Shifting into the small chainring throws off chain at RD

[istigatrice]

I think the earlier misstatement may have thrown people off in the diagnosis

Apologies for the mis-leading post. I must have gotten it confused when I first started the topic. Hope all confusion has been cleared up by the pictures.

I'll see if I can get around to getting a photo of the small small combo soon, but just wondering, how does one check the chainline?

Also, is it ok to disassemble the RD body without breaking the chain?

Thanks for the most helpful advice.

[martinko]

I don't know how to check it. I suspect chainline because I also ride Rotor cranks, and, in my case, the chain is very noisy when on the big ring and smaller cogs, or skips when pedalling backwards. I tried to tweak the RD, but without success. I assume I have also problem with chainline.




Possible solution is to take the cranks out, and remove (or add) 0.5mm spacers, either on DS or NDS, and see whether it helped. I plan to do it, but I am little bit lazy and lack time when I am near my bike, I rather ride it.

[dwaharvey]

Yes, that's the b screw. Having seen these photos though, I agree that hanger misalignment (twisted about vertical axis) is the most likely cause.
You can take the cage apart without breaking chain, but it is more fiddle that way (and you'll want to take chain off front rings to eliminate tension on it)


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[istigatrice]

Just thought I'd give this an update:

I pulled apart the RD cage today, and it was ever so slightly twisted (compared to a flat surface). I've twisted it back so that the screw holes for the jockey wheels sit flush with a straight surface.

What surprised me more was that the RD hanger was also twisted. I straightened this as well. Not sure how it would have gotten twisted, but obviously contributed to the problem.

I tested a few downshifts, which worked fine... a few of them looked like they were about to drop the chain, but it righted itself almost instantly - if I wasn't looking right at the jockey wheel I wouldn't have noticed. Time on the road will tell if I've fixed the problem.

Also, not sure if this affects the problem, but I also had to tighten the b screw even further. to prevent the jockey wheel from rubbing on the cassette after the straightening.

Finally, I also tried to get a measurement of the chainline, but I didn't have tools to do this accurately (a see through ruler isn't the best tool on a black bike). I was getting a chainline of between 44mm with an uncertainty of 1mm, which is within error to what sheldon suggests with 43.5mm.

[istigatrice]

Oh, and here's a picture in the small small combo for those who want to verify my chain length.



The gap between the chain and the bottom of the rear mech is about 1cm.

[bikerjulio]

2 things:

I know you said earlier that the hanger was bendable, but I'd still be ordering a replacement hanger from Wheels Manufacturing. Recheck alignment with a proper tool. Alloy hangers can be brittle and not take well to being straightened. Mine spontaneously let go with unpleasant results. A hanger failure could easily cause a catastrophic accident when the RD goes into the rear wheel.



The chain is 1 link too long, although it's not the cause of your problems.