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Last night I bought a real nice cast #7120 4.0 head to do the swap. I really kicked around going V8, but since I have 2 AMC 258 i6 / 4.2l motors, I'm going to do the swap and like it. I'm also getting the block to the machine shop. I paid $200.00 for the head which came with the throttle body, (Not going to use), intake manifold (not going to use) Valve cover (might not use) all the push rods and head bolts and a complete felpro gasket set. Instead of asking a lot of questions that has been hashed out before I'm trying to do searches on here and if I type in 4.0 head swap, it just comes up that my search don't match anything. WTH am I doing wrong here? There has to be a lot of info on here on that subject. Any Ideas would help. I'm probably doing something wrong.
Last night I bought a real nice cast #7120 4.0 head to do the swap. I really kicked around going V8, but since I have 2 4.2 motors, I'm going to do the swap and like it. I'm also getting the block to the machine shop. I paid $200.00 for the head which came with the throttle body, (Not going to use), intake manifold (not going to use) Valve cover (might not use) all the push rods and head bolts and a complete felpro gasket set. Instead of asking a lot of questions that has been hashed out before I'm trying to do searches on here and if I type in 4.0 head swap, it just comes up that my search don't match anything. WTH am I doing wrong here? There has to be a lot of info on here on that subject. Any Ideas would help. I'm probably doing something wrong.
If you have the Half inch head bolts on your AMC 258 i6 / 4.2l , the head will bolt right on no issue. If you have the smaller 7/16 head bolts you will need a spacer in all four corners to center the head correctly. You can make it or purchase here Clifford Performance: 17-2001 Centering Washers
There has been plenty of debate about the water jackets on the passenger side of the head as to whether they need to be sealed or not. The replacement head gasket has no holes where the water jackets are so it probably is unnecessary but IMHO you may as well just get some packing peanuts and JB weld and seal them anyway. It honestly wont hurt anything and will only take you about the time it takes for the JB weld to set.
The rods, rockers are also discussed alot but if I remember correctly the rods and rockers for AMC 258 i6 / 4.2l and 4.0s are actually the same PN but its been a while. SO I think it doesn't matter which you use. I know for a fact the rockers are the same AMC 258 i6 / 4.2l -4.0 but not sure on the rods. In my AMC 258 i6 / 4.2l /4.o hybrid on my first CJ I used the 4.0 rods for good measure and it ran fine.
I did not change my stock AMC 258 i6 / 4.2l cam and it did not affect anything from what I could tell. I had MPFI on mine so I'd say that its just your personal preference on the cam. I think it is safe to say that pairing with a better breathing cam will take advantage of the superior intake runner/fuel atomization properties of the 4.0 head would be worth your time but not necessary.
You will need a 4.0 header. The CJ intake will need to be shaved in some spots to clear the header. You will need to fit an shave to your application.
That all there is to it. You can use the torque specs from a 4.0 or AMC 258 i6 / 4.2l equipped vehicle service manual for everything. I used a standard replacement head gasket for a 4.0 because i believe i read somewhere that the AMC 258 i6 / 4.2l and 4.0 have the same bore just different stroke, I am sure someone will correct me if I am wrong on that.
If I may offer one tip, assemble the head and manifolds before you put the head on the engine. Easier to line up the manifolds, that requires a bit of metal removal, and a lot easier to torque the manifold bolts. I also used studs rather than bolts and made over sized washers to hold the manifolds in place. I had the head welded and decked with a 3 angle valve job. I used an exhaust header but the 4.0 exhaust will work quite well. try to find one that isn't cracked or one that looks to have been repaired properly.
Thanks IO great info. I'm glad I decided to go that route. The exhaust manifold that the guy had was cracked, so I figured I'd go with a header. Some time back, I bought a new Offenhauser DP intake for a AMC 258 i6 / 4.2l that I hope I can use with some modification. I'll have AMC 258 i6 / 4.2l head bolts and I got the 4.0 head bolts. The cam, I'll have to wait and see, but will probably go with a little bigger than stock. Seems that chrome or all aluminum valve covers can't be had for the 4.0. The one I got with the head, was painted black with wrinkle paint, but I took a magnet to it last night, and it must be aluminum. Anybody ever media blast and polish a stock 4.0 valve cover? Again thanks for the info, I'll use it.
Thanks IO great info. I'm glad I decided to go that route. The exhaust manifold that the guy had was cracked, so I figured I'd go with a header. Some time back, I bought a new Offenhauser DP intake for a 4.2 that I hope I can use with some modification. I'll have 4.2 head bolts and I got the 4.0 head bolts. The cam, I'll have to wait and see, but will probably go with a little bigger than stock. Seems that chrome or all aluminum valve covers can't be had for the 4.0. The one I got with the head, was painted black with wrinkle paint, but I took a magnet to it last night, and it must be aluminum. Anybody ever media blast and polish a stock 4.0 valve cover? Again thanks for the info, I'll use it.
Sorry Your info was great. It was Sunday morning and I was so into reading that I didn't pay attention when I replied and IO is all that came to mind at the moment. I really appreciate the information it was what I was looking for.
Just want to do a shout out to some pros on here that gave me some excellent information on this head swap that will turn what I thought would be a little tough swap to a can do swap. IO Port, Thisguyyouknow, and Yellow85cj. What's gonna be cool, is when the buds stop over and see my progress, they'll think I'm a genius.....LOL.......
Just want to do a shout out to some pros on here that gave me some excellent information on this head swap that will turn what I thought would be a little tough swap to a can do swap. IO Port, Thisguyyouknow, and Yellow85cj. What's gonna be cool, is when the buds stop over and see my progress, they'll think I'm a genius.....LOL.......
Here is the endstate more or less of my 4.0 swap. The only stuff missing in this pic are my fan controller, speedo cable, and cruise control servo that are now mounted on the FW
1980 cj5 258ci straight 6, 31x10.50's. Partial Teamrush iginition upgrade, MC 2150 Carb. 4.0 head swap, factory header. I call him "Eugene".
Dad's jeep when he raced in the 70's. Cj2 running gear, ford 300 cu in 6 cyl with 3 deuces. Fiberglass model T body and hand laid fiberglass hood. welded 5.38 gears and beer keg fuel tank. see avatar
Wife's: Black 04' Liberty with all the bells and whistles.
