Hey, guys. Still trying to figure out what's making the annoying knocking sound in my little 2.5. Been searching high and low on Google and Youtube, but can't find anything that closely enough matches what mine sounds like. Here's a quick rundown of what I hear....

First, it doesn't start knocking as soon as you start it when it's cold. It takes a little while before it'll gradually start as it warms up. There's sometimes a fast rattle as soon as the engine catches and fires, but only sometimes. Doesn't do it every start and only for MAYBE a second.

Also, you can only hear it at idle, or just slightly off idle. Seems over 1K RPM, it either goes away or gets drowned out by the engine. It also seems to be coming from either the top or middle area of the driver side of the engine, or the oil pan. I can't quite pinpoint it accurately....

Oil pressure seems good according to the dash gauge. I do have a mech. gauge still plumbed in from the PO and both read right about the same. I've got upwards of 40-60 psi on cold start and driving, and usually a bit under the 20 mark at idle, probably closer to 10-15.

I get asked a LOT if I have a diesel....As much as I actually want, I don't. Lol I got told by someone who works on Jeeps quite a bit that it could be the timing chain. What do you guys think of that? I'm still leaning more toward a rod bearing, or possibly even cracked exhaust manifold since the knock pretty much goes away with the #4 cylinder disabled (unplugged injector).

I know I've asked about this a lot, but it's driving me nuts and I'm having a really hard time finding something definitive. I WILL be going out in the morning to try and get a video clip where you can clearly hear it.

Appreciate any and all help, guys! I wanna keep this baby running as long as I possibly can so I can hand the keys to my first born someday....

 

You may find this useful:
http://remanufactured.com/Engine_Diagnosis_101.htm

 

I appreciate the link, but maybe I'm just too dumb or tired to make enough sense of it....Lol I'll check it out again in the morning after I try and get a good video. I'll make sure to have one part all cylinders firing, and then disable them one at a time so you can clearly hear the difference.

 

My guess is always piston skirt, although the fact that it goes away at higher RPMs seems to indicate otherwise. Probing the block with a mechanic's stethoscope might be telling. Of course, probing the oil pan might be even more telling.

 

What WOULD a busted skirt do? Wouldn't the noise be louder as the engine revs up and vice versa? Same with rod bearing? I'll check the rod bearings tomorrow while I've got some downtime. Gotta replace the pan gasket anyway, so....Lol

 

This:

 

Okay, so here's a bit of an update for y'all. Got underneath with one of those stethoscopes and the knocking sound is most pronounced in the pan, seemingly more toward the middle. Going off that, went and got a gallon of oil and a pan gasket and went to town removing the pan.

Got it off and out, felt the rod caps and all 4 have some play front to back, maybe about 1/16th of an inch? VERY LITTLE, if any side to side movement, though. One other thing I noticed is two of the caps are stamped with the piston number, but what's odd is number 1 is stamped twice with "#1" while 4 is only stamped once with "#4". Numbers 2 and 3 caps are clean, no stamps on them. Does that mean someone had this engine apart before?

Also one other thing was the bolt that holds the oil pickup to (I'm guessing it's the....) oil pump assembly was OUT of the hole completely and laying in the bottom of the pan! I reinstalled it and torqued to 10 ft lbs, even though I couldn't find any specs on it. I just went to 10 so I didn't strip it and I figured that should be enough to hold it in place.

So, after all this, what do you guys think? Bad rod bearings, or maybe that bolt was rattling around somewhere? If it helps, the knocking virtually goes away completely with cylinder 4 injector unplugged. Runs like crap, but hardly no knocking sound.

 

Sounds like it may be a piston failure in cylinder 4.

 

Got me lost, cruiser....lol piston failure?

 

Broken piston skirt. Piston rattles in the bore when there's combustion, but is quiet when there's not....

 

Ah, okay....That makes sense to me. Of course, me being me, I didn't look for visible damage to the pistons while the pan was off. Just checked the bearings out....*facepalm* So, if it's that after all, will that constitute a full rebuild? If so, I don't think I could afford that and I'd have to pull an engine from the JY eventually....

 

Need to verify it of course. Oughta be looking for a good used engine.

 

Thanks for the help, Cruiser! I'll start shopping around for a good used long block.....What would you consider a fair price for one? Local JY would charge $169.99 for a block and head, but without ANYTHING else on it, plus a $50 core charge. Problem is, I was only able to find two 2.5's within a 50 miles radius!

I don't really want to have to pay more than $500 for a used engine, maybe up to $600. I know after I get one, I'm gonna replace every single gasket, seal and freeze plug I can get to without tearing the engine apart completely.

EDIT: Oh, and as previously promised, here's a short video of the knocking sound. You can hear it QUITE clearly after the idle settles....

 

$169.99 for just block and head? Hopefully the "guts" also!!

Search Craigslist for one. Lots of guys yank them and go the V8 route.

 

Lol sorry, yeah full block and head. Forgot about CL....