Sure sounds like a heavy knock. The kind that would come from a loose rod. I hate to say this but it looks like you had better dive under the truck & pull the pan off and see if you can locate the offending rod.
I do feel for you. I had to pull mine down four or five times 'till it was right.

 

I pulled the oil pan, since it seems to be where the noise was coming from. I pulled all the caps and began to mic them, to see if any of them are worn. I found one cap that measured way out! The bearing still slides in, but there is a space between the bearing and the cap! I suspect that this is my problem. All other bearings look great. I did have one question. I have no side to side, or up and down movement on my bearings, but I can wiggle them slightly from front to back. Is this normal? I know I need to replace the worn out rod, but I want to make sure I don't need to re-pull the engine and change all the rods. It is pretty obvious where my noise was coming from, but I want to be sure.

 

Is this a main or rod bearing that has the gap? Definitely not good!

Front to rear movement (clearance between rods on a journal) is OK, I think the specs are something like .015". It's very hard to distinguish the rod sliding on the journal from rocking, which is bad, with the piston/rod installed.

 

AAAAANNNNNDDDD!!! I'm a dumba$$!!! I put a new rods in this morning, and turned the engine by hand to make sure everything was clear. I put the oil pickup tube on, and cut my finger...it was only then that I realized the noise I had been hearing was the crank hitting the tube...I'm a failure as a mechanic!! At least I have solved the mystery! When I put the crank in the first time, I spun it to be sure everything was clear, and assumed the oil tube would be fine. I never checked it after the tube was on. There is a groove worn in the oil tube, and it almost punched through! I have welded the tube, and bent it about 1/2 inch down, and the crank spins fine! This is what happens when you cut corners, and dont check everything twice!

 

LOL, so maybe you found a bad rod just before THAT became a problem?!

Make sure you have the correct tube and oil pan combination. Do you have a truck pan? Using a truck pan with a car pickup, the screen bottoms on the pan and bends the tube up as you tighten the pan bolts. (Maybe it's vice versa, car pan and truck tube, I forget).

 

It looks like I kept myself from just having to do this again in a few months...now at least I know what it was, and I have new rods...the wife is going to kill me if she finds out I spend all that money for nothing...Im just going to tell her it was the flux capacitor...

 

Bad rack and pinion molecules, honey. I sure did save us some time and money! If those had been left to go bad, the muffler bearing could have spun. That would have doomed all of mankind!
Mum's the word.

 

I had that sinking feeling on my son's 302....the dipstick was twanged so that the end was being hit by the crankshaft cheek every time it came around. It made a terrible noise that I was sure was a rod bearing. Fortunately for us, the red-neck stethoscope worked & I pulled the dipstick to cure that rod knock.

On the bright side, at least you know what you have now with the new rods.

Dan

 

Alan Jackson said it best....

 

You guys are too funny! Unfortunately she knows when I am full of it...and I am sure she would see through it. I just keep telling her to hold all her complaints until it is done and we are cruising on a Friday night...I think she will change her tune!