Ok.

I just did mine today and everything went fine. This is what I did:

1. Balanced the Fan (FIRST !!!)
2. Finger tightened the adaptor.
3. Took a 12mm socket w/wrench and at the same time held the fan assembly from the stem, while tightening with the socket wrench. (Need some good finger excercises before doing it this way). This way you are not holding on to fins, nor are you puting torque on the recoil starter.

If your fingers are long and thin you can probably hold the stem from the engine side, which would make it easier. Mine are too big to fit on the engine side.

If you think the fan was tough, wait until you install the pipe into the duct

BIG HINT HERE: Don't glue the tail and elevators until you complete the engine install, including the pipe. This way you have more room to reach in with your hand from the rear duct. You will need it !

Good Luck