Right about using rope.If you keep the piston above the exhaust port near the top with rope in the cylinder this will never happen. How could it with all the ports covered? Rotating the crank because you have it locked in the wrong direction is how this happens. Pull the rope and set the piston properly.
Been doing it this way for 15 years with the same piece of rope and have yet to jam up a cylinder. I have knots tied in my rope so I don't have pack so much in.