Tappping has blown engine?

For a few weeks now ive been posting here about my engine tapping. I finally got it to a garage and was told that the oil was not on max and they filled it to max and the engine tapping should now go.The tapping carried on so i bought some waynies hydrolic tapping treatment i drove around 400 miles after using it with no change. I carried on driving has normal now on friday the car engine management light came on ( the gearbox?) and the stop light came on the second cylinder spark plug came out i pulled over i have tryied to screw it back in but seems to be no threads?? Before the spark plug blew out the tapping went away for around 3 hours.Is there any way to make new threads for the spark plug with out taking the head off ? Ive been told the metal bits will fall into the cylinder and break / chip the valves ?? When i start the car up the spark plug pops out hits the cover then goes back in making it tap. I was thinking to get it home i would put some wood between the plastic cover and the thing that goes ontop of the spark plug ? Has i said the tapping for months was the spark plug coming out hitting the plastic cover then going back in..

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