What can I do to stop my front dérailleur rubbing against the crank arm? I recently changed the crankset of my Cannondale Synapse 5 from the stock FSA Gosssamer crankset to a Rotor 3D24 crankset with power2max power meter. This was a bit of an iffy modification to make - the Cannondale frame has a BB30A bottom bracket with a 73mm shell width for 30mm spindles. However, the Rotor cranks are 24mm. I took the bike to my LBS and we eventually got everything to mount using some Wheels Manufacturing shims (BB30-UNIV).

However, there is a problem now - the front derailleur now rubs against the crank arm as the crank passes over the derailleur, causing a very annoying clicking noise. I can stop the rubbing by tightening the high limit screw in all the way, but now the derailleur itself rubs against the chain, and doesn't have that 1-2mm clearance that is recommended.

I have a bunch of spacers that came with the Wheels Manufacturing shims, and I've taken the crank off and installed some on the drive side. This has the effect of pushing both the crank arm and the chainrings out - so the clearance between the chainring and the crank arm is still constant and small.

Is using these spacers the right thing to be doing? I'm wondering if this is a chain line issue?

I am also considering getting http://kogelbearings.mysimplestore.com/products/cannondale-bb30a-24-for-rotor-cranks but I don't really see how that will solve my problem - it seems to be the distance between the crank arm and the chainring itself...
If you already adjusted the front derailleur, there is not much to do. As you wrote yourself, the distance between crank arm and chainring is too small for your derailleur. Ask Rotor about compatible derailleurs.

The main reason to have derailleur not touch is not noise. The derailleur scratches the crank, which creates a starting point for cracks.