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4.2L in an XJ?

M

MSS

Registered User
Location
Syracuse, UT
Background - I have an XJ with a tired 4.0L (305,000 miles) and I am looking for replacement options. I also have access to a freshly rebuilt 4.2L from a CJ. So is it possible to put the 4.2L in my cherokee?

I am thinking about using it basically as a short block for my 4.0. I have read a bunch of articles about putting the 4.0L head onto the 4.2L. This seems to be basically a bolt on. So, if I can put the 4.0L head, intake, exhaust onto the 4.2L that should take care of the majority of my fuel injection swap - am I forgetting anything?

The part I am worried about is the transmission. I would like to retain the 231 and relative location. I am guessing that the motors have different bell housing bolt patterns (it just couldn't be that easy). I currently have an AW4(auto) and I haven't seen much adapter support. I also have access to an AX-15 and wouldn't mind converting - would this work? It seems to me that the '89-ish wranglers (with the 4.2) also had an AX-15.

So, basically, I'm looking for support from anyone who has attempted something like this. Is this even possible and what I am forgetting about?
 
Badger

Badger

I am the Brute squad
Location
South Salt Lake
why would you want to back track by putting a 4.2 into a vehicle that has a 4.0 .....you said it yourself plenty of articles for going from 4.2 to 4.0 there is a reason behind this.

the bolt pattern should be the same for the bell housing.

now if i were you i would stroke the 4.0
 
M

MSS

Registered User
Location
Syracuse, UT
Main reason for swap - dying 4.0L vs. fresh and healthy 4.2L. Rebuild and stroker kit for the 4.0L would be sweet... if I had the funding. I am just looking for a cheaper alternative.

The swap would be a fresh 4.2L block (and guts), fresh 4.0L head, and all the cherokee fuel injection (at least that is what I hope).

Same bolt pattern - so an AW4 should mate up to a 4.0L? Anything I am forgetting?
 
Badger

Badger

I am the Brute squad
Location
South Salt Lake
nobody goes that route and there is a reason behind it.as to why i can't remember off the top of my head.

as for a stroker kit ....if you have a 4.2 that is fresh you have a stroker kit sitting there.if you dump the 4.2 crank and connection rods over to the 4.0 block you have a stroker.the only thing that would be left would be to adjust the fuel ratio with an adjustable map sensor and bigger injectors
 
Darwin

Darwin

GREASE MONKEY
Location
sandy
your tranny will bolt to the block no problem. you might have trouble with a flex plate though since they are specific to each motor. you should check out clifford performance for answers to all your questions. the swap sounds like it should be pretty easy from what i've read about it.
 
aerocorey

aerocorey

Blah
Location
Hill AFB
I seem to remember that there's an alignment stud or something like that that doesn't match up when putting a 4.0L head on a 4.2L block, but I recall that there's a simple machining solution to it. Also be aware that there's a difference between the 4.0L head and the 4.0L HO head when getting your parts. I'm sure you can work it out. As far as bell housing patterns it's been the same pattern for AMC 4 cylinders, 6 cylinders, and V-8s since the early 70s. It's the same today in Wranglers I believe. You'll have no trouble there. Motor mounts should be the same as well. Clifford is a good source of info, so is www.novak-adapt.com. They are up in Logan. Also check out www.jeeptech.com. Good luck.
 
M

MSS

Registered User
Location
Syracuse, UT
Thanks for the responses on this - I have been checking a bunch of other web sites as well and this definently seems do-able. So with that in mind I am going for it - If anyone remembers an issue post up.

Thanks
 
gijohn40

gijohn40

too poor to wheel... :(
Location
Layton, Utah
need help?

I am very interested in this swap due to my 4.2 is getting on in years as well.. so if you need any help on this give me a call or email and I can come help you out... this way I see what is involved and what to look for when I do mine...

John
 
M

MSS

Registered User
Location
Syracuse, UT
Why do you see this as a downgrade? - honestly just trying to understand. When the swap is done I will basically only be using the 4.2L block (and guts). It will have a 4.0L head, 4.0L intake/exhaust, and the same fuel injection/control system. To me, it seems that I will basically be increasing my displacement.
 
AINT SKEERED

AINT SKEERED

Balls to the Walls
Location
Salt Lake
MSS said:
Why do you see this as a downgrade? - honestly just trying to understand. When the swap is done I will basically only be using the 4.2L block (and guts). It will have a 4.0L head, 4.0L intake/exhaust, and the same fuel injection/control system. To me, it seems that I will basically be increasing my displacement.
Click to expand...

Well stock output for the 4.2 is less than half. Your mileage will most likely go down. You would not legally pass emissions(older motor).

Taking the crank, connecting rods, and rod bearings and putting them in your 4.0 block will give a 4.5 stroker, lots of displacement gain with no out of pocket money(Possible machine work). At that point you would need new rings, which are dirt cheap, and you would have a very strong motor.
 
J

jeepdude89

Registered User
Location
Logan
if your still doing the swap and putting the 4.0 head on the 4.2 there is a little machining that you have to do to get the head on.. um i think that the bolt holes have to be drilled larger or something of that sort. i know this cuz i was thinking of putting the 4.0 head on my cj engine but then decided to buy a 4.0 and make a 4.7 stroker
 
1993yj

1993yj

.
Location
Salt Lake
I like AINT SKEERED's thinking here. I am also assuming that if you Cherokee has that many miles on it then it must be a daily driver. If that is the case you can't legally put an older motor in any car and have it pass. If you were just using it on trails and registering it as OHV, then do whatever, but for DD, stick with the original block. I personally think this route will be easier anyhow.
 
B

bobdog

4x4 Addict!
Location
Sandy
With the 4.0 head and induction/exhaust on the 4.2 I really dont think any inspector will ever notice. Remember the 4.0 is basically a 258 with a few refinments. To the casual eye the swap will look factory. 258 owners have done this many times, it is not a new idea and it is proven to work. What is the big deal.
 
1993yj

1993yj

.
Location
Salt Lake
bobdog said:
With the 4.0 head and induction/exhaust on the 4.2 I really dont think any inspector will ever notice. Remember the 4.0 is basically a 258 with a few refinments. To the casual eye the swap will look factory. 258 owners have done this many times, it is not a new idea and it is proven to work. What is the big deal.
Click to expand...

Just trying to help avoid any hassels in the future.
 
M

MSS

Registered User
Location
Syracuse, UT
Well, I still think I am going for it. What do I have to loose, other than a weekends worth of freezing in the garage... As far as the emmissions visual inspection goes, I agree with bobdog. I would be really inpressed if someone could tell the age of the metal in the block by looking at the outside. Physically, the blocks look almost identical to me.

I'll try to take some pics and let everyone know how it went.
 
M

MSS

Registered User
Location
Syracuse, UT
Just thought I'd give a quick update. Got the engine in - runs great. The build went suprisingly easy. Almost everything bolted right up. If anyone is interested (let me know) I can put together something that shows all the weird stuff. It seems to have good power (not much to compare too as the engine was dead when I got it); specially bottom end. It has no problem smoking the 31's. Plus it looks totally stock. For anyone that was interested, it passed emmisions/inspection without any issue.
 
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