Engine Do I have a 4.2 or 4.0 no engine number

[KratostheBeast]

I have gone 4 pages looking for an engine ID trick eh I started on my lift and axles now turning to an engine canundrum eh My 80 CJ7 needing full resto engine runs good but I am puzzled by this. Stock AMC 258 i6 / 4.2l ? previous owner just drove it until his ground up CJ7 was done. No help from him. The head looks aluminum, but a magnet sort of sticks, valve train inside? Did the AMC 258 i6 / 4.2l or 4.0L have al option? don't think so from reading. No engine number on the wee pad on the block? A poor mans rub and xray no sign of impact marks. Then there is the lack of fuel pump. No cut out for the mechanical pump. No block off plate nothing. It was born this way eh So could it be a 4.0 L block? with aluminum head? Is it Chinese knock off? Help to forum discussion page 100+? or insights appreciated eh

 

[ram137]

It’s probably a 4.0. Chrysler went to fuel injection then and needed an electrical pump. That being said, if you’re able to keep it, do so. They’re bullet proof! Damn things last forever.

 

[Manic Mechanic]

Pics would help. No neither ever had an aluminum head although aftermarket ones are available at nearly 2k in price. But as stated if it's a 4.0 they're awesome motors

 

[CJ]

Besides the head, intake and exhaust manifold differences the biggest indicator and the easiest way to tell the difference between the AMC 258 i6 / 4.2l .and the 4.0L is the 4.0L HAS to have a CPS (crankshaft positioning sensor).
Make a careful inspection of the bellhousing and look for a sensor that lines up with the flywheel that could count the teeth. Depending on the bellhousing the location may be different.

 

[KratostheBeast]

Pics would help. No neither ever had an aluminum head although aftermarket ones are available at nearly 2k in price. But as stated if it's a 4.0 they're awesome motors

Ya I posted the pics a while ago... lol but a different Jeep site.. My bad eh An expert Jeep guy here in Lethbridge that has his own AMC jeep yard and works for a Hi performance parts store says 4.0 upgrade. Good for my I actually have the AMC 258 i6 / 4.2l crank already in it, though it is abut the only re boost done by the likely previous previous owner. So my odo is lying lol

 

[KratostheBeast]

It’s probably a 4.0. Chrysler went to fuel injection then and needed an electrical pump. That being said, if you’re able to keep it, do so. They’re bullet proof! Damn things last forever.

You know it eh I am following the New Comer performance YT page and blown away literally lol at the record numbers he acheived. Finally nice to know what I have and that it already has a AMC 258 i6 / 4.2l L crank. It runs wicked nice so the guru here says leave it til my last resto mod over the winter build it for my application.