tick... tick.... tick..... tick.......Jeep.

[Comanche]

So my 99 cherokee 4.0 I6 has 290,000 miles on it.
I developed a slight tick when cold about 10-k miles ago.
It just started getting progressively worse to the point where it did it at all temps where as before it would be fine after it warmed up.
So I pulled my valve cover last night after doing a fuel pressure and compression test .
All cylinders were within spec in compression/fuel pressure fine.
My rocker bolts were tight, valve springs looked fine, all the pushrods spun by hand and did not appear bent at all.
Pushed down on push rod side of all rockers and did not get any movement indicating a smashed cam lobe.
I turned the crank through it’s paces and did
this multiple times to be sure.
Every thing up top looked pretty solid.
So......today I removed the oil pan and found a nice present inside.
I’ve got the dreaded broken piston skirt sickness on #5 cylinder on the downstroke side.
I contemplated pulling the head , replacing the piston and honing the cylinder bore but while I had access to the timing chain I decided to check it out and it had a crap ton of slack in it.
I figure with this mileage I may run another 10,000 miles before another skirt breaks so I’m just gonna yank the motor and do a complete rebuild, mostly stock but with a couple improvement mods like better injectors, header pipe, cat back high flow exhaust and a cold air intake....oh and a double roller timing set.
I may go with a hotter cam but I’ll see what the machine shop says cause these motors bone stock have plenty of power so with a fresh rebuild this baby will run like a scalded cat anyways and I don’t want to fiddle with what the stock fuel computer can’t handle.

Here’s a couple pics of the nice present in my oil pan.
From what I can see the cylinder wall looks pretty decent.
The fun begins.

 

[Cadcom]

I read an article a few years ago when I was going to rebuild one on stroking one of those rascals. I forget all the details but didn't seem like it would have been hard to do.

This was the kit: https://www.cleggengine.com/stroker-kits/jeep-4-0-stroker-kits.html

 

[Fear Itself]

Just a flesh wound!

 

[Bennyboy]

4.2 crankshaft and a .030 overview yields a 4.7L. I’d keep the stock cam and injectors for fuel mileage. The 4.7 will be real torquey at low RPMs

 

[Comanche]

4.2 crankshaft and a .030 overview yields a 4.7L. I’d keep the stock cam and injectors for fuel mileage. The 4.7 will be real torquey at low RPMs

Ive heard this mentioned before.
Might be something to look into although I don’t really want to buy a new crank.

 

[Comanche]

I read an article a few years ago when I was going to rebuild on on stroking one of those rascals. I forget all the details but didn't seem like it would have been hard to do.

This was the kit: https://www.cleggengine.com/stroker-kits/jeep-4-0-stroker-kits.html

Yeah i’ve read a lot on these.

 

[fz1boxer]

Stroker kit FTW if you want to really up the game stroker kit plus a low boost turbo with intercooler

 

[jeepnuts]

That era 4.0 likes to sh’t number five or six piston skirts into the oil pan

you can replace a piston from the bottom on those, IIRC... just put one in it while you have the pan off and carry on.

 

[Tony2X]

LS swap.

 

[Stampede]

Those old AMC 4.0 and 4.2s are great engines. A rebuilt one stroked a bit would make it feel quicker and I'd expect a modest mileage boost. Nothing wrong with going back with the Jeep inline 6!

I know one guy that had an Cherokee with the 4.0 and he rebuilt it because it leaked oil from the old gaskets. It had 300K on it at the time and still ran just fine, but leaked bad.