With your permission I have a story to tell about another car which had an awful engine knock, and a happy ending.
On a 4 cyl FWD car w/o fuel injection I noticed that one brass screw was missing from the choke butterfly (remember those?) The noise seemed to be coming from cyl #1. I took out the spark plug and with the engine off, I poked all around the cyl with a stiff piece of wire. Then I started the engine and idles for a short period of time with the spark plug out. The screw must have been poked loose and flew out the spark plug hole. I reassembled the car and the noise was gone and stayed that way for at least the next 40K miles. I was very lucky!
