4.0 Sounds like a Diesel

Looking for a little help with my 88 XJ. My 173K 4.0 manual creates a fuss upon startup that sounds just like a (big) diesel engine for the 1st few seconds. The noise returns when engine speeds are >1500 rpms and when the oil warms up a bit. I bought the vehicle about 18 months ago, and the engine oil pressure had been running around 20 on the highway and 35 in town. Since the noise started, the pressure indication has been reading 15-25. Only white exhaust is being emitted from the tail pipe, and there is no burning oil smell in the fumes.

This noise seems to have just appeared following a full clutch replacement at the dealer. I had everything replaced; slave cylinder, pilot bearing, resurfaced the flywheel, etc., even replaced the rear main seal. I noticed some good oil leaks the next day and took it back to the dealer to check where the leaks were coming from, and evaluate the noise. They said oil wasleaking from the front main seal, valve cover and air filter housing after covering about 1/2 the filter. They stated that the engine was suffering a lot of blowby and just "tired", although they did not do any compression checks.

After doing a search on "oil pressure", I am not so sure that an engine replacement is warranted as of yet. I am going to replace the CCV tubing to see if that helps/solves anything. The noise only became apparent directly after clutch replacement. It is definately an engine noise, not related to the clutch. I also want to perform a compression check. Is there anything else I should concern myself with before looking at an engine replacement?

try searching for valve clatter, i think there are a few threads about this...

also search "piston slap"

Thanks. I searched both subjects. It doesn't sound as if piston slap is the culprit, as the sound does not go away when the engine warms up and the noise is anything but slight. When I start the engine, the clatter is loud enough to raise the eyebrows of people standing next to the engine, and has turned the heads of people standing 20-25 feet away. I can audibly hear it when the engine is revving near 1500 rpms or above.

One thing that has me bamfoozled is that this noise just appeared. In my experience, a wearing engine part will start to make noise gradually, with the noise increasing with wear until failure. Has anyone else experienced sudden rash noises?

Hmmm, no way you'll ever be able to prove it but..... I have a sneaking suspicion that whoever at the dealer took the Jeep out for a test drive after putting the clutch in might have decided to test it out real good and pull a few 6,000 rpm shifts and did some major damage. Sounds like a rod knock to me from your description. Hope I'm wrong though.
Mike B.

Mine had a pretty severe rattle noise from the engine for over 2 years. I have numerous Jeep techs tell me it was normal, but I had yet to hear another like it. The noise was there over 1500 rpm, anytime. Kinda sounded like steel ball bearings in a tin cup. I removed my oil pan to do a rear main, and found a ton of rubbery crap in my oil pickup. Looked around and found my timing chain very loose. removed my front cover and found my chain was rubbing my timing cover. Inside the cover is a rubber 'snubber' on the slack side of the chain. The crap in my pickup was the snubber. It tore it to bits and ground the retainers off the timing cover. The Jeep dealer said to find some good rubber super glue, clean the cover, and glue the new snubber on. I did so, and it's been working great since. My oil pressure has also gone up since my pick up is no longer mostly blocked.

See the link for more info:

http://www.naxja.org/forum/showthread.php?t=7622

Good luck,
Steve

After searching the archives some more, I highly suspect that the rod bearings need replacing. It is very odd that two of forum members describe the exact same phenomina after having their rear main seals replaced. At any rate, it sounds like I need to drop the oil pan and take a look at what's going on in there.

Can someone describe the difference between a worn and spun bearing? One seems to be easily replaced, while the other sounds like resurfacing the crankshaft may be necessary. While I have mechanical abilites, my knowledge can definately be improved. Nothing like baptism by fire.

I still need to do a compression check and check the plugs to help determine the shape of piston and rings. Are there any other checks that I should/can do to help assess the overall condition of the engine? Depending on the results, I may just replace the entire engine with a remanufactured motor.