Before you go pulling the motor, you might want to wash it real good pull the valve cover
Off and inspect the head and valve train for cracks , rocker arms and valve springs.
If you think your just going to do a engine swap, might check with some of the shops
That do Hemi swaps. They will usually have a couple low milage stock engines that
Got pulled .ie.3.8's 3.6's. Trail jeeps in Golden, Rokmen in Littleton . Just a couple...
I don't know any shops in Colo springs....

 

Maybe it's my crapy speakers but it sounds like exhaust manifold to me , not a knock ?

 

As someone previous mentioned, the noise just might be from the valve train. A method I've used on other engines is to take the valve covers off and visually inspect while having a buddy turn the engine over with a breaker bar. If nothing turns up on the first visual inspection, I've run other engines with the valve covers off (which is a bit messy) to look for valve train related problems.

Best of luck with it,

 

Spun main bearing...

https://www.jk-forum.com/forums/stoc...3/#post3953504

 

I found a video online on how to test for a bad rod bearing. Seems to be simple test by just taking the spark plug out, putting a straw on top of the piston, turn it to top dead center, then start it on the downward stroke. Then use a screwdriver and push down on the piston head (I don't like the idea of using a screw driver so I will use a dowel rod) and see if the piston moves. Obviously it should not move.

Thanks for the other ideas. I will need to go through those as well if it is a rod bearing.

Regardless of what it is, I need to get the quads out of the garage and get the Jeep in the garage to start working on it.

If I do need to pull the engine, any gotchas? I pulled and replaced a 4.0 out of an 88 Cherokee a few years back and had no issues. I am very mechanical and can teach myself with books and videos. I have also searched here and youtube and I have not found a video of someone pulling the motor with detailed steps. Does one exist? I am thinking I will record my process and post it.

 

That's a rod. Pull the pan and take the caps off one at a time to inspect the crank. As long as there is no damage to the crank you can get away with rod bearings, no need to pull the motor. You can clean the crank with some Emory cloth if necessary, sometimes there's a little build up of the bearings on the journals. You should also check your PCV system, a sticking PCV valve will suck the oil right out of the crankcase and the first thing to go is usually the rod bearings. I've put rod bearings in about a dozen 3.8's and have had no issues. Good luck.

 

D-Rick thanks for the reply.

What am I looking for when inspecting the crank? I am guessing scoring from a bad bearing. How would I determine if the crank is salvageable or not?

Will it be obvious if the PCV valve is stuck when inspecting it?

Any tricks/gotchas when replacing rod bearings while the motor is still in the Jeep?

Thanks for you help.

 

Since the Jeep died and I had it towed home all I have done is record the video of the sound the engine is making. Otherwise it has just been sitting. Today I noticed a puddle of oil under the Jeep. It is leaking from the bell housing. Now I am thinking the rear main is shot as well.

 

Pulled the pan today.

That is not even all of it!!!

 

That's not good. That looks like more than bearing material... Might be time to consider an engine swap unfortunately.