I know this will most likely NOT be the problem with your truck, but I have to pass on this tale . I changed the front motor mount on my 261 last week. To lift the engine I put a 2x8 across the bottom of the oil pan (figuring that would distribute the weight to the sides of the pan and it did) and jacked it up. Changed the mount, no problem, dropped the jack and board. Then I noticed that I left the cover plate off. No biggie; jack the engine back up but this time I grabbed a smaller board that didn't quite reach to the oil pan edges. Replace the cover, drop the jack and start engine. I would have sworn that I broke a rod or pin or something. My knock was steady though and increased with RPM. It truly was a puzzle to me until I climbed under the truck to listen. OIL PAN NOISE! I put my hand on the pan and I could feel the knock. I had dented the pan just a hair. I took my hammer and smacked each side of the pan which popped the dent out and the noise was gone. These trucks are so easy to work on! (sometimes). Good Luck.
