[Henry Schmidt]

Over the years we have seen engines that fit the symptoms you describe. They are generally engines that have been shipped or dropped.
What might be happening is carbon in the cylinder. It is common for carbon to form on the the chamber and when the engine is jarred the carbon come loose from the head and falls into the cylinder and when the piston moves up the carbon bits are compression and the engine stops. If you can turn the engine upside down you might free the carbon bits.