4.2 in a Comanche

[matt89mj]

I realize this may sound like a dumb question but I am relatively new to the MJ/XJ thing so here goes. I have been looking around for a new engine for my MJ project and I got to thinking(this is usually bad) that I should be able to swap a 4.2 in there in place of the 2.5, right? I mean if a 4.0l swap would be easy why not a 4.2?

 

Anyone here done anything like this or have any input on this idea. Figure with the 4.2 and a 4.0l head with either Mopar MPI or the TBI kit that is made by Howell.

TIA,

Matt

[mj_lover]

4.0L and the 4.2l are very similar. 4.2L is carbed the 4.0L is mpfi or efi.

what are you looking for out of the engine? you mentioned you wanted fuel injection, then get the 4.0L.

of cource if your just looking for power, you could always stroke the 4.0L to a 4.6 or 4.8

gl, and feel free to post any questions.

[Bounty Hunter]

I mean if a 4.0l swap would be easy why not a 4.2?

Where'd you hear that a 4.0L swap is easy? You would likely need an entire front clip from an 4.0L XJ or MJ as I beleive their designed differently, allowing for a longer engine. Don't be surprised if you won't have enough clearance at the firewall as well. Motor mount perches will need to be cut off the psuedoframe and new ones welded on. Still sound easy?

 

The 4.0L and 4.2L are basically the same externally, so it's a toss-up. Just be sure to use the 4.0L head as it flows much better.

[matt89mj]

OK, easier than a cheby swap. Didn't realize that a 4.0l or 4.2l swap would be that involved. I had a feeling the motor mounts would have to be moved, but a new front clip. Holy crap, didn't think they were that much different. I guess the only way that would make a diff is if I wasn't putting a 97+ front end on it.

 

I knew that the 4.0l heads flow better, I plan on that in my CJ8. I guess the main reason I am looking into the 4.2 swap is because I think I will be able to get a free block with a 4.0l head. I would have to build the motor but the block is solid and ready to go. At least that is what the guy is telling me, I have not looked at it yet. That is why I posted here, to see if it would be worth the effort or not.

 

I know I want 6cyl power in the MJ, it is a truck and I plan on using as such. Don't get me wrong the 2.5 in my YJ is a strong runner, but on the street I wish I had more power like the XJ with the 4.0l.

 

Any advice in this is greatly apreciated. I really want to get started on this project. And this weekend will be the official start, I am going to rip the flares off and start on the body work. I am probably going to start taking the interior out of it too.

 

 

 

Thanks for the input so far,

Matt

[DirtyComanche]

The swap would be hardish. You'd need a decent vehicle for a donor as you need the crazy small radiator for the 4.0 and all the peices that make it mount. And you'd have to wire up the MPFI, which with a donor vehicle with harness would probably not be too bad, or a complete replacement harness. You'll need a new trans too. And your driveshafts will probably be the wrong lenght.

 

 

I don't think there's any differences in the rest of the shell. I never really compared my 4.0 to 2.5 as far as the firewall goes. If you run into any problems just keep a sawzall around and you'll be set.

 

 

Oh yeah, there'll be lots of vacuum harness stuff to deal with. I think I'd recommend getting a GDI 3-core radiator to start with and just getting the mounts out of a junkyard. Assumably if you go the 4.0 route you'd get the wiring for it and vacuum stuff. And the same would go for the 4.2...

 

 

Edit:

 

Just went out and looked at both of mine. Firewall looks the same, a hammer would solve any problems. The front would need lots of cutting and possibly bending up some sheet metal to make it all fit right. I think it's very do-able though.

[whowey]

You are getting some mixed info.

 

The 86 MJ would have the shorter front clip. The 2.5l and the 2.8l both are compared to the 4.0l a short motor. But after 87 until the end of production the MJ has the longer front sheet metal.

 

I will get the measurements from a later 2.5l(90), and compare that. But the front should be identical to the 4.0l fronts.

 

But having a complete donor vehicle makes the swap 10,000% eaiser.

The Cherokee and Comanche front harnesses are identical, as are the engine management systems. If you pick-up a 4.0l Cherokee the swap would be infinitely eaiser, than trying to get all the parts from different sources.

 

 

Now this is assuming, your screenname Matt89mj, comes from having a 89 MJ.

[matt89mj]

That is correct, this is all on an 89 MJ.

 

The only problem of picking up a donor vehicle is that I am running out of space for Jeeps and Jeep parts. :lol: I do have some other options, but would really like to put a 6 in this Jeep. At least knowing that the front clip is longer gives me hope that the sheet metal swap will work. After I get started on the body work I will take some time to take measurements from the MJ and compare them to the XJ's that my wife and I have. Then I will make the final decision, based on what I find.

 

It is times like this that I am kicking myself for selling that 2.5 that I had about 6 months ago. :roll:

 

 

Thanks again,

Matt

[mj_lover]

i put a 4.0l into my '88 which origionally had a 2.5L you need the new mounts, the ones that bolt onto the frame, and a new rad suport. i need to move my tranny x-member back. bur i whent from stick to auto, not sure if it makes a difference though. i can't coment on the wiring, as i never got the swap done, had to re-gut the whole damn truck because of a previous screw-up i thought i had fixed.

good luck mate, it is do-able, just takes alot of time and a fair chunk of cash

[DirtyComanche]

I didn't realize they changed the front according to year. It's something I never noticed before. Although, that makes more sense than according to engine type.

[Bounty Hunter]

For me, the GM 4.3L Vortec v6 or a SBC would be easier and more power. And it's not like every other 4.0L jeep out there (except with a more hacked up install job).

[Pete M]

Swapping another 2.5L is obviously the easiest way to go. The later model engines (TJ/XJ) are rated for more power (though that's probably due to the heads and intake rather than the block itself) and I've heard from a couple different sources that they swap right in using the accesories and brackets from your current engine. I haven't tried that myself though.

Keep in mind that the 4.0L and 2.5L do not share the same engine-to-trans bolt patter.

Another option for replacing the 2.5L is the Chevy 3.4L v6 because they do share bolt patterns and you might be able to keep your tranny. Check out the article I wrote on that:

http://autos.groups.yahoo.com/group/jeepcomanche/files/

It's the second one down. If you have the AW-4 auto, you might have to convert it to a manual shift due to the computer-controlled aspect.

Jeep on!

--Pete

[whowey]

I didn't realize they changed the front according to year. It's something I never noticed before. Although, that makes more sense than according to engine type.

 

 

Well, actually it was for engine type.

 

The chevy motor was dropped in 1987 in favor of the AMC 4.0l. The front clip was changed to accomodate that change

[matt89mj]

Thank you for all of the input. My only hitch with putting a Chevy motor in there is that I, for some reason, can't bring myself to do it. Don't know why, perhaps it is the CJ owner in me, but I just can't bring myself to put a Chevy under the hood. Just my opinion, not talking bad about doing it, I just don't want to go that route.

 

The 4 cyl is a good strong motor and yeah it would be the easiest swap, but I am looking at getting more power because it is going to be a partial DD once it is all together.

 

I must say tho that the write up about doing a 3.4 swap is very interesting and pretty cool reading. Didn't know that there were so many similarities.

 

The main reason that I was looking at a 4.2 is I like the 4.2. You can FI them or TBI them, put the 4.0l head on em. According to clifford performance the kit that they sell for the 4.2 that has a aluminum 4.0l head and a cam will give you close to 120 more horses. That doesn't include what you would gain from the FI or TBI upgrade.

 

I guess I am getting a little in over my head here. But I am going to look into what it will take and see what the best option is to put 6 cyl power in there. As of right now putting another 2.5 in is out, for now. Guess I am just looking at something unique, that no one else has around here. Then again a Comanche in stock form fits that bill. :lol:

 

Thanks again for the input,

Matt

[Bounty Hunter]

Guess I am just looking at something unique, that no one else has around here.

Then why look at any jeep I-6?

[matt89mj]

My only hitch with putting a Chevy motor in there is that I, for some reason, can't bring myself to do it.

 

That is why. Keep it Jeep, that is my way of thinking. A V8 would be too much for the trails from my experience, and just putting another 4 in there would make it a dog on the street. I already have one like that, my YJ, don't want another one. The 258 is one of those engines that you don't see on the road much anymore and they are good strong engines. With some good tweaking you can make em better than the 4.0l in stock form. I don't want the typical Chevy swap, absolutely refuse to even think about putting a Ford under the hood. The 4.2 isn't a common swap, and since the mounts are the same for the 4.2 as they are for the 4.0, it would be a fairly simple swap. That way I can put any trans after it, and any t-case. I would probably put the T5 that I have sitting in the shed with who knows what for a tcase(have not decided on that yet). They never put the 258 in the XJ/MJ chassis, they started with the 4.0l. So it would be different and a little unique. I was just hoping that someone on here would have some input as to what it would take to make it work.

That is all.

 

Thanks,

Matt

[whowey]

My only hitch with putting a Chevy motor in there is that I, for some reason, can't bring myself to do it.

 

That is why. Keep it Jeep, that is my way of thinking. A V8 would be too much for the trails from my experience, and just putting another 4 in there would make it a dog on the street. I already have one like that, my YJ, don't want another one. The 258 is one of those engines that you don't see on the road much anymore and they are good strong engines. With some good tweaking you can make em better than the 4.0l in stock form. I don't want the typical Chevy swap, absolutely refuse to even think about putting a Ford under the hood. The 4.2 isn't a common swap, and since the mounts are the same for the 4.2 as they are for the 4.0, it would be a fairly simple swap. That way I can put any trans after it, and any t-case. I would probably put the T5 that I have sitting in the shed with who knows what for a tcase(have not decided on that yet). They never put the 258 in the XJ/MJ chassis, they started with the 4.0l. So it would be different and a little unique. I was just hoping that someone on here would have some input as to what it would take to make it work.

That is all.

 

Thanks,

Matt

 

The 2.8l was a Chevy motor. Second finally got around to measuring the engine-bays. A 4.0l and a renix-era 2.5l are exactly the same size, no difference anywhere.

[matt89mj]

Yes very true, but we all know how long they lasted. :-D

 

It would be different for me if the Jeep already had a 2.8 and then I would probably just put a 4.3 or a 3.4 in there, but it didn't so I really don't want to. That is why I am looking in this direction.

 

 

Thanks for the measurement information.

 

Matt