RD lower pulley wobbles up/down in low chainring
07-23-22, 02:11 AM
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RD lower pulley/cage wobbles up/down in low chainring
I replaced my FSA 50/34t with a Sugino replica 42/26t cranks with SPA chainrings.
I can see the lower pulley/the cage of my RD goes 2-3 mm up/down together with cranks when in the low-low (the cage is almost parallel to the ground). The wobbling of the cage persists across all the cogs but becomes almost indistinguishable at the high cog. No issues when on large chainring.
Is my lower chainring asymmetrical and needs to be replaced? Any other causes? Shall I ignore it or do I take it back to the seller?
I can see the lower pulley/the cage of my RD goes 2-3 mm up/down together with cranks when in the low-low (the cage is almost parallel to the ground). The wobbling of the cage persists across all the cogs but becomes almost indistinguishable at the high cog. No issues when on large chainring.
Is my lower chainring asymmetrical and needs to be replaced? Any other causes? Shall I ignore it or do I take it back to the seller?
07-23-22, 06:33 AM
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Is this a new chain? If it's the old chain, how many links did you remove? What's the position of the derailleur cage relative to the ground in large-large?
Is the chainline of the new crankset identical to the old?
Is the chainline of the new crankset identical to the old?
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07-23-22, 06:44 AM
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Back in the Bio Pace chain ring era the industry found that the slight rotational movement of the rear cage (as the chain slack was taken in and played out) made no appreciable difference to the life of the parts. I suspect your ring is not really round WRT the BB axle. But the crank arm bolt holes also might be where the tolerance is off too. Andy
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07-23-22, 09:38 AM
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No part is perfectly concentric, nor is any assembly. I would consider 2-3 mm of derailleur movement irrelevant; the amount of non-concentricity of the chainring is certainly less than this. You could see if loosening/moving/re-tightening the chainring helps but I would not bother. And I am pretty fussy about this stuff. The only thing to check is to ensure that the movement is not because of excess play/looseness.
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07-23-22, 09:54 AM
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- Same old chain, absolutely no wear according to the tool
- Removed 4 links
- Chainline should be either the same or +0.5mm, hard to tell
