Originally Posted by mcoomer
I put a new Dura Ace crank on my SL2 when I built it and I can't believe how much noise the chain makes on the chainrings. When the chain line is near perfectly straight for the ring I'm on it is very quiet but if I shift up or down more than a cog or two in the back I can really hear the chain on the rings. I've got just over a hundred miles on the bike and just gave the front der a tweak because it had shifted some but otherwise my drivetrain alignment appears good. I'm running a SRAM 1090R chain but if this continues I think I'll pick up the Shimano CN-7801 and see if that's more quiet.
So, is there a break in period for cranks? I'm wondering if there isn't just a bit of an edge to the chainring teeth that will be smoothed down. Let me know what you think.
Lots of things in play here ...
First, bike frames keep getting lighter and lighter and, as a result, transmit more noise. Think of a nice violin and then think about how much quieter it would be if all the wood in it were an inch thick. One of the noisiest bikes I have heard lately is the Specialized Transition TT bike. That's a pretty exotic frame and it makes a LOT of noise with very fine DA components.
I'd be surprised if the change of chain does not help a little. There's a reason that people will pay $80 for a nice Campy chain. It just makes the whole drive train smoother (and, quieter). SRAM chains are great, but not specifically designed as part of a Shimano gruppo.
Cranks, of all of a gruppo's components, probably will affect how much noise gets transmitted into the frame (= loudspeaker, for purposes of this discussion). And, again, the lighter the crank, the more noise it's going to transmit (again, consider the violin analogy).
So, concluding, there is significant correlation between the amount of noise a bike makes and how "high end" the frame and components are. You want a really quiet bike? Go for a heavy steel frame 10 speed and lube everything with SynLube.
To answer your specific question about "crank break in" ... It's probably as good as it will ever get after just a few miles (to wear down any sharp edges) and then it just goes down hill from there.