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Unread 02-08-2010, 09:30 AM   #16
sdowney717
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1998 ZJ 
 
Join Date: Apr 2009
Location: Virginia
Posts: 702
with rod knocks it all depends how far and how hard and how long it was driven. the rod ends can get hammered out of round and enlarged.
You should pull the pan and check the crank. Get some plastiqauge with new bearings and see how far off they are.
Or you can mic the crank.
I have put engines back together with proper clearances on old cranks and they are ok as long as the oiling system is ok and you dont drive it on a race track.

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Unread 02-05-2013, 09:50 AM   #17
liveatibiza
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I'm curious if the ZJ 4.0 worked in your WJ? I have the ZJ engine already, and the WJ is blown. I picked it up that way for 500 bucks. Money is non-existant, so if I could get that ZJ engine in there, that would be pretty awesome.
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Unread 02-05-2013, 10:09 AM   #18
OverlandZJ
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Quote:
Originally Posted by liveatibiza View Post
I'm curious if the ZJ 4.0 worked in your WJ? I have the ZJ engine already, and the WJ is blown. I picked it up that way for 500 bucks. Money is non-existant, so if I could get that ZJ engine in there, that would be pretty awesome.

ZJ and WJ blocks are not compatible.. you need a "clean slate" block for a WJ or (i think) 02+ TJ engine block.
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Unread 02-06-2013, 07:04 AM   #19
thaBrad
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It turned out to be a broken piston skirt on #5 piston. Found the pcs in my oil pan. So I dropped the axle, pan, took everything off the top. Replaced the oil pump, gaskets, new bearings, new rear seal, cleaned manifold and exhaust, new #5 piston, then put it all back together. Got lucky and first key turn, it cranked over. Havent had problems for 40K miles later. The ZJ engine will not work. Unless you wanna do all the mods they talked about in above posts. With new mounts, I think the oil receiver is different, coil pack mounts maybe? I just know its not the same, it will require alot of mods. I did my fix for $800.
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Unread 02-06-2013, 07:09 AM   #20
thaBrad
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If you're probably doing a non-WJ engine in there....do a Dakota 5.9 or Chrysler 300. Something with more HP and rev. Im sure the ZJ wont mount up to the tranny also.
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Unread 02-06-2013, 09:31 AM   #21
Cirruslydakota
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Wait, you didnt just replace one piston did you? You did do all 6, right?
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Bear - 1999 Jeep Grand Cherokee Laredo - 250,000 Miles, BDS 2" lift, Overland rock rails, Dynomax cat back exhaust, 245/75/16 Kumho KL78's, Rebuilt 4.0 @ 244,000 miles.
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Unread 02-06-2013, 11:10 AM   #22
thaBrad
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Yeah just one, the oil pump went out causing that one to break. But I also had the others checked for cracks or anything and they passed inspection. I just didnt have the money to do the fix, so I did it on the lowest budget. I was lucky my buddy with the parts store let me pay monthly payments in 3 months and did some painting at his parents house. I know what your thinking and I agree, but money talks most of my life and I just didnt have the money.
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Unread 02-06-2013, 01:29 PM   #23
Cirruslydakota
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I can understand the money situation so I feel for you there. I had the skirt break off #4 so I pulled all 6 and found cracks right up to the bottom of the oil ring groove on #3 and #6. Made the decision that I wasn't going to do the job a second time and replaced them all. I think all 6 pistons ended up being right around $200 so that made them the most expensive part of the build.

Sent from inside my 4.0.
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Bear - 1999 Jeep Grand Cherokee Laredo - 250,000 Miles, BDS 2" lift, Overland rock rails, Dynomax cat back exhaust, 245/75/16 Kumho KL78's, Rebuilt 4.0 @ 244,000 miles.
Apollo - 2008 Mazdaspeed3 - Mazdaspeed CAI, Mazdaspeed CBE, Prosport boost gauge.
Velvet - 2005 Ford Focus ST - Wife's ride
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Unread 02-06-2013, 01:33 PM   #24
OverlandZJ
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My WJ also had the cyl 5 broken skirt.

So whats the deal on these pistons? Did Chrysler address this and start using better pistons later in the production of the clean slate block engines?
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Unread 02-06-2013, 03:34 PM   #25
Cirruslydakota
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Nope. Emissions is what caused these issues. Chrysler redesigned the 4.0 in 1998 for the 99 model year Grand Cherokee with a new head, intake and exhaust chamber for better flow, and lighter pistons to help improve fuel economy (less mass) along with thinner compression rings. Oil drain back holes behind the oil control ring is where they tend to snap off at since its the weakest part of the entire piston. The result was a weaker casting than previous 4.0's for the head and the piston. That's why you see the 0331 head cracking issue and the skirt breaking issue. Not to mention I was blown away by just how thin the compression rings were compared to other engines I've built. The new sealed power pistons I put in had a thicker casting around the skirts and instead of the many oil drain back holes they had two large slots 180 degrees apart from each other. The design as a whole is vastly superior to the OEM pistons.

You can see pictures of what I'm talking about here: http://www.jeepforum.com/forum/f310/...p-jam-1381182/

Sent from inside my 4.0.
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Bear - 1999 Jeep Grand Cherokee Laredo - 250,000 Miles, BDS 2" lift, Overland rock rails, Dynomax cat back exhaust, 245/75/16 Kumho KL78's, Rebuilt 4.0 @ 244,000 miles.
Apollo - 2008 Mazdaspeed3 - Mazdaspeed CAI, Mazdaspeed CBE, Prosport boost gauge.
Velvet - 2005 Ford Focus ST - Wife's ride
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Unread 02-07-2013, 04:46 AM   #26
shadsjeep
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I have the same broken piston #5. Gonna replace the pistons with the engine in frame also. Sounds like others have had good luck with this as long as there is no damage to the crank and block.
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Unread 02-07-2013, 05:21 AM   #27
99WJ539918
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My number 5 piston blew apart as well! I swapped in an '05 TJ engine. I just took out the distributer and I was set to go. That and the pilot bearing was removed - the TJ was manual.
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Unread 02-07-2013, 03:42 PM   #28
liveatibiza
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So, I know I'm beating a dead horse, but can I strip the Zj block and put the WJ head/accessories on it? I may have access to machining if needed. I'm just curious if that's possible.
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