Engine I need help with what head I have and what I should do moving forward

[Weebs74]

I bought a 1985 CJ seven from a guy who acquired it from someone who passed away. That builder did a lot of custom work. The current owner really had no idea what he was dealing with, and I bought it knowing it had fuel injection, on board air, lockers, 411 gears, and a bunch of other nice mods, including Clifford, intake and headers. It’s now several years later, and I developed some engine problems. Decided to swap the motor with a rebuilt that I picked up. I bolted everything today on the old motor, maybe something I should’ve done sooner and the head is most definitely different than the standard AMC 258 i6 / 4.2l L head that’s on the motor I purchased. The motor I bought was just board 60 over with new pistons and bearings. The old motor is missing some metal around the rear, main seal and leaks oil like a sieve and developed a weird knock recently. This is not my daily driver so I have options, but I’m not sure what I’ve gotten into.

The blue valve cover is the engine I bought, the one with the valve cover off is the head that is currently in my CJ. I also included the header gaskets for each of these engines for comparison.


Advice would be appreciated.

 

[Manic Mechanic]

Looks like you picked up a 4.0 not a AMC 258 i6 / 4.2l

 

[CJ]

Putting a 4.0L head on a AMC 258 i6 / 4.2l is a common modification.
Definitely a 4.0L cylinder head as it has rectangular ports for larger valves and better flow while a AMC 258 i6 / 4.2l has round ports.
Does the block casting number contain '444'? If so that is a AMC 258 i6 / 4.2l with a 4.0L head.

 

[Weebs74]

I’m not sure I understand… does the head on the engine where I pulled the Clifford header off of and the aftermarket exhaust does that look like the 4 L head?

 

[Weebs74]

I’m not sure I understand… does the head on the engine where I pulled the Clifford header off of and the aftermarket exhaust does that look like the 4 L head?

Specifically, the engine with the valve cover off. That’s the head. I’m trying to identify. I believe the other engine to be a stock head on a AMC 258 i6 / 4.2l L AMC.

 

[Weebs74]

Specifically, the engine with the valve cover off. That’s the head. I’m trying to identify. I believe the other engine to be a stock head on a 4.2 L AMC.

 

[Weebs74]

View attachment 106720

This is the engine I bought from a guy in NJ. Does this look like a stock amc AMC 258 i6 / 4.2l head. The intake and exhaust headers I took off this looked very stock.

 

[CJ]

Rectangular ports = 4.0L
Round ports = AMC 258 i6 / 4.2l
Does the block have 444 in the casting number? If so it's a AMC 258 i6 / 4.2l with a 4.0L head swapped on to it.

 

[Weebs74]

Putting a 4.0L head on a 258 4.2L is a common modification.
Definitely a 4.0L cylinder head as it has rectangular ports for larger valves and better flow while a 4.2L has round ports.
Does the block casting number contain '444'? If so that is a 258 4.2L with a 4.0L head.

Thanks so much for the message on this one. Yes the casting does have 444. So you think that this particular engine has a 4 L head?

Looks like you picked up a 4.0 not a 4.2

The engine I picked up is the one with the blue valve cover. The second picture with the valve cover off is a completely different motor. Can you clarify that for me? I think the engine that’s currently in my CJ, where I just unhooked the exhaust header maybe the 4 L head on a AMC 258 i6 / 4.2l L engine casting number is 444.

 

[Manic Mechanic]

Thanks so much for the message on this one. Yes the casting does have 444. So you think that this particular engine has a 4 L head?

The engine I picked up is the one with the blue valve cover. The second picture with the valve cover off is a completely different motor. Can you clarify that for me? I think the engine that’s currently in my CJ, where I just unhooked the exhaust header maybe the 4 L head on a 4.2 L engine casting number is 444.

View attachment 106721

The engine with no valve cover and the header beside it (round ports) is the AMC 258 i6 / 4.2l . The blue one with the valve cover on is a 4.0 or at least a 4.0 head

 

[CJ]

If the casting has 444 then the block is a AMC 258 i6 / 4.2l .
And as stated before, if the head has rectangular ports it's a 4.0L head. Round ports = AMC 258 i6 / 4.2l AMC 258 i6 / 4.2l head.
Many swap a 4.0L head on a AMC 258 i6 / 4.2l block. If that is done the intake and exhaust must be swapped for 4.0L hardware also.

 

[Manic Mechanic]

BTW just FYI

Boring an AMC 258 i6 / 4.2l .060 inches over is generally considered the absolute maximum limit and is not ideal for a reliable daily driver or long-term build, though it is often done. While it works for racing or mud-bogging, thin walls increase the risk of overheating, cylinder distortion, and cracking.