So I just put this engine in my jeep about 2 months ago... Yesterday when starting, I heard a sharp loud bang/knock in my engine bay. It started up and I had no problems. about 5 hours later after being parked for fifteen minute, I started my jeep and got heat soak so having misfires. but at the same time that super loud knock was banging in my engine. I reved up, it went away, when it when back to idle it was still knocking and misfiring.

I know can here that sharp knock when ever I accelerate quikly, but it knocks just once. I'v seen videos of lifter ticks, rod knocks and other stuff and I havn't seen any that knock like this. here' sa video, let me know what you think.


Some times ill here the knock more than once when starting. it seems if the idle is rough, it starts hittin

 

I can't imagine anything inside the engine that would sound like that and not have grenaded that engine after a couple of times.

I would remove the serpentine belt, then start it and run it just long enough to see if the symtom is gone. Start this test after the engine has completly cooled off. Don't run it too long because you are not pumping any water.

 

motor sounds normal. Loud rap sounds like something external

 

By the looks of it, you have an automatic transmission.

Pull the drive plate (flex plate) inspection cover off and check the flex plate to torque converter bolts (4 each) for being loose, cracks in the flex plate, or bolt holes in flex plate being elongated.

 

Hmmm it may sound external on the video, but when I'm right there it sounds like it's coming from inside the engine. I hope I'm wrong... But if it was external, what would it be?

 

I'll try the taking the belt off later today. But the rap is comming from the back center of the engine. It seems to be comming from the top. I'll check the flex plate I did that before When my last engine was havin problems.
Thanks

Oh and just to make me feel like crap, there's a sick xj at school That's never been here:/

 

Get stethoscope.

 

Before I left for school I heard a noise comming from the rear of the engine that sounded like... Well idk how to describe it. Maybe like the sound of an out of balanced fan. It wasn't hittin, but maybe like a rubbing sound... Idk if that helps anybody pin point the cause.

 

idk

 

alright, so I took the belt off and when it revs quick, you still here that slap. now there's a grinding noise almost like a chair being dragged on a wood floor. you can hear it when it was reved up high and then released. here's a video.

it does sound like it could be from the back like a flex plate, but i didn't have time to get under there before work.

 

Alright. Got under it while a buddy revved it, and it does seem to be around the flex plate area... I'll take a look under the inspection plate tomorrow.

 

flexplate

 

so I did check the bolts and they all were tight. so the next step is checking for cracks in the plate? if I can't find any cracks, what should I look for after that?

 

"So I just put this engine in my jeep about 2 months ago..."

Did this engine come with a flexplate bolted to the crankshaft? If not, and you installed the flexplate wouldn't you have seen if the plate was cracked around the crank flange bolt holes.

Here's a couple pics of plates with cracks around the crank flange.

 

I didn't notice any cracks... But I wasnt really looking for them. So it's posable they were there.