onan 7000 watt marquis

Found it! At least for our old BFA "4.0 RV Genset" which was twin-cylinder opposed 1800-RPM. Parts list shows Flywheel with four holes around the crankshaft hole. A Steering Wheel or Vibration Damper Puller (with the correct capscrews to thread into the flywheel) should pull it. You'd back the bolt holding flywheel to crankshaft out a couple turns and let the puller bear on it. At least that's how the pic in my manual looks. Of course the design could have changed. BFA was an old machine.

NOTE: OP seems to indicate that the flywheel is between Engine and Generator sections. The gensets in my manual have the flywheel in a blower housing at one end of the unit, not between the sections...