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Rod Knock?

S

Samson04

NAXJA Forum User
Location
Taylorsville, KY
I have a 98xj, 4.0, AW4, with 180K on it. Just went out to lunch at work and noticed a noise coming from the engine bay. It sounds like a rod knocking. It does get faster with revs but it doesn't get louder. After opening the hood, it is coming from the front of the engine definitely. As a matter of fact, it sounds like it is coming from the water pump area. Any chance that it is the bearings in the water pump pulley, because it does have some wobble to it? Any chance it's not a rod? I have had this rig for over 3 yrs. now and I change the oil regularly and I was really hoping to get 250k + out of it. Any suggestions?
 
Noises in the engine bay can be deceiving as far as locations are concerned. I've read on previous posts that Joe recommends getting some vinyl tubing to put against your ear and try to isolate the noise. You could have a loose or cracked flexplate causing a knocking sound. How is your oil pressure? Have you been going through any coolant? If it is internal engine you could also have a stuck hydrolic lifter or even just a little piston slap
 
I will obviously have to take closer look when I get home, but oil pressure is fine, 30-45 psi, and oil was changed less than 2 weeks ago. Coolant level is fine as well as the engine temp. As far as the piston slap, would it be that loud? I did climb under it and the noise is obviously loudest at the front of the engine. With the hood down, I can put my head in front of the radiator and it is very noticeable.
 
I know when mine is cold there's a definite piston slap I can hear outside of the vehicle, but under load I can't hear it inside the cabin. I do sometimes hear a ticking at idle that I attribute to a sticking lifter. Just out of curiousity, when you chaged the oil, which oil filter did you use? It's important to use a quality filter to prevent dry cold starts which could theoretically be causing some bearing damage leading to a knock. If you do a search on oil filters you'll find plenty of reading. Just a thought.....I think you want one with a rubber nitrile valve and not a paper or carboard one which is important since our filters are mounted sideways.
 
The weird thing about the piston slap is that I've never heard this noise before today. I just would have thought if it was piston slap that it would have been more gradual. As for the filter, it is a Fram Tough Guard.
 
Gheez. Fram's work, that's not the cause of your problem, I spun a rod bearing on my old CJ using K&Ns.

Get a hose and start listening by placing the hose on various parts. Don't need vinyl just use old heater hose pieces lpng enough to keep you a safe distance from hot or moving parts. If you think it is the w/p bearing remove the belt and run the engine. If the noise goes away you have narrowed down the source to w/p or belt, or idler pulley, or altenator, or a/c pulley or p/s, but the look will be narrowed.

Cracked flexplates or loose bolts will make one heck of a racket if you do a stall test.

Rightseatsis' XJ has a small piston slap and has for about 100K miles and still going strong.
 
Well, found the problem. Definitely the water pump pulley, as it has a LOT of "play" in it and it has started leaking antifreeze. Any suggestions on which brand to replace with?
 
Okay, just went to NAPA and bought the water pump and it did not come with the pulley. Is it supposed to? The guy at the counter said he didn't even have a listing in the computer for a water pump pulley for a 98xj. Would this be a dealer only part?

I think I may have answered my own question. The pulley itself doesn't have bearings, the water pump does. Therefore I should still be able to re-use the pulley.
 
Last edited:
Samson04 said:
Okay, just went to NAPA and bought the water pump and it did not come with the pulley. Is it supposed to? The guy at the counter said he didn't even have a listing in the computer for a water pump pulley for a 98xj. Would this be a dealer only part?

I think I may have answered my own question. The pulley itself doesn't have bearings, the water pump does. Therefore I should still be able to re-use the pulley.
Click to expand...

Yep, you've answered your own question.
 
Got the water pump put in on Sat. Apparently some time in this xj's life, someone decided that it would be a good idea to run "Radiator Stop Leak" in it. NOT A GOOD IDEA! There is a "Muddy" residue all over the inside of the hoses, radiator neck, etc. I bought a radiator flush, Is this all I need to do to ensure that this GUNK comes out?
 
Boatwrench said:
Before removing the w/p, loosen the heater hose neck threaded into the pump a little.
Click to expand...
Around here, buying a new one first is a better plan. Kentucky and California have it easy rust-wise.

To flush all that crap out, I would back-flush with a garden hose first (not at full pressure, or disconnect the heater core before going to full pressure, blowing that out is not in your best interest) and then follow the directions on the radiator flush.
 
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