Jerry Posted June 8, 2011 Share Posted June 8, 2011 I've been trying to figure out why my motor is making a mild knocking noise :hmm: Are there a set of common noises that the 4.0L makes? Wondering if the forum can help me work out what it is? :bowdown: I'll do my best to describe it! The noise was present when I bought it over 10,000 miles ago. It hasn't changed in all that time and I've driven it pretty hard. The sound only appears once the engine is warm. To me it sounds like slightly worn cam noise but it can't be the cam(?) because the noise is NOT an even knocknockknock it's more like a variable clattering sound. The oil pressure is good so it's not a bearing. Weirdly it gets noisier when I put fresh oil in! Noises are usually masked with fresh lube! I've stethescoped it all over and it's loudest from the bottom end of the engine through the oilpan. It starts fine, idles fine, runs fine, does what it's supposed to. One of my lifters has started ticking intermittently so I'm wondering if it could be lifter related but it's not the "clack" sound I associate with collapsing lifters. What else in a 4.0L can make a soft offbeat knocking noise but not cause any problems? Timing chain? output shaft? Oil pump? I'm not a mechanical numpty but I can't figure this out so it's over to CC wisdom Link to comment Share on other sites More sharing options...
jeep_freek88 Posted June 8, 2011 Share Posted June 8, 2011 This is strictly a guess could you have a cracked head pipe? exhaust leak :dunno: Link to comment Share on other sites More sharing options...
hick92 Posted June 8, 2011 Share Posted June 8, 2011 my comanche has the same noise Link to comment Share on other sites More sharing options...
Jerry Posted June 8, 2011 Author Share Posted June 8, 2011 This is strictly a guess could you have a cracked head pipe? exhaust leak :dunno: Anything on this subject is going to be strictly guessing! :thumbsup: I may have but I don't think the noise would travel down inside the engine? Exhaust leaks are fairly easy to detect. my comanche has the same noise Good to know I'm not alone :D It's partly why I was asking about "Common engine noises", I have heard another 4.0L making a similar noise but it wasn't as loud. I've also listened to other 4.0L's that just purr quietly with very little mechanical noise and definitely no clattering! Anyone else have the same? Link to comment Share on other sites More sharing options...
87Warrior Posted June 9, 2011 Share Posted June 9, 2011 I think I know the noise you are talking about. My 92MJ did it and my folks 93XJ does it, 190K and 130K miles respectively. The donor 99XJ didn't do it with 153K miles. My 03TJ and my fathers 03TJ don't do it, 90K and 120K miles respectively. They ALL have noisey valvetrain. Link to comment Share on other sites More sharing options...
vaquaro Posted June 9, 2011 Share Posted June 9, 2011 Same thing on my 2.5 turned out to be the timing chain :dunno: Link to comment Share on other sites More sharing options...
Geonovast Posted June 9, 2011 Share Posted June 9, 2011 Same thing on my 2.5 turned out to be the timing chain :dunno: 2.5's a slightly different animal with the timing chain. It has a bit more slack than the 4.0, so it requires a tensioner, and those like to die. 4.0 doesn't have a tensioner. I'm not saying that couldn't be the noise, just throwing the information out there. Link to comment Share on other sites More sharing options...
terrawombat Posted June 9, 2011 Share Posted June 9, 2011 My '01XJ with a '98XJ engine in it has a very soft, but noticeable, knocking sound. It has been there since I dropped the engine in two years 30K+ miles ago (has 184K on it now). It doesn't matter if the engine is cold or warm, but it does seem more pronounced when the engine is up to operating temperatures. It definitely seems to be coming from the bottom end, but I've just learned to live with it. Of the many Jeeps I own with a 4.0L under the hood, this one is by far the most powerful and has the best oil pressure so I'm not too worried. My '88MJ Pioneer (4.0L) makes a similar noise - 78K My '92MJ Sport (4.0L) does not make any noises - 240K+ My old '91YJ (4.0L) did not make any noises - 116K Who knows? Someone once told me that if a 4.0L isn't making some strange noise, it's not running right :D Link to comment Share on other sites More sharing options...
87Warrior Posted June 9, 2011 Share Posted June 9, 2011 I think the knock indicates the 4.0 is finally broke in. :yes: Terra - if your 92 isn't knocking yet, it should make it to 500K no problem! Link to comment Share on other sites More sharing options...
Jerry Posted June 9, 2011 Author Share Posted June 9, 2011 Thanks for all the input guys :wrench: So it's probably just a "They all do that sir" kind of noise. Good to know my engine isn't about to explode! CC does it again :thumbsup: Link to comment Share on other sites More sharing options...
shelbyluvv Posted June 9, 2011 Share Posted June 9, 2011 The 4.0L is known for having piston slap. It is probably what you are hearing. Link to comment Share on other sites More sharing options...
Incommando Posted June 9, 2011 Share Posted June 9, 2011 More than one 4.0 has been diagnosed as "blown up" and replaced due to the flex plate bolts walking out and hitting on each revolution. Yes, 4.0's have some piston slap and valve train noise. Many a 5.0 Ford has the same piston slap noise. IMHO it is no big deal if that is what it is... Get a good mechanical oil pressure gauge and run a compression test if you want to ease your mind a bit. Link to comment Share on other sites More sharing options...
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