Chain going beside rather than round lower jockey wheel - why / how fix?

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frank9755
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Re: Chain going beside rather than round lower jockey wheel - why / how fix?

Post by frank9755 »

Thanks for comments and questions

It's Ultegra 6870 Di2: I built the bike up in 2015.

It happens on the workstand as well as if I ride it.

It's not the hanger (as mentioned in the OP): I changed it and it made no difference. The old hanger I took off was perfectly straight.

So looks like two possibilities:
- The cage could be bent but I don't know how that happened, and I'd rather rule out other possible causes before I mangle it!
- I may well have the wrong wheel on the bottom as I recall they both looked the same to me when I changed them (my error, not LBS!). I'll investigate this. However, the problem started before I changed the jockey wheels (it was why I changed them), so suggest the cage might be more likely....

I'll report back when I've had a look at the jockey wheels.
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frank9755
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Re: Chain going beside rather than round lower jockey wheel - why / how fix?

Post by frank9755 »

OK, I think I've got it.

I looked at the jockey wheel and I had the right one at the bottom, but it was the wrong way round. I've flipped it and, a quick ride up and down the street with 20 shifts, and it is staying on.

I'll do a decent test ride over the weekend to check for sure.

Thanks everyone for thoughts.
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cycleruk
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Re: Chain going beside rather than round lower jockey wheel - why / how fix?

Post by cycleruk »

Over recent years bottom jockey wheels have an arrow on them to show rotation direction. I don't know why they have to be but when I got one wrong it was certainly noisier than it was when corrected.
I think you'll find the teeth are chamfered slightly more on one side ?
You'll never know if you don't try it.
cyclop
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Re: Chain going beside rather than round lower jockey wheel - why / how fix?

Post by cyclop »

frank9755 wrote: 30 Jul 2021, 6:43pm OK, I think I've got it.

I looked at the jockey wheel and I had the right one at the bottom, but it was the wrong way round. I've flipped it and, a quick ride up and down the street with 20 shifts, and it is staying on.

I'll do a decent test ride over the weekend to check for sure.

Thanks everyone for thoughts.
Excellent!! Observation,collective knowledge,solution.
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Mick F
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Re: Chain going beside rather than round lower jockey wheel - why / how fix?

Post by Mick F »

Well done! :D
Who'd have thought that a jockey wheel the wrong way would cause it?



Still mystified how it could happen that a chain could sit besides the bottom jockey.
Just been doing some measuring with spare mechs and a spare chain.

Campag chain 10sp. Never used anything different for years.
The chain is 5.9mm wide across the pins.

Campag Chorus 10sp rear mech at the bottom of the cage is 9.5mm wide.
This means that there is only 3.6mm either side of the centre-line of the jockey ........... therefore no room for a chain to de-rail off the jockey.

My measurements don't include the thickness of the jockey teeth, so there's even less room.

Shimano XT Deore 9sp rear mech. (same geometry as 10sp so indexes fine with 10sp)
Same chain at 5.9mm but the cage is a little wider at 9.8mm at the bottom.
This means that the space still isn't wide enough for the chain with 3.9mm available.

It just can't happen, so I'm still mystified.
Mick F. Cornwall
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frank9755
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Re: Chain going beside rather than round lower jockey wheel - why / how fix?

Post by frank9755 »

Thanks Mick!

It's surprising that there is enough room. I've just measured the cage width at 8.8mm for an 11 speed shimano chain at 5.4mm so, if anything, there is slightly less space than you have

When it was off, the chain was right up on the shoulder of the jockey wheel teeth, and maybe pushed it over slightly. I guess it must have done or there wouldn't have been room.

Looking at it again the cage is asymmetric, there is at least a mm more space on the is outboard side, where it was falling, so that will have helped a bit.
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Mick F
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Re: Chain going beside rather than round lower jockey wheel - why / how fix?

Post by Mick F »

No experience at all of 11sp, so can't really put any thoughts across about it.
I just know that my 10sp stuff cannot de-rail off the bottom jockey as there's no room at all.
Tried it, but it can't happen.

Main thing is, you've sussed it! :D
Good info. :D
Mick F. Cornwall
gxaustin
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Re: Chain going beside rather than round lower jockey wheel - why / how fix?

Post by gxaustin »

Are the idler wheels Shimano 11 speed? Could you have been given the wrong ones with wider spacers?
there is a 2.2mm maximum gap between the edge of my 11s chain and the cage (6800 Ultegra). The KMC chain is 5.9mm wide.
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Mick F
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Re: Chain going beside rather than round lower jockey wheel - why / how fix?

Post by Mick F »

Good idea regarding this issue.
Mick F. Cornwall
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frank9755
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Re: Chain going beside rather than round lower jockey wheel - why / how fix?

Post by frank9755 »

gxaustin wrote: 31 Jul 2021, 5:42pm Are the idler wheels Shimano 11 speed? Could you have been given the wrong ones with wider spacers?
there is a 2.2mm maximum gap between the edge of my 11s chain and the cage (6800 Ultegra). The KMC chain is 5.9mm wide.
Unless they were in the wrong box, they were the right wheels.

I rode with them today and all was fine now I've got the bottom one oriented correctly.
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Audax67
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Re: Chain going beside rather than round lower jockey wheel - why / how fix?

Post by Audax67 »

Mick F wrote: 30 Jul 2021, 10:56am I still don't see that it's even possible to run a chain alongside the bottom jockey.
Mine wasn't completely off the jockey wheel, but rather it was riding on the tops of the teeth on one side and rubbing against the cheekplate on the other - not constantly either. I should really replace the plate but it's not all that worn and it's done around 3000k since problem-free.
Have we got time for another cuppa?
roger
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Re: Chain going beside rather than round lower jockey wheel - why / how fix?

Post by roger »

Always understood that there was sideways play built into top jockey wheels, but not bottom.
Will go and try in a bit.
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