MY 91?

WOW I REALLY LIKE THESE JEEPS! AFTER BUYING A 91 LAREDO FOR 700 I INSTANTLY FELL IN LOVE SO I BOUGHT MY WIFE A 99 G.CHEROKEE ...THANKS FOR ALL THE HELP ON HERE . ON TO MY QUESTION WILL A 96 4.0 FIT IN MY 91? IF SO ANY MAJOR ADJUSTMENTS NEED TO BE MADE AND SHOULD I GO AHEAD AND CHANGE THE OIL PUMP REAR MAIN AND VALVE COVER ? ANY ADVICE WOULD BE GREATLY APP.

1) Relax. Breathe. Please don't type in all caps - it's the equivalent of shouting online, and gets tedious to try to read...

2) The engine blocks will be the same, but the 1996 cylinder head will not have the hole drilled and tapped for the coolant temperature sensor at the driver's side rear of the cylinder head. You can swap the 1991 head onto the 1996 block without any trouble.

If you have the engine out, the changing the oil pump and rear main isn't a bad idea. Might as well, y'know? Also, if you don't know what shape they're in, you will when you're done.

Valve cover gasket you'll probably end up doing anyhow - might as well.

Get the one-piece moulded rubber oil sump gasket (1996 and up, I think. The Fel-Pro number will have an "R" at the end, but I don't recall the full number) whichever block you use, since it will fit all the way up, and will save you wrestling with the thing.

Apart from that, I foresee no trouble with the engine swap.

Oh - and for your Grand, you might want to look around at www.nagca.com (.org?) and see what tech is there specific to your other rig.

Thanks for the advice on the motor and CAPS didnt mean to just forgot...so i will have to change intake also? another quick one i pulled engine from 91 ...it had a nasty knock so i looked and ill be "bleep" if my exaust wasnt cracked...do you think that could have caused me to think it was a knock? 148,000 miles great oil pressure and it just happened all of the sudden ...

sampleman said:

Thanks for the advice on the motor and CAPS didnt mean to just forgot...so i will have to change intake also? another quick one i pulled engine from 91 ...it had a nasty knock so i looked and ill be "bleep" if my exaust wasnt cracked...do you think that could have caused me to think it was a knock? 148,000 miles great oil pressure and it just happened all of the sudden ...

Click to expand...

There, that's much easier to read!

It's possible - and if your exhaust is cracked, check your engine mounts as well (all three of them.) If you replace one, replace all three - or the two old ones will fail the new one all the faster!

An exhuast leak like that can present as a knock -I thought I had a rod knock one time, I was working on something else, and noted that my collector nuts were loose. Tighten them up - no more knock!

You should not have to swap intakes when working with various generations of HO heads - you cannot swap between RENIX (1987-1990) and HO, tho - the ports are in different places. I'd use the 1991 intake with the 1996 engine, so you don't have to swap fuel rails or anything like that.

However, having had a couple of 4.0 heads off before, I have found it rather easier to strip the intake and disconnect the exhaust at the collector, unscrew the cylinder head, and remove the head and manifolds as a unit. Then, service the manifold gasket on the bench, and install the head and manifolds as a unit. Granted, I'm fairly large, so I have trouble reaching the bottom back manifold screws, and I can lift the head and manifolds out lone-handed. If you're not sure, have someone help you - that thing is heavy! You'd also be well served to get some 1/2"-13 threaded rod, cut off two bits about six inches long, and use them as "alignment pins" in opposite corners. Screw them in about four thread's worth, set the gasket on them, set the head down (gently!) and put the rest of the screws in finger-tight only! Remove the two alignment pins, put in the other two screws, the do the following (you're working from the driver's side, for reference.)

1) Remove the driver's front screw and coat the threads with LocTite PST, plumber's Teflon paste, or equivalent (it goes into the water jacket.)
2) Working from the "top centre" (as you're looking at it,) torque the screw to 40 pound-feet. Go directly across the head for the second, and work outwards in a clockwise spiral. (to 40 pound-feet)
3) Reset your torque wrench to 100 pound-feet, and repeat.
4) Reset your torque wrench to 110 pound-feet, and repeat. Omit the driver's side front screw (the one you put Teflon paste on) for this step.

Your manifold screws should be torqued to 21 pound-feet (as I recall...) and use either LocTite #272 or nothing. Replace the screws you took out with SAE Grade 5. Make sure to reuse those little "dish" washers under the screw heads - they're important!

Cylinder Head Screws - if the heads have paint marks on them, throw them away. If the heads do not have paint marks on them, paint them when you're done (any colour - just so it shows up. Automotive touch-up paint in the "brush bottle" is just fine for this.) If they have paint marks, they have been torqed twice already, and should be discarded (since they may snap the third time!) If you're not sure, get new ones.

If you need torque specs for anything, you can go to my site and check out the Tech Archive - there's a torque chart up there for the 1991 XJ/MJ/YJ/SJ. I haven't done the "system-specific" charts yet - you know, for engines, transmissions, axles, and the like.

Exhaust collector nuts should be 3/8"-16, and you should be able to find those in brass locally (which will be far easier next time, won't rust, and will hold up better down there than even Stainless Steel.)

thank you very much ...

Is your 91' a AW4 auto. tranny? If so you might want to check out your flexplate for cracks. When they crack they can sound just a rod/main bearing on the way out.

it was good my dad said he didnt think it was knocking sounded different than knock...148,000 seems awful soon for a 4.0 to go bad... i have a 96 4.0 but would like to save it ... it is a aw4

Remove the inspection cover and check the flexplate bolts for tightness. Use a long pry bar or screwdriver and pry (VERY CAREFULLY) on the flexplate and look for cracks, use a bright light, they are hard to see, turn the flexplate as needed to do 360* inspection.

My 1991 XJ had a serious 'knock' that would go away under engine load. (I hit the gas to try and pop the little sucker, yeah, I was mad.) It turned out that the bolts that held the torque converter to the flywheel were finger-turning loose!

You can check them by removing the inspection cover and using a socket on them. If they're easy to move, then pull them, clean them, lock-tite them and replace them. (It helps to have someone who'll turn the engine/hold it from turning with a big socket and a breaker bar on the crankshaft pulley.)

Nice score on the Jeep!

well i do have the motor out already...the flex plate does look good i will inspect closer tomm. as i do recall the bolts were not as tight as i thought they should be i could hold the hd and turn bolts with wrench with not much effort