all your feeling when the motor is intact, is the piston hitting the taper point of the sleeve(compression) which is right on the mark. and yes with it apart, when the motor has good pich it will lift the sleeve out when you rotate the flywheel.....
also are you using the right PLUG for the motor???????
just making sure you really arent hitting something on the top side...(any marks or dings on top of the piston?)