So $100 later, I have my broken intake manifold back. Seems like the furnace weld technique was the answer. All bolted back up and finally fired up last night.
After a few minutes the motor develops a very LOUD ticking/knocking sound from the top of the motor. All looks to be in order, no exhaust leak evident. Engine seems to run strong, temperature is normal.
After my wife talks me down from the roof...... I pull the fan belt. The noise immediately goes away, engine sounds great. Spinning the fan and generator by hand reveals no rough spots, play or unusual resistance to free spinning.
I replace the fan belt, start it up and the motor is knocking again. LOUD. Fan blade is not striking anything. Could it be the water pump impeller? No leaking visible. Ugh........ Check out my video clip. -Steve
https://youtu.be/LEN59OvK2XM