The flywheel is located inside the tractor and the clutch that you use to change gears rides on it. Is that the flywheel you are talking about?
Flywheels tend to be solidly attached to whatever shaft they are on and it probably shouldn't be loose but I'm not sure if you are talking about the flywheel or the clutch disc or what exactly. :confused3:
Here's an online operator's manual for your tractor if you don't already have one.
Operator's Manual - International Cub-154 Lo-Boy
You might get a better response to your question if you posted it in the "Cub Cadet Tractors" section http://www.tractorbynet.com/forums/cub-cadet-tractors/