• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Ticking/Knock/Rattle that matches RPM 88 XJ


NAXJA Forum User
Running into a rattle on my lightly modified XJ. It happens at idle, quietly, but gets louder and matches my RPM when accelerating. Goes away as I lighten up on the pedal, to the point you can't hear it while coasting in D. Seems to be coming from around water pump, harmonic balancer area. Doesn't feel like there's a difference in power. Things I've eliminated as causes:

-Exhaust leak. I think I've solved all exhaust leaks, from random loose hoses to replacing the whole exhaust line. Unless the intake is cracked or something else is leaking in a dark corner, it's not exhaust related.

-Nothing is banging against the fans.

-Undercarriage isn't the source of the noise (replaced trans mount, exhaust line is good)

It MIGHT be:

-Water pump

-just replaced harmonic balancer. The old one was getting pulled into the front of the engine. No issues with the new one as far as I can tell, but it does seem like the noise is coming from this area.

- About to replace idler pulley and throw on a new belt.

-Something else messed up inside the block/under the block

-About to throw new motor mounts on as well

Big shrug on this one. Don't really know what I'm looking for outside the engine. It would help to see if I'm forgetting any obvious causes of such a noise. Besides this rattle, engine is doing great, nice and quiet. No obvious issues with the transmission- I replaced filter, pan, and fluid recently.
if its an automatic it could be the flexplate. also could be lifters?
try using a really long screwdriver as a stethoscope. and place it on various areas of the engine until its the loudest.
Those are on my list to look at as well, but as far as listening goes, I don't really see the point. I'd have to pull the engine apart to confirm anything anyways. "It knocks in the front" okay, gotta pull off the whole front. That's not really diagnosis, just bull in a china shop stuff.
Since you're going to change the belt, take it off and start the engine. It's OK to run for a few minutes.

If you don't hear the knocking, it's one of the belt driven components. Shut the engine off and manually turn every pulley. Look for any wobble, end play, rough turning.

If it's still knocking, the long screw driver/stethoscope will magnify the noise so you can better isolate the area better than "from the front". With the belt still off, engine on so no spinning objects nearby, you can listen around the timing cover, water pump, even the oil pan. Check the cylinders (on the passenger side) and the valve cover.

Watch the water temp so you don't overheat. Shut it down, let it cool, and continue as needed.
It seems to be coming from around the harmonic balancer/oilpan. Please, please, don't let it be my crankshaft or something I'll have to take apart the engine to fix. I don't have time or money to deal with it until late winter/next summer.
New parts are not necessarily good parts. That seems to be the case more and more often.

I would suspect that something is wrong with your new balancer, or perhaps something went wrong with the install.

If I were in your situation I would get a new timing chain and rubber snubber (whatever they call that piece inside the timing cover) and open up the front of the engine.
Would you recommend a new harmonic balancer as well? I just bought it from Advance, didn't really do any research on it. Let me add an important detail I forgot to mention before. The previous balancer was seemingly being pulled into the front of the engine a bit. It's why I replaced it, I thought the rubber was toast and it got too close. Could it be a sign of something else?
Do you have a manual transmission?

I would wonder if your crank thrust bearing is shot.

Can you move the crank forward and aft? Probably need to use a bit of a prying tool. Be careful not to pry against anything that could be damaged, like the timing cover.

That would be a worst case scenario.

I would not rule out the new balancer being bad. DId it go on with a proper interference fit? I would be checking the crank keys. Could they have fallen out during the balancer change? (Mine have always been well gunked into place, but I imagine the situation could be otherwise.)

You are going to have to look for clues. Could end up being as simple as a loose fan shroud or some such thing that had to be moved in order to do the job.
It's the AW4 transmission. I recently did a filter, pan, and fluid change. I was going to do the oilpan and rear main seal soon, this has basically been a guts restoration job since day one. One more mystery to solve.

The balancer I pressed on with a bunch of washers and a slightly longer bolt. I was pretty careful not to strip it our or push to far in, then I torqued it down to about 80 ft lbs... that's what the Chilton's said to do I'm pretty sure. It hasn't been pulling against the timing cover since then from what I can tell, no noticeable wobble. I could try retorquing, or take it off and put it back on. If like you say I just replace the timing set/chain I'll be doing that anyways.
I thought my 1994 XJ was going to throw a rod the knock was so bad. It turns out all 4 bolts holding the torque converter to the flexplate were backed out. After adding some blue Loc-tite and tightening, the engine sounds like a sewing machine it's so smooth.