Chain not sitting properly on chainring

[briggsaj]

Hello all,
When shifting down to the middle ring on the front, the chain wasn't going in to the groves of the chainring and sometimes span on the teeth. I recently replaced the chain and the middle chain ring, which seemed to solve the problem, but it has started again - taking a few revolutions for the chain to sit properly on the chain ring.
Not sure what to do next. Could the chain be too long? Any pointers appreciated!
Thanks

 

[woohoo]

Make sure that the chainrings are aligned properly; they have index marks that should line up. I sorted a similar problem on a mate's bike and he had misaligned the middle ring (by 90 degrees) when he had re-assembled the chainset.

 

[fossyant]

Also check that the front mech is pushing the chain far enough - may take a little adjustment at the shifter adjustment 'knob'.....

 

[spandex]

Is the ring the right way round?

 

[briggsaj]

Thanks for the replies so far - I'm a bit of a novice at this - how to I check it is the right way round and also aligned? (are the index marks easy to spot?)

Thanks again!

 

[PpPete]

If it's a current Shimano chainset then detailed instructions about which way round the rings go and lining them up are all on http://techdocs.shimano.com/techdocs/index.jsp