Knocking sound at idle

[ChristopherD]

'97 2.5 auto 141k miles
Knocking/rattling at idle
Runs fine. Just drove it for 3+ hours around the hunting club pulling cameras. Nothing serious at all. 30 mins drive home, did fine. Did notice the oil pressure, just below 40 while driving, drops to about a quarter of the guage at a stop. Problem is when at idle there's is a knocking/clanking sound, similar to the ball in a spray paint can, coming from underneath. I was leaving for work so I didn't have alot of time but best I could tell was it was coming from the oil pan area. I'm expecting the worst but hoping for the best. What do y'all think?

 

[CasperLLY]

Piston slap maybe

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[ChristopherD]

Piston slap maybe

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Would that give any other symptoms other than what I'm experiencing?

 

[CasperLLY]

No, basically a skirt on of the pistons broke off and is allowing it to rock back and forth in the cylinder as in travels up and down. Mine sounds kinda like an old desiel in the winter till the engine warms up

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[AndyG]

Man you can't say that the engine is knocking and nothing serious at all in the same sentence!

 

[ChristopherD]

Man you can't say that the engine is knocking and nothing serious at all in the same sentence!

I meant nothing serious as in riding wise while at the hunting

 

[ChristopherD]

No, basically a skirt on of the pistons broke off and is allowing it to rock back and forth in the cylinder as in travels up and down. Mine sounds kinda like an old desiel in the winter till the engine warms up

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So.....how long is left? Lol.

 

[ChristopherD]

This doesn't go away as the motor gets warmer. I actually haven't had a chance to even see if its there while it's cold.

So.....how long is left? Lol.

 

[Chris]

Does it sound like lifter tick at all? If so, it could be the lifters ticking or an exhaust manifold leak. Both common problems with the 4.0.

 

[ChristopherD]

Does it sound like lifter tick at all? If so, it could be the lifters ticking or an exhaust manifold leak. Both common problems with the 4.0.

It doesn't sound like lifter tick, and I'm sure there is an exhaust manifold leak but laying under the Jeep I could tell it's coming from the bottom of the motor. I'll try to get a video when I get back home

 

[KCsTJ]

If it is piston slap you could preemptively drop the oil pan, unbolt the rod cap and pull the offending piston out.
1 new piston and rings and you have wisely repaired the motor before further damage occurs.

 

[AndyG]

I meant nothing serious as in riding wise while at the hunting

Cool, hope it's ok.

 

[pagrey]

You might check the timing chain. Play between the crank and and distributor, pretty easy to check without taking too much apart.

 

[ChristopherD]

If it is piston slap you could preemptively drop the oil pan, unbolt the rod cap and pull the offending piston out.
1 new piston and rings and you have wisely repaired the motor before further damage occurs.

Can you really do that? I'm not a mechanic but I'm not afraid to go after it myself. But, like the saying goes, I don't have money to just throw at it hoping to fix it

 

[CasperLLY]

So.....how long is left? Lol.

Picture of a broken piston skirt

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[ChristopherD]

You might check the timing chain. Play between the crank and and distributor, pretty easy to check without taking too much apart.

It drives fine, doesn't miss or act like it's close to being out of time though. If there was enough slack there, to be making THIS noise wouldn't there likely be performance issues also?

 

[ChristopherD]

So as I'm sitting here draining water out of my work truck since it's going to be cold tonight in Alabama, I'm rereading all y'all's posts and the only way I can describe the sound is as if you out a steel ball in the oil pan and it has a string loosely attached from it to one of the pistons and you can hear it bouncing around inside, but only at idle. I looked up some videos while I was working and it doesn't match the sound of piston slap. Not ruling it out though. And I'll get a video of the sound here in the next hour or so

 

[Daryl]

Remove the engine belt and start the engine. If the noise is still there and you’re convinced it’s internal, remove the engine oil pan for inspection.

 

[CasperLLY]

Here is what mine sounds like and I believe piston slap. Bits not as loud when warm

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[KCsTJ]

A sound like you describe needs to be found cuz it won't go away and it won't get any better.
I would drain the oil and look for metal pieces. Then drop the oil pan and look for metal pieces.
I bet you find your answer then.