Remove bar and chain. Remove pull start cover. Remove spark plug. You should be able to turn/spin the flywheel over by hand with almost no resistance. It should feel smooth to the touch as it's rotated with no hang ups or grinding.
If ya hear/feel a noise or grinding, check clutch for a broken or worn out spring that is dragging on the spur drum. If that all is good, remove the muffler and use flashlight to inspect the piston through the port. Should look smooth with a bit of black carbon on it. If ya see any "scoring" or damage like vertical scratches or chunks missing, will have to tear apart engine for further diagnoses.
Also, the crank bearings on these little guys have a plastic cage that hold the ball bearings apart. I have seen these cages fail and lock up a crank or make it difficult to turn.
