I am running a 170 mm DA crank (7400 I think) with DA 7 speed drive train. I would like to switch to 172.5 cranks. What type of issues will I face if I run a diffrent crank set? What chain issues might pop up? Or, am I fine running any DA crank and keep with a seven speed chain?
Unless it's the exact model crank, there's a possibility you'll need to replace the bottom bracket because 1) it may use a different spindle type (square taper, splined, external/integrated) or spindle length. BB sizes: http://sheldonbrown.com/bbsize.html
The bottom bracket type must match and the length should match (for optimal chain line) the crank, but the chainrings won't care too much about the chain that is used on them.