motor swap precautions

[Whynotcj7]

My brother an I are about to attempt a motor swap and I wanted to know if anyone has any words of wisdom or problems we may encounter before we start. We will be taking out the 4 banger in my '84 CJ7 and dropping in a 6 banger from a '87 CJ7. Can I get some reassurance that its just going to drop right in? Motor mounts fit right in? Thanks for all the input guys, I appreciate it.

 

[69jeepcj]

I thought I had heard this wasn;t the simplest swap, so I did some looking and this is what I found.

RE: This is what I had to do when I swapped out the 2.5 for a 4.2 (Kept the T5 manual) :
I first had to locate a bell housing from a 6cyl CJ that would work with my T5. Luckily, being as the 4.2/T5 was an option, that wasn't difficult. The 2.5 and the 4.2 do not share the same engine bolt pattern, so this is required.

Next I had to swap out the 10 spline input shaft with a 14 spline on the T5 to correspond with the 4.2 flywheel clutch assembly.

The 4.2 sits back further in the engine compartment then the 4cyl, so the whole drivetrain moves back about 2 inches. This requires shortening and lengthening the drivelines and moving the transmission crossmember back to the next set of holes in the frame.

You will need a 6 cylinder radiator, and if you use a "newer year" 4.2 with a clutchfan, you must use a radiator with the off-centered cap. The older CJ's used a radiator with a centered cap that was deeper and it will interfere with the fan. Be sure to use a shroud also.

You can re-use the stock ignition control module...not sure about ECM as I de-smogged mine prior to a swap and none of it was functional anymore.

 

[Whynotcj7]

Thanks 69jeepcj, do you think I would have to swap the spline even if i have the transmission that came with the motor? I took the motor, transmission, radiator, the computer, starter, fan and shrod. Will i have to drill new holes on the frame, move the motor mounts ? I'm not too excited about shortening or lengthening the drive shaft either because we've never attempt to yet. The compression test is good, but are there any gaskets or parts that I should replace before I drop it in ? Man, I'm excited to swap but worried too

 

[69jeepcj]

I dont have any experience with this swap personaly. The info I put up is what I found doing a google search because I had heard it was not a straight forward swap. The problem I see with this swap is you have a cj and are putting in a yj engine, trans. The cj never came with the trans or tcase that the wrangler uses, and the output shafts of the wrangler tcase is on the wrong side, so you cant use it, and you will probably need a adapter for your current 300 tcase to bolt to the wrangler trany, the adapter kit will probably have a new mainshaft that will need changed on the trany. It would be simpler it find a cj engine and trans for your swap. The reason is you will not have as many complications. If you use the wrangler engine there is computers, tcase adapters, probably wiring harnesses because your new engine will be computer controled and the cj is not. If you get a cj 258 and trans the only major things to change will be motor mounts and moving the crossmember back, and the driveshafts. you will be able to use your current tcase without an adapter which will save big bucks.
If there are no hole, You may have to drill new holes in the frame for the crossmember either way you go, but thats not a biggie. I would change the water and oil pump before intalling the new engine. For the driveshafts, if you have a 4x4 shop close by, check with them to see if they have used 6cyl driveshafts and give them the measurements from the tcase yoke to the rearend yoke. Thats where I have gotten mine in the past.