bradleyheathhays

96 XJ here, 180k 4.0. Recently I've had a repetitive knock sound show up. You don't hear it on a cold start but after it warms up there's a distinctive lower pitched knock with a frequency of about 10 times a second, at idle. Seems to be coming from the bottom of the car/engine as you can hear it better from the sides and rear. The normal engine sounds seem to drown it out when you listen from over or in front of the engine. Not sure if the knocks increase in frequency along with acceleration.

Any ideas?

craigjacob1

It could be the timing chain, water pump, or even the flywheel. You will have to use a stethoscope to pinpoint it, or have a mechanic take a look.

Friar Mountain XJ

cruiser54

First thing to do is this:

https://www.cherokeeforum.com/f51/ho...ocking-125547/

Also inspect your harmonic balanceer.

bradleyheathhays

I think you hit the bullseye Cruiser. My knock sounds exactly like what's in that thread video, meaning the flexplate bolts. Thank the gods this is a relatively easy fix.

Would it cause any damage to run with it like this for a couple weeks? I have a more pressing issue with a leaking heater core in my other dang vehicle.

cruiser54

Do not let it go!!

It's a half hour fix with a 15mm wrench and some LocTite.

bradleyheathhays

You're right I'll make the time. Thanks for the motivation

cruiser54

Consider it a digital kick in the ***!!!!

bradleyheathhays

Thanks my friend, I could use that sometimes. Although it took a couple hours I got it done. 2 of the bolts were easy to get out so I'll bet that was the problem. She's still up on ramps with the loc tite curing so I'll leave it like that til tomorrow. Now I can get started changing out the leaking heater core on the old '11 crown vic...at 2am...and 35 F outside. Yeah.

cruiser54

Great!! Hopefully that was the cause. I'll bet it was.Heater cores are rarely a fun job.............