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WJ 4.0L New Pistons

Old 10-04-2016, 12:19 AM
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Default WJ 4.0L New Pistons

I just bought a WJ. 1999, Black, 200,000 miles. Never had a wrench turned on it. Doesn't know what rust is. Can't find anything wrong with it aside from a wheel bearing and it had the "mystery tick". I got it super cheap because of the tick. I bought it knowing I'd find something I had to fix. Checked the top end, made sure it wasn't showing any signs of the cracked head. I checked the flexplate, looked for exhaust leaks, pulled out my mechanics stethoscope, but still couldn't isolate it. I decided to pull off the oil pan, sure enough:

Broken Piston Skirt.





There's no signs of cylinder damage, so I'm gonna go ahead and put new pistons, rings, and most likely rod bearings.

I've done A LOT of engine work in the past. VW, Porsche, Johnson Marine, Mercury Marine, Suzuki 2 Stroke, Ford, Jaguar, Austin Healey, Honda, Volvo... The list goes on and on.

Only thing is I'm really used to Over Head Cam when it comes to engine internals. The standard system is kinda weird to me. Well new I should say.



So anyway, anybody got any tips? Anything related. I'm a sponge. My brain remembers everything it considers semi important.

That being said, I already know the 0331 head is bad news. I've done my homework, and when I have the money I'll get the TUPY.


But seriously, any advise from personal experience, I'll take it in.

Thanks in advance,

Justin

Last edited by 99Justin4.0; 06-27-2017 at 03:56 PM.
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Old 10-04-2016, 04:55 AM
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Keep in mind that the TUPY head is still a 0331 with nickle added to the composition of the pour. When you check prices, make sure it is complete with valves and springs.

I bought a "Clearwater" head from Odessa for $455 complete with valves, springs, and shipping BOTH ways (core return) and a 5 year warranty against cracking. It's a heavy duty casting that weighs 8 lbs more than the 0331 and most of that metal is over the top of the cylinders. I don't think you'll find a NEW complete TUPY head for that price. It came Fedex Express and I got it in 3 days. Funny the core gets shipped back USPS as scrap metal! You have 30 days to return the core or get charged $100 more, but they're pretty lenient about it.

As long as you've got it apart, why not complete the overhaul with a new cam, gears, timing chain, and lifters. If you're careful, changing main bearings with the crank still in is not that big of a job, add a new oil pump and you've got a new engine for all practical purposes. I know, $$$$ right?

Forget what I said about changing the cam. That stick is almost 3 feet long and very difficult to change with it in the car. At least put a chain in it. Check the rockers for wear and cracking and the pivots for wear also. The rockers tend to crack in the pushrod socket area when they do. Check the pushrods for straightness by rolling them on a flat surface.

Now that I've spent all your money, I'll leave you to it.

Last edited by dave1123; 10-04-2016 at 05:12 AM.
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Old 10-04-2016, 05:06 AM
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Old 10-04-2016, 06:55 AM
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Honestly i would pull the engine and rebuild the whole thing with a new head.Its not the cheapest or easiest thing to do but the best option if you want to keep the jeep a long time.
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Old 10-04-2016, 08:46 AM
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How much of the piston skirt is broken?

It looks like you have 4 options-

1-leave it. Clean out the debris in the pan and change the oil and filter a couple of times. It might just last another 50-100k miles. It's a Jeep 4.0, one of the most robust engines ever made. It takes an act of God to kill one.

2-change out the 1 piston. Here you can do in the vehicle. Pull the head and pan.

3-'mini' rebuild. Once you have gone this far, option #2 on a 200k engine pulling the head and pan, you could do a 'mini' rebuild with engine still in the vehicle as described above- new pistons, rings, bearings, timing chain, oil pump.

4-full rebuild and be done with it.
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Old 10-04-2016, 09:46 AM
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don't you have to hone the cylinders when installing a new piston/rings to seat them? is that possible with the motor in the vehicle and the head installed?
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Old 10-04-2016, 11:24 AM
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Originally Posted by jon-d View Post
don't you have to hone the cylinders when installing a new piston/rings to seat them? is that possible with the motor in the vehicle and the head installed?

Yup they should have some cross hatch on them.
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Old 10-04-2016, 01:27 PM
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I'm pretty set on doing all six pistons. I'm doing as much as I can afford right now. Anything that doesn't require the head off again can wait. If it does, it can wait till I replace the head.

I pulled the pan in like 30 minutes. I did some good homework and knew the axles had to be as low as possible (I just bought my first pair of ramps too...). I knew to put the bolts in cardboard trick to keep them in order, EVERYONE should know that pulling a starter is easier than the exhaust (poor guy on youtube...), and I knew I'd need 2 long extensions.

The jeep did run perfect. It had good consistent oil pressure, and spot on temp management. But I couldn't live with that tick. I felt like I was crossing a mine field every time I drove it.

Money is not that big of a deal (still can't afford a head though), but I'm still trying to save it.

I filled my cart at Summit Racing with everything I need and it came to around $380, free shipping. I have found cheaper gastet sets and cheaper rings sets at Rock Auto. But the rings where aren't Sealed Power, and the Gasket set isn't Fel-Pro. Any opinions on that?

And BTW: I absolutely love this thing despite our awkward first meeting. From underneath it is one beautiful vehicle (I read somewhere that they brought in an engineer from Porsche for chassis design on the WJ for better road feel), and it looks pretty good on top too. I forgot to mention on the first post that it came with brand new Tires too.

(edit I forgot to mention the broken piece is pretty big. I'll get a picture on here when I'm not lazy. But is there any chance of the thing rotating in there? Like if it were left in, what's the typical thing that would happen?

I also forgot to mention my eyes are going to be open wide for a used engine to COMPLETELY rebuild and have ready for when the Big Bang happens.

Last edited by 99Justin4.0; 10-04-2016 at 01:53 PM.
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Old 10-04-2016, 03:05 PM
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Geeeze... I'd be done if it weren't for these damn holders that go over bolts...
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Old 10-04-2016, 03:17 PM
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the felpro pan gasket looks pretty good since they include those plastic clips to help with installation. I picked up a cheap (non-felpro) pan gasket off of ebay and while attempting to install it last night I am sure my neighbors thought I was speaking in tongues given the language I was using. I was so frustrated.


if your going to cross hatch the cylinders would it not be easier to pull the head? without replacing the head the only cost would be in the gaskets.
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Old 10-04-2016, 05:30 PM
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Originally Posted by jon-d View Post
the felpro pan gasket looks pretty good since they include those plastic clips to help with installation. I picked up a cheap (non-felpro) pan gasket off of ebay and while attempting to install it last night I am sure my neighbors thought I was speaking in tongues given the language I was using. I was so frustrated.


if your going to cross hatch the cylinders would it not be easier to pull the head? without replacing the head the only cost would be in the gaskets.
Wait.....What? How is he going to pull the pistons without taking the head off? He has to cut the ring ridge anyhow to not risk breaking the new rings.

The easiest answer to keeping a gasket in place is to use sewing thread thru every bolt hole until it's on with every bolt started, then cut the thread.
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Old 10-04-2016, 09:04 PM
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Well, I already have the Fel-Pro Pan gasket. My question was regarding the "Head Gasket Set".

And the head is already ready to be pulled.

I just have those two end bolts holding up the exhaust manifolds. I've heard a lot of people leave the manifold connected to the down pipes and just push them aside. I know those bolts connecting them are a major pain in the ***. Should I get the exhaust manifolds completely out or just push them aside like most others. In all of your many differing opinions, what are the Pros, cons, and what not?

It kinda sucks that now I just have to wait for parts...

Last edited by 99Justin4.0; 10-04-2016 at 09:07 PM.
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Old 10-04-2016, 09:21 PM
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Dave I forgot about the ridge line. I was thinking the crank could be pulled from below and the pistons with it. Obviously I never have done that.

A way I got the gasket on was to silicone the front and back along the block side and a couple spots along the sides. Then use the bolts to hold it up until the silicone cures. Remove bolts, silicone the pan where needed, then button back up.
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Old 10-05-2016, 12:10 AM
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Any of you guys ever used the Speed-Pro Hypereutectic DurOshield Coated Pistons?

With 200,000 miles and just a honing out, standard size should still be good I'm thinking. I think I just need to make sure to get rings that will seat really good.

Anyone with knowledge on a good ring brand and/or materials that would best suit this application scenario? I gotta get the order done tomorrow. Earlier the better. So these are last second tips!

Thanks Guys!!!
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Old 10-05-2016, 12:16 AM
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Not today! Most engine don't have enough clearance to pull the pistons out the bottom, especially a 6 with 7 main bearings. Even IF you could, imagine getting them back in with new rings! I've done a lot of work on Chevy small blocks and I can't tell you how many hone stones I've ruined by hitting the main bearing supports. That usually happens when you get tired and don't watch your depth too closely.

Excuse me for a minute. I have a cat standing in front of my keyboard! I love her, but she's a nudge sometimes. 15 year-old female can't get enough attention.

I personally like Perfect Circle. Chrome first ring, plain 2nd ring with expander, 3 section oil ring. Just check your end gap. (She just knocked my cigarette lighter off the computer table into the trash can!) Standard size will be fine up to .010" over. That's what the expander does, makes them conform to worn bores. They are known as MAHLE Clevite now.

Last edited by dave1123; 10-05-2016 at 12:34 AM.
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