Help ... grinding chain only in small chain ring

What's it grinding on, the front derailleur cage or the big chainring? New rear wheel is probably slightly different dimensions than the old, so the cassette could be a mm or two further inboard or outboard than the old one, changing the chain line just enough to cause rubbing. I'm assuming it only occurs when in small/small?

strankov wrote:

Thanks AKH ... the front derailleur is clear and not touching the chain. The grinding only occurs using the small chainring. It occurs on every cog of the rear cassette. There is no chain rub on the fron derailleur. As I say if I'm on the small chain ring in the middle of the cassette it grinds ... and when I change onto the big ring it's absolutely fine.

New chain slightly too long perhaps, or the b-tension screw on the rear derailleur needing adjusted a touch. probably the cage sitting to close to the sprockets, which would be more noticeable on the smaller front cog I suspect.

I wouldn't say it's loud enough to call it grinding, but I do notice that on one of my bikes the big chainring is slightly noisier than the small, so the opposite of your situation. I think some chains are noisier than others too. I can only think it's some quirk of the chain and particular angles it's being asked to bend around.

I'm no expert, but if the noise is definitely not coming from contact with the chain and another component, then it must be coming form the chain itself (or the interaction of the chain and cassette, obviously they need to touch). Could you try a different chain to rule this out? Possibly re-indexing the rear derailleur for optimum quietness whilst in the small ring would be possible, at the expense of reversing the situation and causing grinding in the big ring.