diagnosing engine knock

A few weeks ago my XJ started making a knocking sound. It doesn't do it right away, the engine has to warm up.. maybe 10-20 minutes until it starts making the sound although the last time I drove it, there was no noise. Oil pressure is fine..

So far everyone that's heard it says it definately doesn't sound like rod knock and that it sounds similar to a noise a bad lifter would make. The only thing I've done so far is verify that there's nothing broken/sloppy in the upper valvetrain.

Here's the sound file:

http://www.sph33r.net/jeep/knock.wav

Not easy to tell, but the wav file is a good start! Ususally, but not always, a rod will knock most under load, while mainbearing knock is pretty constant and deeper in tone than that. 6 years ago in a differnt 4.0 I had a very similar sound, I suspected rod knock. On a hunch I pulled the serp. belt off & it was gone. Turned out that the alternator bearings were gone in a strange way causing a knocking instead of a squeal. Try it, you might like it! The others will chime in soon. Also, I would agree that it probably isn't rod knock, but valvetrain noise is a possibility (loose rocker, stuck lifter, etc.) Finally, remember that the speed of the noise will help you find it. If it's at 1/2 engine speed, suspect the valvetrain or possibly drive accesories, such as the alt. At full engine speed, start worrying.

Where exactly were you holding the microphone in that .wav?

The mic was over the engine/to the drivers side where the noise seems to be coming.

Hmm. That's a fairly loud knock. Maybe for starters take a cut down broom handle or similar. Move it around the engine and put your ear to one end- you'd be surprised how well it'll pinpoint a noise.

Have you checked the shaft in the distributor isn't worn? Take the cap off and see if the shaft moves side to side.

JJacobs: I'll try that broomstick idea.

Aardvark: I changed the cap late last year and had no shaft play but it wont' hurt to check it again I suppose..

Well, being that it's over the left side of the engine, you may want to consider that it could be the power steering pump. Listen closely to it. Then take beav's advice and remove the serp. belt. See if you can spin everything by hand smoothly with no resistance. Then start the engine and see if the noise has gone away. Don't let it run too long though, as there will be no water circulating.

Good luck

sph33r said:

A few weeks ago my XJ started making a knocking sound. It doesn't do it right away, the engine has to warm up.. maybe 10-20 minutes until it starts making the sound although the last time I drove it, there was no noise. Oil pressure is fine..

So far everyone that's heard it says it definately doesn't sound like rod knock and that it sounds similar to a noise a bad lifter would make. The only thing I've done so far is verify that there's nothing broken/sloppy in the upper valvetrain.

Here's the sound file:

http://www.sph33r.net/jeep/knock.wav

Click to expand...

I listened to your sound file and it is hard to tell if it is exactly as mine sounded about 2 months ago. I had 190,000+ miles and there was a knock that sounded like it was coming from the drivers side of the engine. The dealership that I occasionally use , had the mechanic check it and iwth his stethoscope he identified the sound coming from the bottom of the engine, through the oil pan. In other words, he put his stethoscope on the bottom of the oil pan and identified it as the loudest.

Turns out it was the thrust bearings, so I had all the engine bearings replaced and the soudn went away.

Hope this helps-

Jeff-97XJ

How long did it take you to get the engine bearings replaced?? I have a nasty knock in my wagoneer that I think is the rear crank bearing and I might as well replace as much as I can when I'm in there...

tthompson10 said:

How long did it take you to get the engine bearings replaced?? I have a nasty knock in my wagoneer that I think is the rear crank bearing and I might as well replace as much as I can when I'm in there...

Click to expand...

I don't know what you mean by how long did it take me to get the engine bearings replaced, I heard the knock for several weeks at the most. The dealership had my XJ in there for 10 days with all kinds of excuses about DC sending in the wrong parts etc. The mechanic claimed he had to invent a "special" tool to get the old bearings out, so I don't know what to believe. I know that I would not be qualified to have identified where the knock was coming from or to replace main bearings.

Hope this helps-
JP

Sounds similiar to what I had......thought for sure it was in the eng....e-1 kept saying it was a rod or bearing............ready for this....it turned out to be the flexplate....was cracked in mutliple places around the bolt holes...replaced...noise went away....good luck..its cheaper than tearing apart the the lower end.