I need advice on what could cause a loud engine knock in my motor. Here's the story in a shortened version. My 1996 Mustang GT 4.6 liter sohc v8 , 5 speed manual transmission, blew a head gasket,. (among many other problems before that.) So, I got a used motor from a 1998 Mustang GT 4.6 liter sohc v8, automatic transmission. I got the 1998 motor for $500, and was told it had about 78,000 miles on it. So, my friend Jason finished the engine swap day before yesterday and even though the car fired right up, it had a loud knock. So he shut it right off. He told me he tried everything to get it to stop, including "honey oil" whatever that is, but it still knocks. What could cause this? Could he have damaged the motor during the swap? Any ideas? I'm about to give up on this car, I've owned it for over three years now and it's been parked almost the entire time. I can't find a good mechanic and was scammed when I got the car. Anyway thanks for any tips.