Take out the spark plugs and put a bit of oil into the cylinders.Let it sit for a couple of hours and then try turning the engine over at the crankshaft pulley with a breaker bar,working it back and forth.If the engine turns freely,it could be the flywheel has a bad spot on the ring gear and the bendix isn't meshing with it.Also,make sure your starter isn't a defect.Take it out,ground it,hit it with some juice and see if the gear spins and moves toward the head of the starter.
