[dorkpunch]

Hi all. Just picked up a '94 Jeep Cherokee for 250 bucks. Automatic, 180k miles, nice cold a/c. Body and interior are great, engine not so hot. There is a nice rattle/knock that appears to be coming from around the number 1 and 2 cylinders. Nice flecks of metal, both coppery coloured and aluminum on the dipstick. he said he hasnt changed the oil in a long time... Soooo. What would be the first thing to give out on one of these motors (6 cyl 242)? I think i may have a line on another motor, but how hard are they to pull? I have a lot of experiance wrenching, mostly on smaller stuff but i have done a couple of auto engines in the past. Thanks all for your help!

[mideerhunter]

These engines are pretty reliable, there are some people on this board with over 300,000 miles on them and still going strong, as long as you do regular maintanence and don't constantly beat on the motor it should run a long time, but what you are desrcribing sounds like bad rod bearings, or mains or something, I'm not real sure, but i had rattling noises, and it sometimes comes from loose torque converter bolts, a pretty easy way to narrow down which cylinder or cylinders its coming from is, when the engine is off, pull the first plug wire off, start it up, if it gets louder with one of the plugs off, thats your problem cylinder, I don't think this could create any harm, but don't mark me by my words, I read it in the haynes book and the naxja forum, but it sounds like one or more of the bearings are bad if u have copper colored metal flakes, becasue I know you can tell if the bearings are bad by looking at them and a copper color shows through, but anyways, sounds like the engine is in need of a bottom end rebuild, or a new motor, some people will recommend getting a stroker with using the existing engine block, if you search on this forum you will get tones of hits, but I have read a lot of people recommend getting a decent boneyard motor for 500 or less and it is a lot easier to just put in a new one then take it out and rebuild and put it back in, I have never had any experience with that sort of thing, but the 4.0's aren't something that is a troublesome motor, yeah they do have problems, but in my opionion the 4.0/aw4 was one of the strongest combinations DC/Jeep made, usually the water pump goes out between 130,000 to 180,000 usually, and thats about it, with regular maintance it should run a long time, others will chime in shortly i assume with more detailed information, but good luck with you xj!

[dorkpunch]

thanks for the help. I tried the spark plug idea, didnt seem to make much difference in the amount of noise coming from the engine. pulled the valve cover off and everything looks fine there. One question- there seems to be a lot of rust on the engine oil dipstick (although no water in the oil) and some type of sludgey residue around the neck where the radiator cap goes (on the inside). Is it possible its been submerged once or twice before?

[mideerhunter]

I'm not sure what the sludge is caused from, I know what your talking about, my old f150 had it that was given to me, I think its from the coolant not being changed out and flushed like it should and gunk just building up from there, but these 4.0L's are noisy, you can get a lot of noises that mimic rod knocks or a similiar noise and the engine is really fine, pulleys, water pumps, sticky lifters, cracked exhuast manifolds, loose torque converter bolts, piston slap, even types of oil filters can have an effect, btw what is your oil pressure, the factory specs are 13 psi minimum at a hot idle, and 37 at over 1600 rpms, if its under that you have a good chance its bearings, but if its over you might have one of the other problems i described since oil pressure relies on the bearing clearances, and if you have good oil pressure that means your bearings are still good or not worn out too bad, but don't always trust the stock oil pressure gauge, they fail and are faulty ALOT, so when in doubt always check with a mech. gauge, but overall I don't think an engine swap would be too difficult if you labeled everything correctly and what not, I know the 4.0L's are very heavy though, but good luck!

[dorkpunch]

the oil pressure was supprisingly good according to the stock gauge, dont remeber the exact numbers. the only thing that concerns me is the amount of metal chunks on the dipstick... at first i thought it was a cracked manifold but listening with the screwdriver would imply its inside around #1 or #2 cylinders...

can you get the oil pan off without removing the engine?

[mideerhunter]

I think you can get the oil pan off without removing the engine, I know its a pain in the butt though and it helps to move the axle as far forward and away from the pan as possible, also, what does this metal look like and where?....If it looks like strands, like shavings about 1mm long or slightly longer at the tip, usually the dipstick is magnetic, i could of sworn i had the biggest engine problems for a long time because I would always get this metal on my dipstick, what it was, the dipstick was shaving off the dipstick tube and metal sticking to the dipstick making it look like the metal was in the oil, at a oil change i cleaned it all out of the tube, oiled it a lil, and am very gentle with it and haven't had it come back for over 4 oil changes now, just a quick thing to look at, i figured it out by sticking the dipstick in the tube half way or just before it actually touchs oil and pull it out with no oil on it and if theres metal on it, its a good chance its from the tube