New Chain on 12 speed shimano - thrumming?!...

[edruid]

Swapped out at just over 50% wear.

Shifting worked fine.

But now there is a constant thrum, no matter how I adjust the tensioner

And the chain now keeps slipping off the front ring (not great when you're in Snowdonia).

Lubed the new chain before use.

Definitely same link count

Not had this before, anyone got any theories?

Thanks

edruid

 

[theremotejuggernaut]

Have you routed it around the rear mech correctly? There's a little tab between the pulleys, the chain has to be on the correct side otherwise it rubs.

Have you got the chain the right way around? Writing on the outside?

 

[irie]

Have you routed it around the rear mech correctly? There's a little tab between the pulleys, the chain has to be on the correct side otherwise it rubs.

Have done that myself.

 

[theremotejuggernaut]

Have done that myself.

Me too. And the chain being the wrong way round. And I still do both, despite knowing not to

 

[edruid]

Have you routed it around the rear mech correctly? There's a little tab between the pulleys, the chain has to be on the correct side otherwise it rubs.

Have you got the chain the right way around? Writing on the outside?

Thanks, would love it to be either of those easily correctable mistakes (which I have made before) but sadly not this time . . .

 

[theremotejuggernaut]

Does the chain mesh properly with the chainring? Could be a worn chainring being unhappy with a new chain?

 

[edruid]

Does the chain mesh properly with the chainring? Could be a worn chainring being unhappy with a new chain?

Is what i fear (££). How can i tell?

 

[theremotejuggernaut]

If it meshes properly, there will be no gaps between the chain and the chainring. The links will fit perfectly between the teeth (also, narrow/wide links need to be aligned with the narrow/wide teeth).

I'd flip the bike over and pedal it slowly looking at the chainring, if it looks like the chain is climbing out of the gaps between the teeth then the chainring is worn.

Also, if the chainring is worn, it can sometimes hold onto the chain as the chain moves around the bottom of the chainring. Look at the bottom of the ring where the chain starts heading back towards the derailleur. The chain should slide cleanly off the chainring. If it looks like the chainring is dragging the chain around, then it's another sign that it's worn.

Same applies to the cassette. The chain should sit nicely between the teeth.