7120 Head on a 2001 engine?

I have just recently joined the cracked 0331 head club. I have a 2001 Xj with 85,000 miles. It sounds like I made it longer than most. I picked up a head a while back for next to nothing. Its a '95 I belive (7120 casting) and it has been cleaned and checked by a machine shop, so I am good to go there. I know it doesn't have the alignment dowels, and I have to plug the coolant temp sensor hole, and I will need to fab something to mount the coil rail, but other than these things, what do I need to do differently? Will it work with my cast exhaust manifolds and new intake? I am hoping to secure an extra set of manifolds and a new head so I an make a complete build and swap and limp the old engine to and from work for a couple of weeks. I dont have any sludge in the bottom end, but I noticed a tiny bit of coolant under the oil fill cap. Any info on this swap (7120 onto a 0331) would be very helpful. Thanks!

JONNYD said:

I have just recently joined the cracked 0331 head club. I have a 2001 Xj with 85,000 miles. It sounds like I made it longer than most. I picked up a head a while back for next to nothing. Its a '95 I belive (7120 casting) and it has been cleaned and checked by a machine shop, so I am good to go there. I know it doesn't have the alignment dowels, and I have to plug the coolant temp sensor hole, and I will need to fab something to mount the coil rail, but other than these things, what do I need to do differently? Will it work with my cast exhaust manifolds and new intake? I am hoping to secure an extra set of manifolds and a new head so I an make a complete build and swap and limp the old engine to and from work for a couple of weeks. I dont have any sludge in the bottom end, but I noticed a tiny bit of coolant under the oil fill cap. Any info on this swap (7120 onto a 0331) would be very helpful. Thanks!

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Well I can answer the manifold question. Your 2001 exhaust manifolds will bolt onto the 7120 but the ports on the 7120 head are bigger than the 0331's. If you run the '01's exhaust manifolds you will run the chance of an exhaust leak since the ports are smaller on the manifold than the head. Good news is, your 2001 intake will bolt right up and work swell. I would suggest getting a 91-99 intake though. Good luck!

99-01 is the same intake manifold, you're good with that. it's the smaller exhaust ports that may cause the issue. although, i believe the port size of the exhaust manifold is a tad larger than the 0331 head's exhaust port to begin with. you could probably clean up the ex. manifold pretty easily with a grinder for a perfect fit to the new head.

regarding the exhaust ports - i swapped an 0630 head for my cracked 0331. to handle the exhaust port issue while keeping my factory exhaust (two cast manifolds + two pre-cat + four O2 sensors), i made an adapter plate to keep it from leaking. http://www.naxja.org/forum/showthread.php?t=919384 if your interested. you'de have to find out if the 0630 and the 7120 exhaust ports are the same though.

-mike

ok, so it looks like i was wrong about the severity of the port mismatch. that plate sounds like a good idea. any pictures of it? i'm just curious how much of a mismatch it was.

any idea how hot the exhaust manifold gets on our 4.0 jeeps? :dunno:

that's a good question....um, damn hot? i can't believe i've never checked. i'm going to hit it with the raytek when i get home.

I picked up a cheap set of manifolds from a 2001 wrangler (same as the XJ's in 2001) and I am going to check out the port mis-match. I hear that the 7120 heads respond well to port work and flow the best out of all the years. I hope i can make it work. I will post pictures when I get the stuff...

Ten High said:

ok, so it looks like i was wrong about the severity of the port mismatch. that plate sounds like a good idea. any pictures of it? i'm just curious how much of a mismatch it was.

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i just finally posted a couple pics here:
http://www.naxja.org/forum/showthread.php?t=919384

you can't tell from those pics, but the port mismatch is enough that there are actually visible gaps not covered by the even the flange from the manifolds. with the 0630, there was no way to grind the manifolds to match. that is unless the manifold was built up with either a welded on piece or just tons of weld. i talked to lots of people about the welding the castings and basically came to the conclusion that it would just be way simpler and more reliable the sandwich in a plate. i was told that if i welded the castings that 1) there was a pretty good chance they would distort and need a secondary "re-facing" operation after and 2) they'de probably crack down the road.

Thanks for the info. I will probably just machine one at my work (I work at a machine shop. I was a bit curious why you chose aluminum (it is an aluminum plate, correct?) vs. steel. The aluminum plate will heat up and expand about 3x as much as the cast iron...but I guess in this case the intake is alum too, so it probably doesnt matter much. I assume you took the gasket from the new head, traced the ports on the aluminum, compared it to the 0331 gasket, and covered the difference with the cutouts. Good work, they look nice. For somebody without the means, these would be very helpful. WIth all the 0331's that are starting to crack, I bet you will be selling these things like hot cakes!

JONNYD said:

Thanks for the info. I will probably just machine one at my work (I work at a machine shop. I was a bit curious why you chose aluminum (it is an aluminum plate, correct?) vs. steel. The aluminum plate will heat up and expand about 3x as much as the cast iron...but I guess in this case the intake is alum too, so it probably doesnt matter much. I assume you took the gasket from the new head, traced the ports on the aluminum, compared it to the 0331 gasket, and covered the difference with the cutouts. Good work, they look nice. For somebody without the means, these would be very helpful. WIth all the 0331's that are starting to crack, I bet you will be selling these things like hot cakes!

Click to expand...

nope, mine's steel - i liked the lower thermal expansion and higher modulus of elasticity of steel. it'll deflect only about a third of what the same thickness AL would have (under the same pressure). plus - i wasn't overly concerned with the 2 lb weight of steel.

regarding how i traced the ports, i used both gaskets combined with both heads and my cast manifolds. i made a full size print and then traced that onto poster board to do trial fitting and stuff. I thought I'd be able to trace stuff and just have it work, but it turned into much more of an iterative process than i thought. much more time consuming than I had anticipated.
when you start tracing them out though, it'll help to pick one of the dowel pins to locate from. if you look at my plate, i made one of the dowel pin holes round and slotted the other.

i wish i had access to a shop when i was making mine. i had to make the print and then have a local sheet metal shop punch it for me. the last place i worked was smaller and WAY more relaxed - they let me on the machines anytime i wanted as long i wasn't keeping them from real work - not here though.

you sound like you're gonna be fine making your own - let me know if there's anything i could help you out with though.