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Cracked head, blown gasket, head swap questions

xjtrailrider

NAXJA Forum User
NAXJA Member
Location
Roanoke VA
Okay, its been years since I put a head on any of my XJ's so my memory is rusty.

The Jeep; 1989 MJ with a 1998 4.0, still running RENIX on it. Still running the RENIX intake/exhaust. The head is cracked or the head gasket is blown.

I have a 1994 head on a used engine that I'm going to swap over. Not enough time to do a proper head/valve job to it, my son needs his truck back for work. I know the head is good as the engine just came out of my 94 XJ, the block needs work (rings) but it ran good otherwise.

Any fore seen issues? Anything I need besides a FelPro head gasket kit?

Are the head bolts "torque to yield"?
 
Anytime the head comes off it should be taken to a machine shop so they can mill it flat. These long straight six heads tend to warp. The head bolts have a 4 stage torque to them and are set with a final torque spec of 110 ft-lbs except the front drivers side which goes through a coolant passage. That one gets thread sealant and final torque is 100 ft-lbs. Its a good idea to replace the head bolts but the FSM says you can re-use them once.
 
Yes, bolts are TTY. Can be re-used once, but I would buy a set of head bolts.
I would get access to a straight edge to confirm the good head is straight. Should really go to a shop to check it.
For what it's worth, when I had my friend replace HG I didn't do anything with my head and my heep is fine. Use the renix int/ex gasket with the renix intake/exhaust mani.
 
Thanks, I thought about getting our calibrated straight edge from work and check the surface. This is going to be a nascar pit stop of a head replacement though.

I did look at a new head from Oriellys, they want $379. Seems high, I can get mine reworked for $200 but he is a week behind right now. No time for that.
 
The 98 will be different casting number than the 94 as I understand it the only difference is the temp sensor port at the back of the head (some have it ported some don't). As long as that doesn't hold you back it should be simple.

It's good advice to get the parts surfaced and checked but I've seen done without it. I'd make sure to follow the removal bolt pattern if there is one (some aluminum head have to be loosened in the correct pattern to avoid warping) , it's s risk but I think it can work out, certainly in the sort term.

Do you use the lifters and rods from the 94 ? Or do they need to match the wear on the 98 cam?
Forget how that is supposed to be.
 
The 98 will be different casting number than the 94 as I understand it the only difference is the temp sensor port at the back of the head (some have it ported some don't). As long as that doesn't hold you back it should be simple.

It's good advice to get the parts surfaced and checked but I've seen done without it. I'd make sure to follow the removal bolt pattern if there is one (some aluminum head have to be loosened in the correct pattern to avoid warping) , it's s risk but I think it can work out, certainly in the sort term.

Do you use the lifters and rods from the 94 ? Or do they need to match the wear on the 98 cam?
Forget how that is supposed to be.

The 98 4.0 that is in there now has the temp gauge sending unit at the back of the head, so does the 94 head. I believe both heads are 0630 castings. I will use the push rods, lifters, fulcrums from the 98 engine. Basically just swap the head.

Neither head is aluminum.

EDIT: I see that my 94 head is a 7120 casting, the 98 is a 0630 casting. I think the 98 head has cracked into an exhaust port. no oil in the coolant, or coolant in the oil. It just steams out the exhaust.
 
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Anytime the head comes off it should be taken to a machine shop so they can mill it flat. These long straight six heads tend to warp. The head bolts have a 4 stage torque to them and are set with a final torque spec of 110 ft-lbs except the front drivers side which goes through a coolant passage. That one gets thread sealant and final torque is 100 ft-lbs. Its a good idea to replace the head bolts but the FSM says you can re-use them once.

What sealant is recommended for the threads on that head bolt?
 
What sealant is recommended for the threads on that head bolt?

pipe dope is fine. I like the blue stuff. ARP makes good thread sealant, with a higher temp rating than the normal stuff.

Do not reuse the bolts. I know, I know, I know, it says re use them once!!!!! but why bother? Why risk it? I've read many many many engineering articles on the topic of bolts. There is a shitload of science here. Seriously, if you want to have a good set....there expensive, but stud it. (you can reuse these...)

ARP 146-4201 maybe...double check me on that number. The last set I bought from summit maybe, it was like 150 bucks.
 
Question, will the 7120 head work with the 98 block and how well will it play with the RENIX intake/exhaust?

I have had issues with the 0630 head and exhaust leaks at the manifold gasket.
 
The 98 4.0 that is in there now has the temp gauge sending unit at the back of the head, so does the 94 head. I believe both heads are 0630 castings. I will use the push rods, lifters, fulcrums from the 98 engine. Basically just swap the head.

Neither head is aluminum.

EDIT: I see that my 94 head is a 7120 casting, the 98 is a 0630 casting. I think the 98 head has cracked into an exhaust port. no oil in the coolant, or coolant in the oil. It just steams out the exhaust.

I've done this job and help do cylinder head swaps on much more sensitive motors with aluminum heads, those had to be loosened in order, the cast iron I don't think I've seen a order for bolt removal but I've not looked at the 4.0 requirements.

BTW those head swaps with donors from good motors done without machining worked fine (kids with no money working on our own cars). as long as the cylinder head in not warped you should be good to go.
 
I've done this job and help do cylinder head swaps on much more sensitive motors with aluminum heads, those had to be loosened in order, the cast iron I don't think I've seen a order for bolt removal but I've not looked at the 4.0 requirements.

BTW those head swaps with donors from good motors done without machining worked fine (kids with no money working on our own cars). as long as the cylinder head in not warped you should be good to go.

That's what I'm thinking. My donor motor has never over-heated. I have owned the motor since almost new. I'm tempted to just check it for flatness and drop it on.
 
I've done just that on both my 2000 XJ (dropped a 93 head on it 110k kms ago) and my 1988 MJ (it got a 92 head) about 13k kms ago.
Both motors are doing just fine without machining and such.
 
Being a member here for a long time and spending hours searching stuff, I always like to update my posts.

I ended up using the 7120 head from my 94 motor. I checked it for flatness and it was good so its on the truck now. The 89 MJ with 98 block and 94 head, has never ran better!!

One note about the 98 block v the 98 head: The 98 block has dowels on each corner of the deck next to the oil drains/lifter areas. The 94 7120 head did not have holes for the dowels. Instead there is nothing there in the 7120 head, just empty space but clearance is tight. I decided to use my die grinder and open a small notch in the head where the dowels would be seated to make sure there wasn't any clearence issues that would cause the head to shift and the head bolts not line up. This worked just fine and took about 5 minutes to do. I used FelPro head bolts($30 at Oriellys) torqued in the ABC sequence of 25#, 45#, 110# and 100# on the head bolt that needs sealant.

I think I will drop the 0630 head off at the machine shop and get it reworked as I do not see any visual cracks. What I did find is that the head gasket was blown between the water jacket at #6 cylinder and the cylinder and water was pouring in. No damage was done to the motor itself. It won't hurt to have a spare sitting around!

I also found my exhaust leak, it turned out to be that the manifold was cracked in a place I couldn't visually see it.

All in all I spent $600 which included a new radiator, exhaust manifold and gaskets. I had about 6 hours in the job.
 
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Nice. Glad it worked like it should.
It's one of those gut check jobs, if you've got the feel for it and know you can do it, go for it .




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I thought the renix/7120 ports didn't line up o_O
 
I thought the renix/7120 ports didn't line up o_O

I'm pretty sure it's drag and drop so to speak. Seen plenty of non ho Renix engines with a 7120 head. I don't think they changed the exhaust when they drop it in.

I believe the 2000 -0331 heads are incompatible with the 87-99 exhaust manifolds.

My 89 MJ has a 98 XJ block, a 94 XJ head, A/C from a 96 XJ, a 96 XJ 8.25 rear and so on. It's a mutt.

But the 7120 head fit the 98 block just fine and the RENIX intake/exhaust fit perfect also

It runs and drives like it was all meant to go together
 
I have a renix computer a 93 block, 99 intake, 91+ header.
The only reason I went to a 93 block was the machine shop had one .30 over already for my stroker.

I could of sworn someone said the ports were off while I was doing my build maybe it was just because of the dowels.
Good to know though so I don't pass on misinformation.
 
The dowels are actually in the head, the block is supposed to just have the holes to receive them, in any event they aren't in super tight.
When I dropped the 93 head on my 00 block I simply used a couple head bolts with the tops cut off for alignment. Did the same when I dropped the 92 head on my 88 block.
Both motor years used the same Fel-Pro head gasket.
The exhaust ports on the 0331 (00+) are very different than the earlier 87-99 heads, large gaps.
The intake port positions differ on the 87-90 (sit lower on the head) , but are the same 91 up.


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