If you're really lucky you may be able to just replace the bearings but if the crank, rods, or bearing blocks are scored the new bearings will only last a few thousand miles. If you are paying someone to do it there likely won't be a major difference in price (probably a few hundred $$ less) for just replacing bearings or a full bottom-end rebuild (if the shop will even just replace the bearings, many won't, due to the risk of them failing again).


$1500 isn't a bad price for a bottom end rebuild (I assume just the bottom end since you state the head was recently replaced) at a shop, if you're up to replacing the engine yourself you can probably find a low mileage used one for less than $500 or a new (remanufactured) short block for a little over $1000.

 

thanks for the reply dmill89. So I took the thing into a THIRD mechanic, and he was not convinced it was any major engine damage. He pulled the front off and found my timing chain was WAAY loose. He said it moves about 8 degrees either way. I had thought this could be my problem but other mechanics months ago dismissed it. I guess this could explain: misfiring on occasion, rough idle, knock noise even with heavy oil, and the fact when RPMs went high knock went away. Only problem is I won't really know until the new chains on and its fired up.

 

UPDATE: Timing chain was replaced and jeep idles MUCH better. Changed out 20W-50 engine oil to 10W-30 (as MonacaYankee urged). Put in some STP zinc additive as well. Engine is MUCH quieter but a distinct knocking sound is still present. The mechanic who replaced timing chain said chain had 8 degrees of play. Also he mentioned it sounds like the engine does have some piston slap but considering its been overheated its not too bad.


Looks like I'm finally getting to the desert for light off-roading this week, and if anyone cares to know I will be watching my engine like a hawk for any changes. I know a rebuild is in my future but I want to prolong this engines life as long as I am able....any tips would be greatly appreciated.

 

My advice: Run it until it blows or sell it.
I refuse to even deal with 00 or 01 Cherokees.

If I was in your position I would source a known good 00 or 01 motor... Swap the 0331 head with a tupy head.

I saw a 00 cherokee on craigslist and the ad said it had an 05 wrangler 4.0 in it..Could look into what years will swap.

I would spend $1500 on a older running cherokee before I put it into a 00 or 01.

 

Okay thanks for the advice! I am going to stick with this Cherokee... by running it till it "blows" what exactly do you mean? I know that could be a dumb question. Anyway my dad has some serious paranoia for car care and he was the original owner. He kept METICULOUS records of everything and babied the crap out of the jeep. I would rather keep a can of worms I know than take a chance on another Cherokee.
What is a tupy head...I have read about the crappy 0331 head and the alternative tupy.


Lastly, anybody have any good sources for new motors? I have heard of Alabama cylinder or something but its my first time engine shopping.

 

Run it until it blows means run it until it breaks down. "Tupy" is the stamp on the corrected head after the 0331.

You can baby the crap out of anything and it can still break. The head issue is well documented on the 00 and 01. If anything tell your dad you're scared of it breaking down and see what he wants to do.

 

With the 4.0 that could be another 100,000 miles!

 

Get AAA. 120 Dollars a year for 200 miles. Mine blew and left me on the center divide on a Friday in 4 lanes of rush hour traffic. Cost 90 dollars to get pulled off the freeway. Had 230 thousand on it. Last 40 thousand were hell for that engine. Had the standard 4.0 knock or tick the day I bought it. Good luck.

 

So, Im at about 157,840 miles now and it's still knocking. Just did my standard 3k mile oil change....Valvoline 10w-40 (desert road trip and hot temps expected) and some STP ZDDP additive. Changed all fluids and now the only thing is just the knocking that still gives me some worry but I would guess that its proby just piston slap.


WTF though, after the oil change the knock seems louder (or I'm paranoid) and it SEEMS to quite down at operating temps.




I posted this update because it bothers me when I research a problem and nobody says what the heck happened - even if nothing happened. So yah if somebody knows why the knock would be worse with fresh oil I'd love to hear it otherwise here's the update: nothing has happened.

 

Update to the update lol:


Did compression test (had weird stumbling at idle and some misses, especially in drive when stopped and under AC load)
All 6 cylinders within 10 PSI of each other (at both 3 and 4 cranks) and averaged at about 150 PSI with 3 cranks.


I'd say it went well. New plugs and TPS and IAC and the thing idles better than I can remember it idling in a long time. I also backflushed all 6 injectors but replaced inj #2 (constant CEL code for #2 injector). Plus some seafoam in fuel tank.

 

If I was looking at an xj with 157k I'd be more concerned if the thing seemed too quiet. 4.0s with miles make sound.

 

Yah I'm getting that sentiment from many folks. I'll just see how it goes. I'll post updates if anything happens or not

 

I get a real bad rattle at high rpm just before auto tranny shifts on my 91. I attribute to 200,000 jeep disease. May be lifters, someone said exhaust at headers??? It's a jeep thing.