New chain being throw of Jockey Wheel

[jase_31]

Well summats causing it,



I wouldn't use a calculator, wrap big/big not through the mech and add a pair of links is my method.

There isn't a tight/stiff link in the new chain is there?

I based it on the original chain - but just used the calculator to check Im on the right line. New photo attacheds on small/small and large/large.

Cant see any tight links. I am not totally convinced it is not the chain. Old one is KMC, new one is Shimano (marked Shimano and Narrow - but no part number on the chain?)

 

[raleighnut]

Actually this Park Tool vid is better


View: https://youtu.be/O0YibMDWBAw


as it also shows the problems with a wrongly sized chain.

 

[Deleted member 26715]

Well summats causing it,

Agreed again, I was just curious as when I replaced the chain the other day on the friends bike, on the big/big cogs there was absolutely no slack & the derailleur arm was nearly horizontal, I left 2 extra links in & things looked far better. I was was concerned I had done it wrong.

Sorry @jase_31 for the hi-jack

 

[fossyant]

You do have a similar 'speed' chain don't you. - I.e. you've not fitted an 11 speed to an 8 speed as the width of chains are narrower. Photo's would help.

 

[jase_31]

Well summats causing it,



I wouldn't use a calculator, wrap big/big not through the mech and add a pair of links is my method.

There isn't a tight/stiff link in the new chain is there?

I will put the old chain back on (measuring as per the method you suggest) and see what happens.

 

[jase_31]

You do have a similar 'speed' chain don't you. - I.e. you've not fitted an 11 speed to an 8 speed as the width of chains are narrower. Photo's would help.

Ive examined the chain again. Some links are marked IG51, which a quick google says is " Shimano IG51 6-7-8 Speed Steel Chain".

I tempted to try another chain (i.e kmc) in case there is something odd about this. As it is off at the moment, before i buy another chain, Ill give another go clean/lube and refit again (checking measurement as per suggestions here) and see what happens.

 

[Ajax Bay]

The new chain (shimano) is being throw off the bottom jockey wheel, and runs off the wheel. I cant see that anything is bent, and have cleaned the wheel and bushing. The new chain runs OK on the cassette and front chainring.

summats causing it,

Thanks to the OP for posting photos (see edited OP).
We can see that the chain is the correct length. We can assume that the new chain is a 6/7/8sp one, correct for this Carrera Subway 1 8sp drivetrain.
I'm not sure that the symptom is being fully described. What do you mean by 'the chain being "throw[n] off the bottom jockey wheel? The chain comes in on the return from the chainring and runs directly to the guide jockey wheel. Presume you mean that the chain is bouncing around (?bumpy terrain) and the jockey doesn't collect it as normal (but not a symptom with the old chain).
Does this happen with the chain on each of the three rings? More on the small sprockets than the large ones? While riding along (assumed)? Or is this with the bike upside down or in a stand?
Finally the guide jockey wheel looks misaligned on the 'behind' image attached to the OP (but not clear how that could generate the symptom described(ish).

 

[fossyant]

Finally the guide jockey wheel looks misaligned on the 'behind' image attached to the OP (but not clear how that could generate the symptom described(ish).

This ^, the jockey wheels don't appear to follow the same plane as the cassette - could be an optical illusion, but they look twisted inwards, suggesting either a bent mech, bent mech hanger, or both. Some additional photos, a little closer to the wheel might help. The Jockey and cassette sprockets should be parallel in the vertical and horizontal

 

[Ajax Bay]

The tension and guide jockey wheels and the (cassette) sprockets should be parallel in the vertical and their axes should be parallel (horizontal)

FTFY

 

[C R]

FTFY

Geometry pedant here. As long as the axles are perpendicular to the sprockets, then the axles being parallel is enough for the planes being parallel, within tolerance of course.

 

[Ajax Bay]

Ok I'll have another go. NB @fossyant didn't mention axles, and neither did I. Sprockets haven't got axles, btw. A self-confessed pedant must take care.
The tension and guide jockey wheels and the selected sprocket should all be in the same plane, with horizontal axes.

 

[Deleted member 26715]

🍿

 

[MrGrumpy]

Just to add my rear derailleur was doing similar , chain gets caught between sprocket and plate. Not often but did when going over bumps etc. Chain length is spot on . I suspect an aligned hanger /rear derailleur issue for me. Appear to behaving itself just now but it’s had another new chain and cable replaced recently . I would the mechanics first

 

[fossyant]

Anyway, they should line up one way or another !

 

[fossyant]

With my super skills at drawing, it looks like the cassette and chain follow the orange lines, but the bottom jockey is following the red, hence when you pedal the chain will likely ride the teeth. Slight exaggeration, but the OP needs to check. An old chain will be looser at the pins so will work OK, a new chain much tighter.