Chain issues, What's going on here?

[Tom B]

This has happened on my commuter a couple of times in the last couple of days...

It always seems to happen at speed when picking up pedaling from free wheeling. The chain over shifts off the big chainring and does this. The only way to get the loops out is to work them together with much getting oil everywhere and finger pinching.The road was pretty rough, but not excessive.

There does seem a bit of a lack of chain tension, but there always has been on this bike and the chain does rattle and slap around. The front deraileur is adjusted to the point that it does shift up nicely but just to the point it doesn't rub when in the smallest rear sprocket.

After the first couple of times it did it I gave the chain a clean and lube as i find most of my shifting problems are due to lubrication.

I suspect that the chain is stretched to the point of needing replacement (my measuring tool is at work so haven't measured) it won't be excessive, i've certainly used chains with more wear.

The chain looks embarrassingly dirty but in my defence i cleaned it yesterday and at the point of photo it had done 35miles on damp leafy dirty roads. I think the wet lube look doesnt help - its black when it goes on.

 

[Geoff Crowther]

Oh dear. Sorry, nowhere near clever enough to help but I'm looking forward to seeing the answer.
Stiff links?
Good luck!

 

[sight-pin]

Could it be your bottom bracket is loose, I found mine loose and noticed, when i pushed hard down on the right pedal, i could see the top of the large gear tilting to the right. A quick tighten cured the problem in my case.
So i'm just wondering if that is causing your chain to jump off the large onto the smaller cog? as for the condition of the chain, i would probably fit a new one.

 

[Cycleops]

Obviously an issue with the chain, if you've tried luring and that doesn't work I should just get a new chain. For a tenner or so it should sort it.

 

[Tom B]

Obviously an issue with the chain, if you've tried luring and that doesn't work I should just get a new chain. For a tenner or so it should sort it.

New chain is the plan for the end of the week... i just cant help wonder about the chain tension issue...?

 

[Cycleops]

New chain is the plan for the end of the week... i just cant help wonder about the chain tension issue...?

If too slack this may be caused by the worn chain, so the new one should sort it.

 

[Nigelnaturist]

if the chain is slack its also possible the tension on the RD is weak, but as that looks a newer modal of the Acera than the one I had it's unlikely.

 

[Tom B]

A long time ago, I know, but for archive purposes.

I fitted a new chain and cassette as in the days that followed the chain started jumping and slipping on the cassette.

The problem was solved, the new chain was surprisingly a link or shorter (in number as well as overall length)!

Now the chain has had a thousand miles or so to bed in the problem of the big ring over-shifting has returned has has a propensity for the chain to get dumped off the smallest cassette sprocket, so i am guessing that the stop on the biggest ring is set marginally wide and the RD set a bugs dick low and these problems only show when the chain has a bit of wear and wander. Ive nudged the settings but the issue was so marginal that i can't reliably reproduce the fault on the stand.

if the chain is slack its also possible the tension on the RD is weak, but as that looks a newer modal of the Acera than the one I had it's unlikely.

I have no idea how well respected the RD is, but i have to say it is one of the best i have ever owned. Easy to adjust, precise and responsive. The chain slap issue and thus seemingly tension issue cured by new and slightly shorter chain.

 

[zacklaws]

That's a good mystery, makes a change from hunting for clicks and rattles, Out of curiosity tried to emmulate it on one of my bikes by hand, but could not get enough slack in the chain to create those two loops, but I never tried it, small chain ring to small sprocket. Some how I get the feeling, the chains too long and maybe some chain suck involved or the bouncing about on the road. It might be helpful to post some pictures of the drive train without the loops in the chain then people may see better if the chain is too long

By overshift, do I presume the chain comes off the chain ring on the crank side or drops back down to the middle ring which is undershift (I think)

If you do not have a stand, hang your bike from the washing line as I do for quick adjustments on the gears and then see if you can replicate it happening or starting to happen as you turn the cranks fast as you go through the gears