Newbie CJ Owner with 4.2L/4.0L Concern

Hoping an easy answer is at hand. Bought an 84 CJ7 with a blown engine. Has a 4.2L (IL6 Cherokee) w/ 4.0L head and auto trans. Wondering if the 4.0L block (IL6) is an easy/good replacement. All thoughts welcome.

 

4.2 was a pretty solid engine although not built for high performance. 4.0 is a good engine with great power output and torque for it's displacement in it's stock fuel injected form.
Do you still have the 4.2 intake and carb on the 4.0 heads? If so, I'd just put a 4.2 short block in it since you won't have any major performance gains without changing everything to 4.0 efi which is a lot more involved (ecm, wiring harness, fuel pump, sensors, etc).
The 4.0 block will work, but you'll probably have to buy a transmission adapter kit like the one at https://www.4wd.com/p/advance-adapt...n-aluminum-bellhousing-712569/_/R-BDFD-712569 to mount up to the CJ transmission (I don't know what model your transmission is or what other modifications the previous owner did).
If you just want to get it back on the road, a rebuilt 4.2 short block would be the least expensive and easiest to way to go. If you're looking for more power, the possibilities are only bound by the limits of your credit card.
Keep everyone posted on the changes and I'm looking forward to seeing some pictures of the CJ's progress.

 

Here are a couple of photos of the engine. I understand the full 4.0epi was installed along with the 4.0 head on the 4.2 Cherokee block. I*'not sure why the Mopar sticker reflects a 4.2 MPI kit when its installed on a 4.0 head.

 

Intake has been converted to fuel injection which is a huge plus. 4.0 heads with 4.2 intake converted to efi 4.2 or 4.0 block will work well but unless the heads were modified for the 4.2, the ports will line up like they're supposed to on the 4.0.. You've already got the higher pressure fuel pump. Make sure you can buy the bell housing adapter for the 4.0 to your transmission model if you go that route..
If you want real power gains, you can do a 4.0 block with a 4.2 crankshaft = 4.6 stroker..

 

Thank you Groundfault. Very helpful. Now I'm looking for a reman 4.0L (1991-95) long block or at least a very reliable source for a used long block. Any ideas?

 

Never personally bought a reman engine before. Check reviews and warranties online.
I'd check Craig's List for a used engine. Usually can find Jeeps being parted out and most of the salvage yards post ads.

 

what part of the country are you in??

 

That adapter is for a manual transmission, you have an automatic, it will not work.

The bolt pattern for the AMC 258 and Mopar 4.0 are the same, as are the AMC V-8 engines, read the information on that adapter, it fits 258, 4.0, 304, 360, etc.

I just put a 4.0 (bored & stroked to 284 CI) in my 1985 CJ-7 with the TF-999 automatic, same as yours, and it bolted right in, everything is the same with the exception of one motor mount bolt, that had to be drilled on the MM, to accept the larger diameter bolt that the 4.0 engine block uses.

Having clearing up that issue, you can bolt a 4.0 engine to the transmission that is in your CJ-7, but your TF-999 automatic transmission does not have the provision to mount a CPS sensor, unless someone modified it. That’s what I did to mine, I cut a hole and fabricated a mount for a CPS sensor. Your current 4.0 fuel injected head conversion should already have a CPS sensor, so I you should be GTG.

Does your engine have a CPS installed? Look at the front of your engine, and see if there is a CPS sensor adjacent to the harmonic balancer, or maybe one was installed in the OEM location for the 91-95 4.0’s, which is on the upper drivers side of the bell housing of the transmission. It can be viewed easily after opening the hood, and looking for it on the upper transmission bell, on the drivers side.

The Mopar sticker reads “4.2” because it is designed for the 258 (4.2) engine. Placing the 4.0 head on the 258 (4.2) engine does not change the CID, it is still a 258 (4.2).

Thats a nice looking kit you have on your engine, it looks like the OEM 4.0 engine.

 

Yeah, what part of the country?

Welcome from Florida btw!

 

Welcome from north central West Virginia