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Swapping a 4.0L Into a CJ-7

Trenton McGeeWriterTrenton McGeePhotographer

It seems like everyone and their brother has put a small-block V-8 into a CJ-5 or CJ-7, and those that haven’t done it have heard about someone doing it. We’ve covered swaps like these many times. There are a lot of benefits to putting a V-8 in a CJ, but it’s not the only viable swap out there. Few people will fault the durability and reliability of a Jeep’s own 4.0L, and long-nose CJs were designed to accommodate the 4.0L’s predecessor, the 4.2L, right from the factory. In fact, the inline sixes share the same block and external dimensions, which means lots of stuff can be swapped between the two engines (accessory drives, engine mounts, and so on). On paper, swapping a 4.0L into a CJ is a piece of cake, yet somehow we’ve never covered one in these pages until now.

We decided to find out if a 4.0L swap is as easy as it seems, so we plugged a 4.0L scavenged from a ’96 Jeep Grand Cherokee into our ’84 CJ-7. Our CJ was equipped with a pathetic high-mileage four-banger that couldn’t maintain 65 mph going downhill with a tailwind. Because it seemed so easy, we even had grandiose visions of getting it done over a three-day weekend. That didn’t happen, but we did complete the swap in about two weeks, working on it in the evenings and over a couple of weekends in between our real job. We also did it without ever picking up a welder or making any custom modifications, so it’s a fairly easy bolt-in that doesn’t require any fabrication skills. What follows are the highlights of what we did and some of the problems we ran across, so you can decide for yourself if it’s worth the work. As with any engine swap, there are pros and cons, but in the end, we did end up with a very reliable, torquey CJ-7 and no longer had to live in fear of maintaining freeway speeds.