Shifting into the small chainring throws off chain at RD

[FIJIGabe]

Can you take a photo of the complete RD mechanism, including the tension screw? What component group are we talking about? It may be 2500km, but what kind of conditions are you riding in? A lot of mud/dirt? What's your cleaning regimen? I've heard of chains being worn out that quickly, you may be unlucky in that sense (also, where did the shop measure the chain?).

What I'm thinking here is that when you move from the big ring to the small ring, you are dropping more tension on the chain than the RD can pick up (limit screw too far in, chain too long or stretched). What gears are you running up front? Are you running a matched set of rings, or some sort of Franken-gear (like a 53/34)? I've got more questions than you've provided me answers to.

[istigatrice]

Hi guys, thanks for the ideas with try and get better photos tonight.

Groupset is shimano 105 5800 running 52/36 rotor noq chainring with an 11/28 on the back.

Cleaning regime is fairly slack, but I've been slacker on ultegra groups and older 105 groups and it hasn't been an issue...

Chain is being thrown off onto the inside of the jockey cage, the side closest to the wheel.

[Calnago]

Another question: was the whole bike including the groupset brand new when you bought it? Was there ever any other group on the frame that seemed to be working just fine before this one?

[istigatrice]

Frame and groupset were purchased new. They worked fine for the first thousand or so km. Started playing up in the second thousand.

One other thing, if I pedal backwards the chain aligns itself on the jockey wheel. I'm 100% sure the chain is on the right way though. Would anything else cause these symptoms?

The only other thing I can think of which might cause this would be the chaline of my rotor cranks. But I'm sure they're plenty of people using this crank so I doubt it's chainline.

[dwaharvey]

Also check gap between upper pulley and the cassette through your gear range. If the b screw is too far out and the pulley's movement is affected by the cogs, it might cause something like this. Because the pulley's axis is behind the pivot of the cage, it will tend to move up when the cage arcs back, as will happen when you shift down in the front...
Also does the rear cog choice affect it happening? Does it stay on if you are in one of the bigger rear cogs?
Can you get it to happen on a stand, or only when out riding? If you can duplicate in on the stand, it ought to be easy to diagnose by watching carefully how it proceeds.


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[istigatrice]

Hi, thanks for the suggestion.

I can get this to happen on a stand, When I am in my 28 or 25 is will regularly get caught in the cage. When I'm in the 23 and change it happens much less frequently. I didn't think twice about this because I thought it would have to do with angle?

[dwaharvey]

You said it comes off to the inside, so it seems unlikely the chain angle is the cause if it happens more easily in one of the biggest cogs (when the chain is angling out from the rear...if due to angle it seems more likely it would come off to the outside)...
Check the b limit screw and make sure there's always more than about 12mm of space between the pulley and the cogs when in those gears.
And put it in the stand in the 52-25, shift it down on the front while turning the crank very slowly, and see what you can tell about how the (faulty) shift develops....


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[mattr]

But I'm sure they're plenty of people using this crank so I doubt it's chainline.

There have been a few posts cropping up on here (and other forums) regarding rotor chainline issues.......... but, this doesn't sound like a chainline issue.

[mattr]

And you are shifting 52=>36 whilst running in your 28 and 25 sprockets and wondering why the chain is doing weird things?
The mech is near its full extension, being pulled off line, then taking up all that slack, in one go..........

Might be worth aiming for an earlier downshift, on the 23/21 for instance.

[martinko]

I really don't know how but I would suspect chainline to be wrong. If you have any other compatible crankset+BB lying around, try swap it.

[istigatrice]

OK so took the advice of trying to replicate this chain drop slowly. From what I can see, the chain shifts perfectly, and once it's on the small ring the chain "jumps" off the RD :



As you can see the chain is thrown off onto the right side of the jockey cage. Not sure where to go from here.

And @dwaharvey, is this what you mean by the b limit screw (the one pushing against the RD hanger)?

[Wonderman]

Definitely check the chain line, I had almost the exact same issue with da9000 and a sisl2 crank, in the end I had to remove the non drive side space and put it on the driveside to fix the issue, it only
Happened to me when I was in the big ring up front and the rear largest cogs

However when I moved that set to another frame I put the spacer on correctly and it was fine

[em3]

OP, you indicated shop verified that chain length was OK, but yet, they let you leave the shop without addressing this issue? If this is the same shop that aligned your hanger, I would be suspect of their expertise. Here are some things to check again, in priority order:
1. hanger alignment (yes, I know u said you, or shop, checked alignment, but making sure that both VERTICAL and LATERAL axis are correct is crucial ....you would b surprised how many people only check vertical alignment).
2. chain length (post a pic with your chain on small/small combo so group can access your chain length)
3. B-screw...looks like your b screw is nearly topped out at max insertion, letting it out a few turns and moving your upper pulley closer to cassette might help
4. snagged or bent teeth on your chainrings...you mentioned the issue is more consistent on two upper cogs, where your chainlink is most extreme and where even a slightly bent tooth can result in a snag that causes the chain to jump... would check for bent teeth on cassette too

Given that this issue just started happening and your bike was working fine before and assuming that there were no adjustments/changes made to parts which could have caused he issue, I am going to double down on bent hanger. EM3

[TheKaiser]

OP, earlier in the thread you said "Chain is being thrown off onto the inside of the jockey cage, the side closest to the wheel." But your more recent post says "As you can see the chain is thrown off onto the right side of the jockey cage." and the photos confirm it. Assuming that the problem does not vary from side to side, then I think the earlier misstatement may have thrown people off in the diagnosis. Given the new info, it doesn't seem as mysterious as it did at first. Definitly re-check the hanger, and chainline as others have said, look for any twisting of the derailleur cage vs. the plane of the bike, and consider subtly "tweaking" the derailler as a last resort before replacing.

One thing I haven't seen mentioned though is to take a close look at the outer derailleur cage plate. I have had them bend in a sort of "spreading" manner or little tabs even break off of them so that they don't sit as close to the pully as originally designed. This usually has happened from a sort of uncommon incident, like a stick in the spokes or or something. Here is the thing though...once it gets bent then it can cause problems all the time, like you have, as the cage effectively should act as a chain guide, restraining the chain to a degree. Once it gets spread apart a bit, it can no longer prevent minor misalignments from becoming major derailments, which is exactly what yours seems to be doing. Each further derailment may bend it a bit further worsening the problem. This could also explain why the problem only occurs in that one shifting scenario, as the part of the pully and cage that the chain interacts with is different than when the chain is taut as in a big-big cross gear, which would typically cause this sort of thing, but doesn't in your case.

I tried to get an idea of if your cage might be bent/spread outward in the photo but it was tough to tell because the chain was jammed in there too. The best way would be to take the inner cage and pullys off and use a flat plate to check everything for square.

I hope that all makes sense...its late and I need to sign off so no time to edit!

[PSM]

Have you ever removed the lower jockey wheel for cleaning? If so, it have to be mounted correctly.
It is written on it which side that shot be facing outward.