I have a 2001 dakota with 140000 miles on it. I have picked up a knocking noise when the RPM is around the 3500 range. Thought it might be a timing chain so I replaced the chains, gears, guides, and tensioners. Changed oil with 5w-30. The motor is very clean inside. The noise has increased. It is quiet at idle and under power, but really knocks when just maintaining speed (floating the throttle). Sound is from the right side rear and can be heard better under the truck. The stehescope picks up the sound on the transition between the bellhousing and the back of the block. The torque converter bolts are tight and I do not see any cracks in the flexplate. The motor runs extremely smooth and does not make any noise accelerating or decelerating. It only knocks when maintaining speed. Any ideas? Rod bearing?

This engine idles smooth and quiet. The oil pressure is always in the upper range more toward the 3/4 mark. If I rev the motor, I can hear the knock briefly as the RPM drop off, and then return quietly to idle. This is still one of the smoothest running engines I have ever owned. Just ordered rod and main bearings. I talked to a local engine rebuilder who told me that he has seen alot of 4.7 motors with bad rod bearings. He recommended pulling the pan and checking the rods. He said as long as the knock isn't there all the time and the crankshaft journal isn't scored, I should try new bearings.

 

Although the OP never came back to the thread, I'll bet he dropped a valve seat!!!

I'm going through it right now on the 4.7 HO in my Grand Cherokee (102K miles). I'm finding out it's VERY common as the hardened steel seat is pressed into the aluminum head. Over time and with heat, the aluminum expands and the steel does not, so the seat drops right out.

I had the same symptoms but with cylinder #2. If the cylinder wall in the block checks out ok, you can get by with a re-manned head (about $500) and a piston (about $90) which is WAY cheaper than an engine replacement. But the labor is gonna suck *****. OHC engines take about 8 hours to pull the head vs. about 2 hours on a traditional pushrod...

 

I am having the same problem I popped the valve cover off and here is what it sounds like. Rocker arms are very loose and the sound is very loud when the truck is running.

It is very hard to start also.

http://youtu.be/E11diY1LUuY

 

Seriously?! How 'bout broken/bent connecting rods or a rod through the side of the block? A blown head gasket is a walk in the park in comparison.

 

Dropping the oil pan to replace bearings is a band aid. Not a long term resolution