13

Running campy with missing link on 12-29 and 11-27 and shifting is as good as it gets. No issues here for years.

Valbrona
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by Valbrona

This observation doesn't surprise me one bit.

Here's what KMC would say if you raise this issue with them ' Thank you. Your comments have been noted'.

Bridgeman
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by Bridgeman

Did a little experiment today. I loosened the torsion spring adjustment on my Chorus rear derailleur for the least load on the chain. During a few sprints I could get the chain to skip at any point on the powerstroke. Then I tightened the torsion spring to midway. Now the skipping only occurs at the Missing Link. Lastly, I tightened the torsion spring full on. Now the chain only skips under an all out sprint, but will no longer skip during very hard riding.

Later this evening I'm going to Dremel the contact points on the cog. Since I've had luck with this fix in the past, I expect it will work this next time as well.

I don't think it's just a problem with the Missing Link end plate boundry interference as the cog spacer section outer diameter is contributing to interfering with the chain completely seating into the sprockets. I have a large selection of used 11 tooth cogs and ALL of them exhibit this pattern. Check out your stash and maybe yours might have the same contact marks. I'll try and take some photos as well.

When I take a new cog and wrap a chain around it I can clearly see the end plates touching the spacer surface. The chain is not fully seated like on a 12 or larger cog. Now add the extra offset with the Missing Link end plate and then that just makes matters worse, for me anyway.

What I do not understand is how no one else is having this problem.

Bridgeman
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by Bridgeman

Followup; The modification worked. No more skipping during full on sprinting today on hard training ride. Even set the rear derailleur to nearly most relaxed position, at about 5 to 10 percent, so less friction.

Will post pictures but need to set up email on my new phone first. I realize no one is having this problem, which completely baffles me, but thought I'd post about this issue just in case it comes up in the future.

I do recommend that Campy integrate chain end plate clearance on their 11 tooth sprockets, unless of course they like the idea of cogs wearing out faster than need be. I've seen these little buggers go for $95 a piece for the steel ones.

Oh, one last thing. I no longer think it is a Missing link problem, as it should not/can not be modified. Maybe in fairness to KMC I should change the title of this post?

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Calnago
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by Calnago

@Bridgeman: I like your tenacity in trying to get to the bottom of something. However, it sure sounds like a simple case of worn cogs and/or chain to me. The skipping you describe. Just how worn are the "used cogs" and chain you are experimenting with? (edit... just saw in your first post where you said everything was new). Have you tried the same thing with a brand new chain/cassette? But I am curious. I don't use missing links at all, but I do have a new cassette with an 11tooth cog handy as well as a new campy chain that I might try experimenting with to see if I can see what you are describing. What I think you are saying is that the chainlink outer plates ride on the ridge of the 11tooth cog that also acts as the spacer between it and the 12 tooth cog?
Also, what bike is this on... if you're going to supply pics, how about a closeup of the derailleur hanger as well. Is it within Campy's specs for hangers, specifically is it more rearward. Just wondering since you're playing with what I presume is the screw that allows the upper pulley to get closer or further from the cogs... the hanger specs can come into play there a bit as well.
Last edited by Calnago on Fri Feb 12, 2016 5:00 pm, edited 1 time in total.
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allencanna
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by allencanna

kmc chain is not that good.
i have one x11 unused in my box now.

Bridgeman
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by Bridgeman

Calnago, thanks for your very kind words. Yes, you are correct, "the chainlink outer plates ride on the ridge of the 11tooth cog that also acts as the spacer between it and the 12 tooth cog". The outer plates of the 11 tooth sprocket are riding on that ridge, rather than the rollers riding in the valleys between the sprocket teeth. I have many many used sprockets showing evidence of this, and some time ago I began modifying the sprockets to provide clearance which yielded new life to the cogs.

Because of the geometry of the Missing Link end plates, the elongated portion, this only exacerbated the problem.

I am still open to the idea that I could be overlooking something, but until that happens I think Campy needs to address this issue. Chains should not be rolling on their end plates as it is not the most efficient way to utilize them. All other cogs have proper clearance, as the chain rollers are engaged with sprocket valleys.

My hanger was checked a while ago and it was found to be in perfect alignment by a super Campy mechanic. Shifting is very crisp and reliable. The rear derailleur is a 2014 Chorus. The cassettes have well under 200 miles on it and the chain is new. I have 3 sets of wheels that are shared over the week and all exhibit the same skipping, except the recently modified one.

I believe the KMC Link is fine, as long as it has proper clearance on the cog ridge.

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Calnago
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by Calnago

@Bridgeman: ok, you had me curious enough to to do the kind of detailed study of this that you have done and I have not come to your conclusion. The 11 tooth "spacer channel" does not interfere in any significant way with a campy outer chainlink plate. If you "rock" the chain in a side to side motion the plate edge may barely touch that channel accounting for slight marks on the channel. However, when I press a single link down on the cog the interference contact is definitely the center roller and not the outer plate. Pressed square against the cog I can still see slight daylight between the channel in the cog spacer and the outer plate. Tried it with a section of new Shimano chain as well and same thing. So, this is simply not an issue as far as I can tell. Can't speak to the missing link plates as I've never used them but as far as a campy (or Shimano) chain is concerned it seems fine.
Below are the 11 tooth cog and chain sections I used to verify this. The 11 tooth cog is from one of the new 11/29 Campy cassettes. If I had more hands or an assistant that was anal enough to indulge me I would have taken a macro pic or two, but I've satisfied myself this is not an issue. I can appreciate however how you could come to your conclusion. The tolerance is very very close. But keep in mind that with any tension at all on the chain it will tend to pull that link up the ramp of the tooth thus increasing the gap between the plate and the cog spacer surface. When the chain eventually wears enough it can move so far "up" the tooth that it skips. But the plates on the campy or Shimano chains that I've tested would most certainly not be the cause of any skipping, at least in their current good condition (new).

Image

By the way, when I mentioned your hanger, I was more interested in its geometry. Specifically, whether it was more rearward than average or not (I'm assuming it's aligned), because if the hanger is on the long side and set back from the axle enough it could account for a less then really good engagement of the chain with the cog, especially the 11 tooth where only several teeth actually get engaged.
Last edited by Calnago on Fri Feb 12, 2016 9:26 pm, edited 1 time in total.
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thp
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by thp

I've ran into this issue with the KMC Missing Link. It was hit or miss depending on the link. When I went from a 12-29 to an 11-29 for the miss's bike I heard a different tapping type noise in the 11t. Thought it was adjustment, etc. Until I took the chain apart to inspect and installed a new missing link. Issue went away. The plates on the missing link had a bit of tolerance on the calipers, so it could just be a manufacturing thing.

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Calnago
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by Calnago

I don't have a missing link but it would be interesting if someone with a super accurate set of digital Vernier calipers could measure the max dimension of a missing link plate versus a standard plate on a campy or Shimano chain.
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Bridgeman
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by Bridgeman

Colnago, thanks for your observation and contribution. I've just done the same thing with a new chain piece like yours and while pressing the chain into the cog I can feel and interference as I rotate the chain link. I'm pushing on the chain such that it is loading squarely against the cog.

I'm still not able to load my photos yet, but I have clear evidence that contact is being made with a bunch of cogs. It took no time at all for the contact points to be visible on my new cogs as well. Maybe 2015 and newer cassettes have more clearance? My new cassettes are either 2013 or 14, not sure. Got them for cheap. The were cheaper than buying a single 11 tooth cog!

Apparently I spend a lot of time in the 11, so maybe that has something to do with the rapid wear marks.

Oh, the bike is an Felt F1 with their standard hanger. Not sure about the geometry as I haven't compared it to any others.

I do know that my mod has helped the situation, at least in my case as I'm back on the road.

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Calnago
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by Calnago

Try "folding" the chain so that you're only dealing with one single link and bushing. The only way I could get it to actually touch (and just barely) was to rock it side to side. It was definitely contacting the roller bushing first during all my testing. Ive never experienced even a single skip with a chain and cassette in good condition (and both Campy and compatible). Anyway, I've satisfied myself that at least with new 11sp Campy cassettes and Campy chains, that there's no issue. Oh, and you'll never be able to ascertain any of this with the chain and cassette on the bike, you would have to remove the 11 tooth cog, clean it, and then test etc.
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