Ok, so I purchased my 80 series back from the guy I sold it to 2 years ago. He only put 20k on it, but I went to pick it up yesterday and on the way home it started to get hot. I stopped and turned on the heat, immediately the temp went down, however it started to knock pretty loud. It sounded to me as if it were on top of the engine, but a friend says it sounds like it was coming from the bottom. We took it to his shop and performed a compression test, Cyl #1 had 120psi, #2 150psi #3 130psi #4 150psi #5 110psi #6 150psi so I guess that was good, we removed the valve cover and all appeared well in that realm, we turned it over with the spark plugs removed and no sound. We replaced the plugs w/o wires, still no noise... We were thinking rod bearing, but we are second guessing now, anyone else with any good options????