1994 ZJ bought for my brother / Piston compatibility?

Trigg

Member
Long story short. My brother turned 17 and I found him a 94 ZJ for $500. Absolutely Zero rust and Interior is a solid 8/10. PO originally said he bought it drove it home and let it set. It needed the tank dropped cause of bad gas. Well upon looking at the jeep I did my normal compression test the motor, verified spark and fuel. During that I got a whiff of the fuel and it was indeed getting stale. But it fired up and sputtered for a few seconds and died. I gave the man 500 cold ones and had the car towed to the house.

Fast forward. New gas filter and gas. Fires right up. Now I have a 02 TJ as a offroad daily. So I am highly aware of the 4.0 sounds. This ZJ sounded like a bad case of lifters and valve clatter. Checked, cleaned, soaked lifters, and re-torqued rockers. Not the problem. Now granted my hearing is really not the best but, It sounded more like Piston Slap or Rod Knock to my old man. Should have listened lol. But anyhow, played the which injectors kills the knock and its number 1 piston. Sent bore scope in from top and seen a nice piston skirt wear mark. Pulled the oil pan. Not a single flake but Number 1 bearing wasnt toast but it wasnt good.

Jeep has 230k miles but I swear the motor doesnt even have 10k on it. Hardly and grim and gaskets just look fresh. Im suspecting a a rebuild at some point and not a reman. I say that because the connecting and main bearings are Sealed Power. Not saying they couldnt have used them I just never have seen them used in a reman.

I've already tore the motor apart and its pretty dagum clean in there.

So to my questions

To me P1 bearing looked somewhat starved of oil. Oil press was good and had the proper amount of oil. This motor seems to be tilted towards the rear is this normal and is P1 starvation a issue?

Rebuilder didnt use Moly Skirt Pistons. I can see why Cant find any for a 94. Is there any known differences between the 96+ pistons? cause I can find them for days.

Thanks for the help gents, Ill throw some pictures up of the jeep and the motor later.
 

Strodinator

Caught the Bug
There should be zero differences in the internal part of that engine. From 87 to 06 most of it remained the same. As long as the bore is the same, which it is, and the Pistons are the same, which I'm pretty damn sure they are, then the rings are interchangeable

Sent from my PH-1 using WAYALIFE mobile app
 

Strodinator

Caught the Bug
There should be zero differences in the internal part of that engine. From 87 to 06 most of it remained the same. As long as the bore is the same, which it is, and the Pistons are the same, which I'm pretty damn sure they are, then the rings are interchangeable

Sent from my PH-1 using WAYALIFE mobile app
And a slight lean to the back is normal. Hence the rear sump pan. It also helps to align the transmission and transfer case with rear pinion.

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Trigg

Member
I appreciate the info. I figured there wasn’t a difference but never hurts to make sure. Thank you.
 

Trigg

Member
For anyone searching the only true difference for the pistons is the Compression Height distance.

The only years I have verified are 90-95 which are 1.585 CH and 96-02 1.592 CH which equates to (.007) 7/1000 difference.

Im going to mic and check clearances to see if the .007 will have any effect but ill do the math and post back with the numbers of what I find.
 
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