Chain rubbing rear derailluer - Help!!

wattbe

Hi, I recently transferred an 11 speed XTR groupset from a full sus to a new hard tail. It's all set up correctly - b tension, limit screws, indexing etc but no matter what I do, the chain oscillates and starts to rub against the little plate in between the two jockey wheels. Its the XTR M9000 mid cage rear mech with a Hope 34T narrow/wide ring up front. The chainline is about 50mm. The chain is the correct side of the plate and it only happens when pedalling in the smaller cogs and only at higher RPM's. I can reproduce it in the work stand. Took it to a good mechanic and we changed front chain ring, replaced rear mech with a new one, new chain, replaced the drop outs/ mech hanger with a new one and it continues to make the noise.
The groupset is new (150 miles on it from previous bike) and checked the cassette has no worn teeth. Cassette taken off hub and re-installed but still the chain vibrates on that little plate - it's actually worn two grooves in it.

I'm at a bit of a loss. Spoken to Shimano and they have never heard of this problem. Any help/advice would be massively appreciated.

The Rookie

Are you saying it rubs on that little section that bends across between the two plates (the one people often route the chain the wrong side of) or against the inside of the main side plates?

If it's the former it may have just been bent in a fraction, so I'd try tweaking it out a bit, if it's the latter it sounds like a jockey wheel problem.

wattbe

Yes it's the little plate in between the two jockey wheels (the one the chain can be routed the wrong side of)
The only thing I can do to stop it happening is to increase the b tension so that there's a 10mm gap between top jockey wheel and largest cog. Then if I change into the smallest sprocket the chain doesn't rub the tab at any rpm. But then I'm stuck with incorrect b tension which reduces shifting efficiency. It's very odd..

The Rookie

It is odd, have you checked the chain length is correct.

Is that clutch on or off, I would have thought that with the clutch damper working it would prevent that?

Worth seeing if that tab has been bent in further than it should, what is the static clearance?

Dirtydog11

Does sound like the chain is too long if it only rubs in the smallest sprocket. B knuckle would also suggest it's related to tension, bit weird though.

wattbe

Yeah - tried different chain lengths, big to big plus two links then made shorter by two links, this fixed it but then I can't get any where near the correct b tension, closest I can get the top jockey wheel to biggest cog is 11 mm instead of the recommended 5-6mm. I then made the chain too long but this made it worse.
When I have the correct chain length the only way to stop it happening again is to wind the b tension out to 10mm, any less and the chain rub happens. Clutch on or off makes no difference. I'm starting to think that maybe some chain rub on that plate is normal at certain rpm's in certain gears as I've just seen my brothers rear mech and he's got s wear mark on his too (standard Deore mech). Just never noticed it before. Anyone else noticed this?

The Rookie

I'm not sure you are sizing the chain right take some links out the right size and the mech should have been pulled into the cassette.