Turn the flywheel, you should feel resitance when you get close to top dead center. You could also disassemble the engine. Try to push the piston through the sleave (light presure). if the piston goes up thru the sleave the engine is toast. Finally get a compression gauge. Your engine should have about 30 lb of compression. If it is down to about 20 lb your engine is toast. When you install the compression gauge on the engine pull the pull start about 5 or 6 times.