If the electrode is smashed on the plug, something hit it. I have a feeling a valve is bent. Honestly, before putting any time or money into the engine, I would pull the head to see what has happened. If number 1 is damaged, chances are others are too. You may be better off replacing the engine with a good used one.
Let me know if I can help.
Joe
Tuesday, July 21st, 2020 AT 10:13 PM