My son has a 2002 Jeep Cherokee with a 4.0 6cly. About a too weeks ago it started making clicking noise. He had new lifters in stalled and new rockers kits in installed. still making the noise. What could it be? It has about 120,0000 miles on it.

This is hard to diagnose without more details.  Typical valve train noise comes from worn lifters.  However, a loose worn timing chain can cause a similar noise.  If the Jeep has an automatic trans, loose bolts on the torque converter can make a “rod knock” sound as well.  I would suggest checking online with some of the “ask the mechanic” sites specifically for Jeep.  There may even be Jeep repair blogs.  Most vehicle models share the same problems and you may find some documented history on this particular issue.

Many times replacing lifters w/o replacing a cam will produce noise.  The lifters and cam wore together, now new parts are mated to an old part and can cause problems.  That is one of the reasons why when you take lifters out of an engine to do a valve job you return the lifters to the original location if you are not replacing them along with the cam.

AD

My 1996 Jeep Cherokee loves MMO!  I don’t know what it is, but acceleration, idle, and general smooth performance are so noticable when I run MMO v. when I do not (which is not very often, just when I need to fill up and forget to put a bottle under the seat).

I have owned 3 of the 4.0 inline sixes with, eventually, the same tick problem (at least it sounds like what I have experienced). What I have found in every single case is that the lifter bores are worn and the lifters will tip slightly, causing a tick. The worst one I had would actually go away if you just shut the motor off and restart it, apparently allowing the lifters to re-set in their bores. After trying many oil combinations to ease the problem I finally found that, in a 6 quart system, use 4-1/2 quarts of Phillips/Conoco synthetic blend motor oil, 1 quart of Lucas Oil Stabilizer, and 1 pint of MMO or Seafoam. Sounds weird but I tried Mobil 1, Maxlife, Amzoil and Casrol GTX with no help. After talking to a man that owns a parts store nearby, he said he owned his own service station for 30 years and that also was what he found to work on the Jeeps. I do agree with the other post here who stated that the camshaft should be replaced, they do wear-in with the lifters and don’t forget that the worn cam will also increase the overall valvetrain clearances thus causing a tick.