what is this bit of my bike and should it be all bent and twisted?

[darkling]

Okay so I'll look at my mannual later and it might give me some clue but I was looking in that little window that shows you the smaller sprocket that the chain goes on. (trying to diagnose wierd clunking sound when riding)
In this window I can see the front sprocket. It's held on by this big bolt thingy and underneath that seems to be a washer type part. Its this bit I am concerned about cos its all bent inwards and warped and like..bits of this washer bit are bent over itself.
Whats that thing? Is it a washer? Why would it be bent like that? Would that explain the sound?
this new sound only started after the mechanic put a new chain and sprockets on. This sound isn't normal for my bike but it is my first o ring chain. i think.

 

[Dani G]

IWhat the first answerer said: it's a lock washer.

As for the noise: an o-ring chain is not noisier than a regular chain, but it is wider. If the clearance is really tight, it migh rubbing against the sprocket guard.

It is also possible, though not very likely, that the chain is not to the exact proper dimension for your bike so it is a little loose around the sprocket teeth.