I have a couple questions on what brought me here: I have a 98 4 dr sport 4.0 in6 and its knocking bad. My "mech" said he re-tighten the flex bolts and some of the knock went away but its back, so if the bolts loosen wouldn't they fall out? What is causing the knock or tick?. Can you see the center of the flexplate to check for cracks without lowering the tranny. There is growl with the knock and sounds like "S*&$" just being knocked around toward the rear and lower pass side of the eng. I have been told its a rod knock on the crank, or piston skirt broke, told to drop pan check for debris and then hand inspect the rods. All should be tight, if not then that's the problem. Could I get away with installing a oversize bearing installed to tighten the rod up? How long will that last? This is my daily driver and second engine that was pulled from a wrecker with 90k. I also have limited funds and need to get fixed before it goes Poof! My Mech wants me to pay 700 for rebuilt kit or 1k for rebuilt short block.

 

https://www.cherokeeforum.com/f51/ho...ocking-125547/

If you read this write-up, a threadlocker was used to help prevent the bolts from coming loose. Did your mechanic use anything like that? Or just put the bolts back in as is? I'd dig in there and tighten the flexplate again before paying your mechanic a grand to rebuild your engine (especially if you aren't sure the engine is what's making the noise).

And to answer your question, the bolts wouldn't necessarily just fall out. They could just become loose and cause some noise

 

X2 on Sport there^. Of course if they are loose that's no good. It they were loose enough to tighten and it helped...fantastic! Might be that 4.0 is fine.

I've had engines with a rod bad enough that if I held the throttle, (or shimmed it), up to say 2500 rpm , I could pull a plug wire at the dizy and have it go away. Or at least tell me which cylinder it was. Then sounds get pretty "funny". How many miles? Gauge or light? Light flicker at hot idle?

Cold start it does what? Hot pulling up a hill ... what? I might even park it hot after a good run, nose up a bit. And drain the oil like that. Cheez, I suppose if a guy could, hot there on a slope with the front 6 or 8 inches higher slosh it forward and back a bit before draining it. If you have a broken skirt maybe you will find something in drained oil to add a clue.

 

Thanks everyone for the quick reply. He's a good ole boy who works on monster trucks for a living and him and his brother in law are always working on engines so I assumed when i brought it back the second time and he said he will use some loctite on them, I took his word. I feel funny questioning a guy who knows more then I do in this field. He did say that 2 were loose but mentioned if the flexplate was inspected. They think its a rod maybe 5 0r 6.
listen:

 

Doesn't sound like rod noise to me. Sounds like a flexplate bolt, torque converter bolt or some other external item.
Can you narrow the location down with a mechanic's stethoscope? Or even a length of tubing?

 

9.9----9.8----9.9------10!. Nice Job on the video. (the 10 is from me).

Mikes, and the way sound get's picked up sure get wired. Sounds "present", right on-top. I might have heard something similar when pushrods were hammering away on the bottom of the valve cover. You might simply feel that with your hand. Idk though sounds loud below also. (if a bent rod comes off the rocker, the lifter can "fire" it up)

Besides taking another good look at those flexplate bolts, (you do know they are right there under the inspection plate), I'd pull the plugs and see what they look like. If you find a bad looking one you might feel for compression there with your finger. If you have a piston that's fallen apart that should be pretty clear.



Besides what Radi mentioned, another trick is to use a section of dowel, (couple feet of broom handle). and press it on a spot and put your ear on the other end. (being careful of course around moving parts).

If that IS a piston, running it will ruin the block, if it hasn't already. Of course a compression test would be a good idea....

I wonder what it sounds like if a valve keeper lets go? That might knock more going slower, but less when the valve didn't have time to drop.