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Unread 11-26-2012, 06:20 PM   #1
rick2
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4.0 liter in line 6 piston question

just wanted to see if any one knows why the 4.0 liter. mine being a 1999 are breaking piston skirts my number 6 piston did it....... and when i'm done with it will any other ones do it

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Unread 11-27-2012, 06:35 AM   #2
mdm
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My opinion is that Jeep built a loose engine. There is too much clearance between the piston and the cylinder wall. This causes piston slap which leads to broken pistons. I think a lot of what people think is lifters ticking is actually piston slap. When you pull the piston do some measuring and you will probably find that you will need to bore at least 0.010 over stock and use oversized pistons.

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Unread 11-28-2012, 04:11 PM   #3
mike77kurth
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My 99 wj did the same, I ended up replacing all six. Yes it has 200k, but I was not expecting the pistons to "wiggle" in the cylinders or for the ring gap to be over 1mm. broke a ring while installing the last piston... back to waiting for parts. Been at it just over a month

Also debating if the wife messed up a brand new piston enough to pull it again. She did not use the rubber part of hammer when "helping"
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Unread 11-30-2012, 08:51 AM   #4
halo26
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Mike77 - Did you machine your block/measure before putting in new pistons or just drop in stock sized one? I'm grearing up to do the same thing and was Not planning on machining, but a few people have scolded me about that :-)

Also, what else did you replace "while you were there"? ( rod bearing, etc).

Cheers!
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Unread 11-30-2012, 09:13 AM   #5
mdm
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Quote:
Originally Posted by halo26 View Post
Mike77 - Did you machine your block/measure before putting in new pistons or just drop in stock sized one? I'm grearing up to do the same thing and was Not planning on machining, but a few people have scolded me about that :-)

Also, what else did you replace "while you were there"? ( rod bearing, etc).

Cheers!
You need to do some measuring in the cylinders to determine what you need to do. It's pretty unlikely you will be able to just drop stock size pistons in the holes if you want to have proper clearance. An oversized piston will require the cylinders to be bored. If the cylinders need boring, I'd have the cam bearings replaced while it's at the shop. I'd also consider having the main bearing caps align bored. Have the crank checked for journal wear. Excesive wear may require machining and the use of undersized bearings. You might consider getting all the rotating parts balanced. Do a good inspection of the push rods and rocker arms.
Oil pump
Water pump
Main bearings
Rod bearings
Cam bearings
Freeze plugs
Lifters
Timing chain & sprockets
Full gasket set
Head work?
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Unread 12-03-2012, 09:57 AM   #6
mike77kurth
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Sadly, i did not machine the block. I honed the walls and spent every night cleaning with a lot brake cleaner and a toothbrush. Ring gaps and bearing clearance were all within specs. Of course people are going to tell me I should have, that's fine. I invite them and their checkbooks to come do the machine work.

As for what I am replacing:
piston heads and rings,
rod bearings
rear main seal
re-ground the valves
thermostat (I dropped it)
Oil pump and pick up
all gaskets I touched
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Unread 12-04-2012, 05:04 AM   #7
halo26
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That actually makes me feel a bit better, to be honest... I plan on doing the same thing this winter. I'd love to be able to do a full rebuilt, including machining the block, but the money is not there right now.

Your list is spot on with what I'm looking as, as well... Now to build up the courage and start working on it (first time ripping apart an engine)

Cheers!
- Halo
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