jtsherrod

Ive never had a jeep but i had an amc eagle for a while. idk why.

Currently have a 2000 grand Cherokee 4.0l

150k came to me with bad head gasket. it would start but could not drive very far. (cyl 6 was filling with coolant and intake manifold was badly broken)

i replaced head gasket and new intake manifold.- engine fired up but sounds bad.

Compression test
1-90
2-0(30 with oil added through spark plug hole)
3-0 (30 with oil added through spark plug hole)
4-0
5-90
6-120

Those are some VERY low numbers.... are my piston rings that bad on 3 cyl or did i miss something??

when placing rocker arms back on i put each cyl to top of compression stroke and tighten down to 19ft-lbs

Not super familiar with this motor but have done some timing work but not on a distributor less motor

Thanks

dave1123

Welcome to CF!

It sounds to me like the engine was overheated enough to destroy the temper in the rings making them lose tension. How did the top edges of the pistons look when you had the head off, in the area around the rings? If the ring grooves started to melt, the rings could be locked in the grooves. This would show as raised metal on the top edges of the pistons. #4 may have a broken ring or a burnt valve. I hate to say this, but I think you're looking at a rebuild, or at least a piston&ring job and a valve regrind.

This engine also has the 0331 head that is known for cracking. That usually occurs between cylinders 3&4 on top inside the valve cover. That puts coolant in the oil destroying the bearings if not caught quickly.

I own one. I've been thru that already. Luckily mine just cracked into an exhaust port.

dgnoj

I'd start with the head. Pull it and have it magnafluxed and vaccum checked. If it's the valves not seating well, the vaccum check will catch it and if it's not cracked you can probably get away with a valve job, or even hand lapping the valves in by hand. When the head is off, check what kind of ridge you have in the cylinders. If you drag your finger nail up the cylinder wall and there's a ridge big enough to catch it, it's probably time to bore it and drop bigger pistons and rings in there.

jtsherrod

the cylinders did not have a ridge on them that i noticed but i wasn't looking to hard i suppose. i did check for the crack between 3 and 4 and it seemed good. I will say i did not have the head decked or valves checked. which ..in hindsight... seems foolish.

im just debating if it is worth taking the head back off and checking it. Id hate to do all of that and have it end up needing rings and a lower rebuild..

dave1123

This is a ancient tractor engine with relatively low miles on it. A vertical engine tends to not make a ridge anyway. You could cut the ridge off with a reamer, pop the pistons out, hone the cylinders to break the glaze, put new rings on the pistons, and put it back together. I would, however, regrind the valves and check the head for flatness. You could even throw a new set of bearings into it while it's apart. This is called an "in chassis rebuild" and works well with this old design. Oh...and put a new timing chain in it too. New lifters are a good idea as well. The only thing you won't do is the cam bearings, but they usually don't need to be replaced at 150K miles. Check the valve rockers for tip wear and the mounting blocks for scoring.

For all practical purposes, you'd have a new engine when you're done.

97grand4.0

What is that you said about torquing the rockers to 19 at top of compression stroke? Is that a fsm thing? Is it possible you have valves not seating because of that? My understanding is the rocker keepers are torqued, but that is not a valve adjustment, at least on mine.
I think you're looking at a head problem rather than a lower block, but it's a roll of the dice. 0 compression on 3 cylinders is too low unless the rings are in the bottom of the oil pan.
I would also chase the threads in the head and replace or at least clean the head bolts, you want to get that 100lbs of torque on them, not only 50 because you're fighting dirty threads. Loose head bolts are not so good for a leaky head.
In fact the more I think about it, you could have weak head bolts from the over heating. I wouldn't try over torquing them or you will break one and then you're really up the creek. First see if you can chase the threads, but if not just pop in some new ones and pay attention to the torque sequence.

dave1123

^^I second the motion!^^ Clean oiled threads and new bolts is the only way to go. The 4.0 isn't a torque-to-yield motor, but the head bolts can get stretched over time.