YJ 4.2 into a CJ7

[Thunder81]

Hello
Guess I'm new here so I'll tell you a bit about myself before I ask my question.
Heh where to start...
I'm pretty new to jeeps I guess. My 4x4 experience is mostly gravel roads with a bit of mud bogging and winter driving. I'm 29 and have bought my first real Jeep that being an 84 CJ7 . The body is in awesome shape for being 27+ years old. Oh yeah, I live in Alberta Canada...

So my question is
The current engine in my CJ is the stock AMC 258 i6 / 4.2l but it's in pretty rough shape. I found a good deal on a low milage AMC 258 i6 / 4.2l but its from a YJ.
I've been searching all morning and know that a CJ4 .2 will fit in a YJ but will a YJ AMC 258 i6 / 4.2l go into a CJ no problem?

Thanks
Ken

 

[Cheepjeep85]

Yeah they are the same motor, with maybe a few very minor changes but it will fit with little to no problems. The only minor changes might be in the emissions, and fuel delivery. But you can use all of your cj stuff on the motor to be sure everything is right.

Sent from my DROID2

 

[Petescj]

Cheepjeep is right. This was just Chrysler running out the inventory of 4.2s they had. There may be some slight differences in bracketry but you have everything you should need right there in your own engine bay.

 

[CJim7]

Depending on what year, that engine could be a serpentine belt settup. I swapped an '88 YJ AMC 258 i6 / 4.2l into my '84 CJ and discovered that most of the earlier AMC 258 i6 / 4.2l 's are V-belt set up.

Just wanted you to be aware. Make sure you get all the accesories from the YJ engine...It's hard to mix and match V-belt and serp pully parts. I found that out the hard way, it was a nightmare trying to locate all the proper pulleys.

 

[Cheepjeep85]

Or you can keep all of the stuff off of your motor when you do the swap, and you wont have to worry about that. Maybe even use your water pump

Sent from my DROID2

 

[Thunder81]

Thanks for all the input guys. Going to pick it up this weekend. He tells me he got the motor from Dodge and its got about 40 thousand miles on it. He wasnt sure if it was a new block but I think it was probably a reman. Also told me that it'll come complete with all brackets and accessories which is cool. Only think think I'll need to swap is the flywheel.

Anyways since I'm going to have the engine out and on a stand I plan to do a few things with it. Going to put in a mild cam, a 4.0 head, see if I can't find a mc2100 carb and a high flow oil pump while Im in there...

No point in replacing something without doing a few upgrades eh

Thanks again

 

[Petescj]

You are sure that this Yj motor is the AMC 258 i6 / 4.2l and not the 4.0 correct? Just checking before you go grab it. 4.0 will be fuel inj. Did you see it yet?

 

[Thunder81]

Pretty sure. I'm going to take a look at it tonight. Think it's an 89YJ so it should be the AMC 258 i6 / 4.2l . Plus he says its carb'd so... I'm not entirely sure but I dont think the 4.0's came with carbs

 

[Petescj]

Carb'd definately a AMC 258 i6 / 4.2l . Just checking.

Pretty sure. I'm going to take a look at it tonight. Think it's an 89YJ so it should be the AMC 258 i6 / 4.2l . Plus he says its carb'd so... I'm not entirely sure but I dont think the 4.0's came with carbs

 

[Thunder81]

Just looking for some advice
I've got the new to me motor and was just wondering what you guys would do to it since the motor is already out.
As I said before my plans include a 4.0 HO head, and a carb upgrade. I don't think I'll touch the cam shaft and I cant really afford to get much machine work done. Other then new gaskets and seals is there anything you guys would recomend I do to the engine while I've got it on a stand. I hope to get another couple of months out of my engine thats in the jeep... even that may be pushing it so time is a bit of an issue...
Thanks

 

[Cheepjeep85]

if the motor only has about 40k on it pulling the cam and reinstalling a new one shouldn't cost you anymore than the cam kit itself, the cam bearings should still have plenty of life left in em. now is the time to do it if you are going to have the head off. other than that continue with your plans, head, and carb. you mentioned new seals, make sure you go ahead and put a new rear main in while you have it on the engine stand, it wouldn't hurt to put a new timing cover gasket and seal in, and of course oil pan gasket.

 

[Thunder81]

I was thinking about doing the cam but from what I've read about the 4.0 head swap they don't recomend messing with the cam as it makes it harder to tune... Now that I think about that it doesnt make a whole lot of sense since I don't plan on going to efi... Hmmm I may have to rethink my plans... I still havent had a chance to pull it down and take a look at the internals... I suppose that'll tell me where to start.
Thanks for the reply

 

[Cheepjeep85]

yep that would be the first step, getting into it and knowing exactly what you have. a different cam won't make it any harder to tune than a factory cam. you only really have cam incompatibility problems with efi.