I marked up your picture to show the flywheel and the rope sheave (what you called the aluminum lid). The sheave is what you wrap the starter rope around to start the motor. What has been suggested to free up your motor is to wrap a strap wrench around the perimeter of the flywheel and see if you can rotate the flywheel to free up the stuck pistons.
You don’t need to remove the flywheel or the rope sheave before you get the motor freed up. If you want to remove the rope sheave off the top of the flywheeel you would just remove the 3 slot head screws. The flywheel is removed by removing the center nut. But again, you should get the motor freed up first before removing the sheave or flywheel. You need to leave the flywheel on to get the motor unstuck first.
Yes, do what Bob says! If you rock the flywheel back and forth with the nut loose you will ruin the flywheel keyway! Don’t ask me how I know this. Some people just gotta learn things the hard way!
dale
