4.2 intake on a 4.0 head

[tinman]

Doing the conversion, I go to put my 81 intake on and it hits the #4 exhaust tube. Well, after doing some searching on here, it sounds like I need to do some "minor" modifications to it. I start grinding a little bit off of the bottom of the intake, then a little more, and before I know it I've made my way into the water jacket.
So, a couple of questions. First, should I weld the intake back up and "dent" the exhaust tube to make it fit? And second, should my '81 intake even fit? I thought the 2 barrel intakes would all fit with the 4.0 head.

Mine is a CA model if it makes a difference.

On a side note, before I pulled my stock engine out, I put it on the dyno to get the before numbers..... 88 hp and 166 torque. Does that sound about right?

 

[IOPort51]

Hint:
line up the intake ports with the manifold and mark the location with a felt pen. then put the gasket on the head where it line sup with the ports, put your manifold where it will fit and look at the marks you made on the gasket. It is possible to get the manifold 1/4 or 1/3 a hole off and not really be able to see it.

I also made some larger washers to bridge the larger spaces between the intake and exhaust and used studs instead of bolts, made it a lot easier.


I like to assemble all this before I put the head on, makes torquing a bunch easier.

 

[yellow85cj]

Of all of the 4.0 swaps I have read about and fitting the intake and exhaust on mine, I have never heard of a problem like yours.

Did you mod the intake as IO shows? That would raise the intake a bit. If you mounted the intake on the alignment pins of the 4.0 head, it would be lower and hit the exhaust as you show.

I used a little different method than IO. Here's how I did mine.

https://picasaweb.google.com/85YellowCJ7/40HeadSwap#

 

[tinman]

I couldn't find anybody either until I talked to Rescue Diver, and found out he had to do something similar on his. I do have your pics saved on my computer, so I was in the middle of doing it the way you guys say when I ran into my little problem. Now it's off to find a welder to fix my impatience!

 

[IOPort51]

I am very impressed with the way you saved your EGR valve. I really want to do that with mine.

I forgot to mention that I did do a bit of hammering to the exhaust header to clear the bottom of the intake.

Of all of the 4.0 swaps I have read about and fitting the intake and exhaust on mine, I have never heard of a problem like yours.

Did you mod the intake as IO shows? That would raise the intake a bit. If you mounted the intake on the alignment pins of the 4.0 head, it would be lower and hit the exhaust as you show.

I used a little different method than IO. Here's how I did mine.

https://picasaweb.google.com/85YellowCJ7/40HeadSwap#

 

[Rescue Diver]

I did the same as IO and bench fit it all using a marker. The intake does need to sit higher, on top of the alignment pins instead of on them to line up well with the intake ports, but you'll need to do just a little grinding on the bottom of the intake alignment pin flanges below the pin hole so it sits evenly above the pins. Even with it mounted higher on the head where it lines up with the ports, you can still expect to have to dent the header a little on number 4.

And like IO said, it's definitely easier to assemble and torque down the head, intake and exhaust on the bench and just install the whole rig as one piece on your short block.

 

[Sasquach]

To add to what Rescue Diver said, The Mopar intake manifold which is designed to fit both the 4.0 and AMC 258 i6 / 4.2l head has two different dowel locations depending on what head you are fitting to.
So this would verify that it sits up higher on the 4.0 head and after looking at mine it is nearly 1/2".

 

[tinman]

Got the intake back from the welder today. Fits really nice and I didn't even have to hammer on the exhaust! I was happy with the $35 price tag too.

 

[IOPort51]

looks like he did a pretty good job for you.

check it with a straight edge, be sure it's still flat on the gasket surface.

 

[tinman]

How do you fix it if it's not?

 

[IOPort51]

How do you fix it if it's not?

you visit a machine shop and give them, hopefully, a fair price and they make it flat again with a very large and expensive piece of machinery.