Just had new chain and cassetee fitted

[User16625]

to my MTB. Now I find when on the small chain ring the chain wraps itself around it and jams against the front derailer. Whats the likely cause of this and how can I resolve it?

 

[RecordAceFromNew]

Sounds like you have one ring suck. If I were you I would look for shark tooth profile on that ring, and check chain length is correct.

 

[User16625]

It was fitted by a professional so I would assume chain length and type was correct. However I will try to look into that. I am led to believe the front sprocket maybe worn based on that info. I had the chain and cassette changed on my road bike without having this problem so I hoped the same could have happened with my MTB. The sprockets dont look particularly worn. I hope its a worn chainring coz I will be seriously pissed if its due to incompatible parts or setup. I pay pros specifically to avoid these problems.

 

[accountantpete]

Could just be muck - give the small ring a wipe and then oil it and see if that cures the problem.

Otherwise - new ring.