fruitloop:
a lot of engineers look for a positive turning of N1
This bit may not apply to either CFM or V2500, but is a bit of history from earlier high-bypass engines: A new engine, or one with a fresh LPT module, may have too-tight clearances, and the N1 rotor may not turn freely - it may not even turn at ground idle.
The solution applied was to shut down after perhaps 30 seconds, wait a bit for the LPT case to expand from the heat, then re-start. By then the blade-to-shroud clearance should be opened up a bit (the rotor discs are massive and don't heat up as fast).
Your mileage may vary!
