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1990 Jeep Cherokee Rod Knock

Discussion in 'General' started by Gino230, Jul 21, 2022.

  1. Gino230

    Gino230 Well-Known Member

    I have a hunt vehicle built on a 1990 Jeep Cherokee platform. It had a dragging brake caliper that lead to an overheat out in the woods last year. We towed it back to camp and after it cooled down, refilled the coolant and everything seemed fine. No oil in coolant, normal temperature, oil looked fine. We used it the rest of the weekend with no issue and then parked it.

    Started it up for the first time today and immediately I heard a ticking, which quickly grew to a rattle at idle. Then I noticed the Oil Pressure is at zero. It still starts and idles, but I'm pretty sure the rod bearings are toast.

    Normally, with an old vehicle like this, I would not mess with it. However, it's got a pretty good chassis setup- lifted with swamper tires and good shocks, platform welded on the roof, light bar system with second battery and isolater system, and a platform welded on the front for dogs (or in our case coolers).

    My brother says complete engines can be had for $700, no idea how hard it would be to do the swap. We're shade tree mechanics that know how to use tools, but I wouldn't open up a car engine. Motorcycle engines I usually stop at removing side covers and clutches.

    Not sure if the rod bearings can be replaced from below via the oil pan? Of course that's assuming the crank isn't damaged.

    Or we could find another Cherokee and swap alot of parts over. Roof platform is welded on but I think it's just welded to the sheet metal of the roof over the pillars.

    Third option is to dump the whole thing and start over- We paid $4k for it and got 5 seasons out of it, so we have gotten our money's worth if I have to sell it. Some mechanically inclined country boy up there (central FL) might buy it for $1000 and do an engine swap or fix it.

    How hard is that engine swap?
     
  2. ChemGuy

    ChemGuy Harden The F%@# Up!

    4.0l six? auto or manual
    Pretty easy to swap on those older vehicles. Hood off. Unhook errythang. disconnect tranny and pull it.

    Lots of videos on YT about fixing and modding cherokees. Use the old engine as boat anchor.
     
  3. Sabre699

    Sabre699 Wait...hold my beer.

    Get a country boy to do it.
     
  4. Gino230

    Gino230 Well-Known Member

    It's a 4.0L 6, manual trans.

    This just happed yesterday, so I haven't had time to do the YouTube research yet! Hunt season still a few months away! But if we're going to do the swap, I will bring it home and do it in my garage instead of under a tree at camp.
     
  5. pickled egg

    pickled egg Tell me more

    Dump a quart of gear oil in and drive the bitch til it ‘splodes!
     
    Dragginass, dtalbott and stk0308 like this.
  6. BC

    BC Well-Known Member

    Get a HP oil pump to start. They are known to have low oil pressure. When I had mine changed, pan was full of sludge as well.
     
    Gino230 likes this.
  7. 88/532

    88/532 Simply Antagonistical

    Rod knocks don’t usually appear overnight. I would guess what you’re hearing is valve train noise due to lack of oil from 0 pressure. Jeep 4.0s have a history of valve train noise btw. Pull the pan, clean. Replace oil pump. Also, you can pull rod caps and check for issues while you have pan off. One at a time, pull, reattach the way it came off with a few drops of oil, torque to spec, repeat.
     
    Gino230 and Boman Forklift like this.
  8. bruceiam

    bruceiam Well-Known Member

    Dropping the pan in the chassis is super easy, as is replaceing the rod bearings. certainly worth a look
     
    Gino230 likes this.
  9. Boman Forklift

    Boman Forklift Well-Known Member

    Assuming you know the motor is bad, While @pickled eggs method may work for awhile, I would go the $700 pull route.

    You may find you can get a place to swap it for a reasonable amount. Years ago I paid a guy 350 to swap a motor for me. It’s not very hard, especially if you have help and extra time. Lately I’ve been working 7 day weeks, so I would pay someone. Remember that someone doesn’t have to be a top quality mechanic, this is an old enough truck with plenty of room to get around.

    If you have a set of wrench’s and sockets you can do it. A cherry picker would help a bunch and save some jacked up backs.
     
    Gino230 likes this.
  10. PMooney Jr.

    PMooney Jr. Chasing the Old Man

    I had one of those when I was a kid, it had a nasty rattle at the front of the engine with a bazillion miles so I replaced the timing chain. It had the exact same rattle afterwards. The torque converter bolts were loose. Sound travels. Lesson learned lol. Fun in the woods! No oil pressure however, torque converter bolt tightening won't fix. Especially when it's a manual trans :D Lol Today's non helpful post, you're welcome Gino!
     
  11. Boman Forklift

    Boman Forklift Well-Known Member

    :crackup::crackup::crackup:

    Made me laugh!!!
     
  12. A. Barrister

    A. Barrister Well-Known Member

    If the oil pressure is zero, I'd look at the oil pump and drive, first. Lack of oil pressure will cause all sorts of things to rattle/tick/knock etc. Hopefully you didn't run it long.

    Once you have oil pressure, then you can see what you need to do next.

    You could also remove the distributor/oil pump drive, and hook up a "screwdriver" to a drill motor, and spin the oil pump to see if it creates any pressure.
     
    Last edited: Jul 21, 2022
    OldSwartout likes this.
  13. Gino230

    Gino230 Well-Known Member

    This is a real possibility. It was only running for 30 sec at idle, and it wasn't long enough to tell where the noise was coming from, just that it was loud, new, and NOT normal. To me, oil pressure zero and knocking usually means rod bearings, but I'm not a real mechanic.

    What you're suggesting is within my capability to try. Swapping engines seems to be a last resort, since prices have gone up significantly from what we thought we could get one for.

    Getting underneath is easy, especially since it has a significant lift. You can almost set up a lawn chair under there. Removing the rod caps doesn't sound too hard, but knowing what a shitty rod bearing looks like is the question. I suppose when I get that far I will send you guys some pics. :crackup:

    Can this be done by switching ignition on, running the pump with the drill motor, and looking for an indication on the oil pressure gauge?

    I am going to dig the manual out today and see where this mysterious oil pump is.
     
  14. Gino230

    Gino230 Well-Known Member

    You had me excited for a minute!

    Reminds me of another time I got hopeful. I was changing the oil in my 749 and out pops a half of a ball bearing. Slightly smaller than a marble. I'm thinking this can't be good. Of course I send pics to MotoCorse and right away they are like "Crank bearings". Dammit! Not wanting to pay to split the cases, I'm looking through all the exploded diagrams of the engine. About 2 AM I see the little ball in the neutral sensor also looks like a marble. I got very hopeful..... So I high tail it into the garage in my underwear and immediately pull the neutral switch out of the back of the engine cases. Nope, ball was still intact. That was another secret sign the universe was sending for me to switch to Yamahas. :crackup:
     
    SuddenBraking and Boman Forklift like this.
  15. pickled egg

    pickled egg Tell me more

    Quick car-part.com shows used 4.0’s going from $250-600. Being 30+ years old, you won’t be getting a 40k mile motor.
     
    Boman Forklift likes this.
  16. Gino230

    Gino230 Well-Known Member

    OK, I saw how to do this by removing the distributor and spinning the pump with the drill.

    Question is, how do I tell if it's creating pressure? If the pump is bad, sludged up, or the rod bearings are toast, then turning on the ignition and hoping for an indication on the gauge wouldn't work?
     
  17. cav115

    cav115 Well-Known Member

     
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  18. BC

    BC Well-Known Member

    They are know for low pressure from the shitty factory pump. https://www.rockauto.com/en/catalog/jeep,1990,cherokee,4.0l+242cid+l6,1179996,engine,oil+pump,5564

    A good HP pump is $80. I wouldn't waste my time f'ing with the distributor and timing. Drop the pan and change the pump. Most of the time that resolves the issue.
     
    Gino230 and Boman Forklift like this.
  19. ChemGuy

    ChemGuy Harden The F%@# Up!

    I like the way this guy thinks.
     
    BC likes this.
  20. A. Barrister

    A. Barrister Well-Known Member

    As mentioned above, use a mechanical gauge to measure the pressure. Then you know for sure what the deal is.
     

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