2000 XJ - Knock knock?

[Herzog]

I had to pick up my kid and his XJ on the trailer today, it developed this knock... I'm not super engine savvy but it sounds to me like a possible rod knock or piston slap, especially comparing to other videos with the same diagnosis. My hunch is the piston skirts left the chat.

I'll be dropping the pan soon to verify, but regardless sounds like it has problems. So, question is, bottom end rebuild or just find another engine to swap in? Almost 300k miles...

Note - the noise isn't coming from the top end, hard to tell in the video but the valve train up top sounds good.

 

[STAG]

Slap a Cummins sticker on the back window and run it!

Kidding, but I have heard of 4.0 people successfully throwing in new crank/rod bearings while the engine is still in the unibody rails, not even pulling the block.

 

[Herzog]

Kidding, but I have heard of 4.0 people successfully throwing in new crank/rod bearings while the engine is still in the unibody rails, not even pulling the block.

Yea I've been on a youtube binge looking at similar situations trying to decide what to do. I think it will be a pretty good opportunity for him to learn a lot about his engine either way. Seems like not too big of a deal to rebuild in the bay there.

 

[bryson]

Automatic? Could be a cracked flexplate or something too...

 

[STAG]

Obviously

 

[Mouse]

Hard to tell over the internet. I had an XJ once that sounded similar and we assumed it was a connecting rod bearing. Had somewhere around 300K on the engine. We decided to pull the engine and found a flex plate bolt had backed out and was hitting the block (slightly). tightened it up and it sounded like a normal 4.0 again

 

[Hickey]

Automatic? Could be a cracked flexplate or something too...

That reminds me. I bought a 94 XJ many years ago that had a pretty bad knock. Sounded like a rod knock, but it was several missing bolts on the bellhousing. Replaced some bolts and it ran awesome and smooth. I wish my YJ had that kind of power.

 

[N-Smooth]

I came here to mention the loose flexplate bolts.

 

[Herzog]

Cool, I’ll pull the inspection plate off and check those bolts. That would be awesome if that’s all it was. It does sound lower and closer to the transmission.