Not your average engine knock

[laredo]

Okay,Just got my compression tester. I've never done a test before but I followed a couple write-ups I found online. Here's what i got.
I ran the Jeep for at least 20 mins until it was hot.I then pulled all the plugs and pulled the asd and fuel pump relays. Hooked up the gauge and got these for readings. I did 5 cranks each time. I did two tests on each cylinder.

Cyl 1) 170/170
Cyl 2)150/150
Cyl 3)180/180
Cyl 4)180/180
Cyl 5)180/180
Cyl 6)180/180

I then stopped for about 15minutes to talk with my neighbor about the noise. I went back to the Jeep and redid the test on cyl 2 since it was the lowest. Engine was still warm though. I got 180 both times. I didn't bother doing a wet test since they were all within range.

Listened with the stethoscope for the 20th time while my wife was keeping it at 1500rpm where the knock is most pronounced.It's definitely loud listening through the oil pan however I still think the actual knock noise is loudest when I put it on the bellhousing at the flexplate.

What's next???? :dunno:

 

[Crawler]

Dude...

Did you watch your mechanic?
Can you tell if the inspection plate has really been off recently?
Either way, it's an easy enough job to do... take a look for yourself... he might have missed it!

Use a big standard screwdriver in the teeth to rotate it. Check ALL of the bolts. Look at ALL of the flex plate.

 

[laredo]

I didn't watch my mechanic but I absolutely trust them. They mainly only work on Jeeps and I've been going there for 15 years. I inspected the plate briefly myself but I just bought an endoscope so that I can hopefully see closer towards the center bolts.

 

[DaKing]

I also used an endoscope on my phone. Got it on Amazon ~$30 or so.

But I did not need it. I could clearly see the shiny cracks as I rotated the engine. With the plate off, you can see to the center on the plate. You need to take your time, and inspect it carefully.

If it is cracked, you need to pull the motor or drop the trans.

I just ordered my replacement plate. Pulling the Transmission right now (Well, not exactly RIGHT NOW, Right now I' typing this.)

 

[DaKing]

I pulled my Transmission today,here is what I found:








Center totally cracked around.

My jeep sounded EXACTLY like yours.

 

[laredo]

Damn, that is one hell of a crack. I've seen some do that around the center. I just don't think you can see up around the center where yours cracked without dropping the tranny. That's why I was hoping the endoscope could see up there. Isn't there a spacer that goes over the center bolts as well? Thanks for posting and good luck finishing the job. Do you know what caused it to crack? Bad motor mounts? I'm probably going to inspect it again on Thurs. I'll have the day off and it should be like 60 up here in Mass.

 

[DaKing]

I agree, I did NOT see that round crack when the trans was bolted up. I did not notice it with the endoscope either. What I did see was a few fine shinny cracks, and that "oil" like marks spun from the crack. I wondered what that was, could not tell when trans was bolted up. So, maybe you can remove the inspection plate, and look for "oil" or black stuff being spun off. You can see it's coming from the crack.

Yea, the space was missing. That is supposed to spreed the load, and prevent the cracking. I ordered another one too.

I think it happened from the missing spacer, or loose torque converter bolts. I can see wobble marks around the converter bolts, so they wore loose at one point.

I'm about 90% sure your issue is a cracked flex plate. The video you posted, it sounds exactly the same. In my case, the sound went away when put into gear.

 

[sidriptide]

i'm not going to discount the flex plate as the culprit because the harmonics can transmit in strange ways.
i'm inclined to think it might be piston slap in the lower cylinder.
i had a 99 with 70K miles on it and it has what i called a "random" mid temp-range knocking. the most obvious time i heard it was when i'd start it up after it sat for maybe 1 to 2 hours. engine still warm, mid range on the guage. at idle i'd hear a non-rythmic knock that would go away above 1500 rpm at that temp, seemed inaudible when cold or hot.
stethoscopes screwdrivers and hollwo copper tubes all pointed me to the bottom of cylinder 5 and 6 and after 3 test drives with the dealer service manager in the passenger seat i got him to acknowledge the noise.
warranty required full tear down and measurement of the cylinder bores to check tolerances just to get warranty approval. it was a gamble but it paid off, i got them to replace the engine because 5 and 6 were beyond spec.
ive also had a flex plate break in the same "circle" as the previous post and to me they had similar sounds but very different characteristics under different temp ranges and loads.
obviously the flexplate is the easier one to trouble shoot visually. i'd put the effort into checking that in-depth because a flexplate failure can become catastrophic if left unchecked. if that turns out to not be your issue you are better off just leaving it alone unless you are chasing some kind of warranty.
stop trying to flush your engine and clean out whats probably not really a problem.. you are obsessing over it and it just might be making you a bit crazy.. we've all done it to some extent, myself included.
the only way flushing is going to hurt your engine is if it is really sludged-up and you clog the filter and leave it that way...
piston slap doesnt mean your engine is bad, or short lived.

also, stop googling the "best" oil for your 4.0L. debates about the "best" oil for your car lost their credibility in the 80s. even cheap store-brand oil now is far better than anything available 25 years ago. and oil analysis is over-rated and given more credibility than it deserves because it is mostly mis-understood. i do know about analysis and it a great tool for an oil company to use to sell their product because it picks up a few more PPM of crap than "the other guy's" oil... but the reality is they ALL do a good job of cleaning an engine and keeping it that way. same goes for the MMO in the crankcase, unless your engine is really gunked up with crap it's really just snake oil. my thought is if this low-milage rig had an engine full of sludge you wouldnt have grabbed it when you had the chance..
use what YOU think your rig likes, that is the real benchmark that matters.
i apologize if this came across as a "rant" that wasnt the intention, i got called away a couple times to do real work here in the office... i just didnt want to go back and rewrite the whole thing.

 

[laredo]

Sidriptide,
I didn't take it at a rant at all. That's the same feeling I had about the noise and how I could go nuts trying to trace it. When I was looking into it more I kept hearing not to ignore it, it could be this,it could be that,your engine is on it's way out, just live with it they're noisy engines etc. I was noticing while watching some engine noise videos that some were updated with what the noise ended up being. It was the ones that didn't sound that bad and ended up blowing a rod are the ones that had me concerned. I wanted to do my best to be proactive and hopefully fix it before any more damage,if any,occurred. I'll really inspect the flexplate again and other than that I'm all out of ideas. It hasn't really gotten worse in the past 6 months but I've also only driven her about 2k miles. Thanks for chiming in.

 

[old_man]

I don't see the big spacer/washer on that cracked flexplate.