258?

[Junior]

So I'm going to pull the AMC 304 out of my CJ5 to fix an oil leak. Around the same time, I found a running AMC 258 i6 / 4.2l for cheap. From what I hear the AMC 258 i6 / 4.2l is evey bit as good as the V8 and even better in some cases.
So here's the question: How difficult is this swap? I imagine that the engine mounts will have to be relocated, but what else do I have to watch for?

 

[mylittlecj5]

thats a very uncommon swap (I sure wouldn't do it myself...). but the exhaust will be different, simple wiring changes made, a few other things I can't think of right now...

The AMC 258 i6 / 4.2l is a good low revving torque engine, but for what I do, its not enough.

 

[elwood blues]

x2 on the uncommon swap. I don't think I've ever heard of someone replacing their AMC 304 w/ a AMC 258 i6 / 4.2l .

Motor mounts will be different. Depends on your tranny as to weather or not it will bolt right up or not. From what I understand the wiring isn't too very different, and may not require a ton of changes. It really does depend on what year the AMC 258 i6 / 4.2l is coming out of though.

mylittlecj5 hit it on the head, the AMC 258 i6 / 4.2l is a good low revving torquer. As far as I know there's no real gain in gas milage one way or the other. I guess it all comes down to what are you doing with your CJ?

 

[Petescj]

What oil leak are you fixing that requires the motor to be pulled? If its only an oil leak why replace the motor , just fix leak and reinstall?

If you insist on another motor Id hunt around a bit for a 360 from a fullsize J-truck or wagoneer. Alot of times ( atleast around here ) they can be found just as cheap as a AMC 258 i6 / 4.2l . Belive it or not the 360 will get just as good of gas mileage and be a direct bolt in with no modifications required

 

[coldwater]

Depending on what you actually DO with your Jeep will depend on wether the swap will be a good one for you. Unless you are running around in the mud with your foot glued to the mat everywhere you go, you don't need a V-8 engine. I cut a AMC 304 out of the last Jeep I built to install the AMC 258 i6 / 4.2l , but then again, I am a big fan of that engine from way back. I have no idea why so many people seem to dislike them, maybe just be the "V-8 mentality" I guess...In stock form it will build more torque lower down than the AMC 304 , pound for pound It's tougher, more reliable, and will take a harder beating without complaints. Their easy to work on, easy to find parts for, and when I checked my last fill, I got an average of 26 MPG on an unimproved engine of 1976 vintage. The swap should be an easy one for you to do. Personally, I think It's a great swap in.

 

[Zuni]

...when I checked my last fill, I got an average of 26 MPG on an unimproved engine of 1976 vintage.

Dave, I'd like to hear more about that, and how you have it tuned. My stock '84 AMC 258 i6 / 4.2l gets about 16 with no team rush or Nutter (100% smogged up). That's the last time I checked mine, and that was averaging 40 MPH for 40 miles each way back and forth to work. Not many stops, but elevation changes from 4800- 7300.

I'll be starting my 4.0 head and MPI in about a month. Not expecting better mileage, just better drivability, and more power to drive the mountain roads. Might put a turbo on as well, haven't decided yet.

 

[coldwater]

Dave, I'd like to hear more about that, and how you have it tuned. My stock '84 258 gets about 16 with no team rush or Nutter (100% smogged up). That's the last time I checked mine, and that was averaging 40 MPH for 40 miles each way back and forth to work. Not many stops, but elevation changes from 4800- 7300.

I'll be starting my 4.0 head and MPI in about a month. Not expecting better mileage, just better drivability, and more power to drive the mountain roads. Might put a turbo on as well, haven't decided yet.

Nothing to it really. I installed a pretty big $$ Jacobs ignition in it, went to a webber carb, Clifford header and a big tube exhaust. I also gut every single bit of the emissions and junked it. I cruise it right down the highway at legal speeds, no babying it. Never had to crack this engine open for any reason, and no team anything done to it, It's just good old stock AMC goodness. Even my last bone stock 7 with the AMC 258 i6 / 4.2l put out a solid 18-20 mpg, ( after stripping the emiss) and I had a AMC 232 i6 that got about the same. A good high energy ignition system is gold in a AMC 258 i6 / 4.2l , and you can get some pretty impressive results without having to break into the engine for major mods. All mine are simple bolt ons upgrades. I looooove that little 358 AMC engine. Ask Ellwood what he thinks of his new system.

 

[Zuni]

Thanks Coldwater. I'm still doing the 4.0 head MPI thing just because I drive it at elevations from sea level to 8500 ft regularly and I think MPI is the way to go for my situation.

Thanks again

 

[baker9713]

I'll throw in my 2 cents. I've done quite a bit of wheeling with cj's, all with the AMC 258 i6 / 4.2l . I have never had a need for more power than I could get from the AMC 258 i6 / 4.2l . Now I've never had a cj with a v-8, so maybe I'm missing out, but those AMC 258 i6 / 4.2l 's are good motors and have never let me down. The carb they usually came with (Carter BBD) does not handle inclines. Once that is replaced with a better off road carb or fuel injection, it does just fine. Just my opinion.

 

[CJ]

The AMC 258 i6 / 4.2l is one rock solid 7 bearing six cylinder. About the finest 6 ever produced by just about any vehicle manufacturer...

I had one that I could not kill. I tried! Drove home one time with a broken radiator, the engine got so hot it melted the pluf wires - I had to stop it by putting a rag in the carb throat.

Replaced the radiator, wires and a few other things then drove it for many year.

When the car died, we did a brick in... Drained the oil and water then bricked the accel pedal... It ran until it got hot then slowly died - never blew up! I sold the car and the person who bought it drove it for another few years!

That being said - sorry - I'm a HP junkie! Give me a V8 any and all day!

 

[LongHorn]

So I'm going to pull the 304 out of my CJ5 to fix an oil leak. Around the same time, I found a running 258 for cheap. From what I hear the 258 is evey bit as good as the V8 and even better in some cases.
So here's the question: How difficult is this swap? I imagine that the engine mounts will have to be relocated, but what else do I have to watch for?

You must have heard that from the same chick that told you "Size doesn't mater". "There's no replacement for displacement"

 

[CJ]

So here's the question: How difficult is this swap? I imagine that the engine mounts will have to be relocated, but what else do I have to watch for?

I forgot to answer the original question...

It's a pretty easy swap as everything you has been produced and was available from the factory!

You just need to do a little homework and get the correct parts.

Yes - one of the frame mounts will have to be changed as well as the actual rubber mounts. So will the exhaust and all the assorted normal engine swap pieces.

 

[Petescj]

Which is exactly why you should look around for a decent V-8. Add a new radiator shroud to the parts list. Its alot of little unnessacary stuff to do when another Amc V-8 would bolt right in literally. Plus if you find one complete all your acc. parts ( starter , carb etc. ) can be kept for spares saving you more cash down the road.

Yes - one of the frame mounts will have to be changed as well as the actual rubber mounts. So will the exhaust and all the assorted normal engine swap pieces.

Im not bashing the AMC 258 i6 / 4.2l . They are nice little stump pulling motors and Ive had my share of them. Theres one in the Scrambler right now. But when someone says " I found a AMC 258 i6 / 4.2l cheap " I take it hed like to and is trying to save money. Another bolt in Amc V-8 is the way to go.