1980-90 258 Exhaust Manifold fitment

[JeeperChris]

I need to know if the 1980-90 exhaust manifolds for the AMC 258 i6 / 4.2l will fit the earlier models. Mine is a '79 and from there down the exhaust manifold has that spot under the carburetor where the intake and exhaust bolt together. Since mine has a header right now there is a flat plate of steel bolted under the carb and some carb linkage bolted to two of those bottom bolts. I would love to be able to use the later model exhaust manifold as it does not bolt to the intake manifold and I can keep things the way they are.

So does anyone know for sure if the later exhaust manifolds are useable on the earlier models?

Thanks

 

[elwood blues]

Simple answer is yes, it "should". Here's a couple of stock pictures I found on the internet of the 2 different types of manifolds. There should be nothing to interfere with the newer model fitting with your older style intake manifold.

 

[JeeperChris]

That's exactly what I thought but I needed to hear it from you guys that have more experience with these things than I do.

Thanks Elwood!

 

[elwood blues]

You're welcome

If you do this, post up some pictures up so we can see how it fits!

 

[JeeperChris]

You're welcome

If you do this, post up some pictures up so we can see how it fits!

Absolutely!

 

[DaveMueller]

They're all compatible. I put the manifolds from an '88 YJ and an '88 Eagle on a '74 AMC 258 i6 / 4.2l .
Other than the block color, you can't tell them apart.

 

[JeeperChris]

They're all compatible. I put the manifolds from an '88 YJ and an '88 Eagle on a '74 258.
Other than the block color, you can't tell them apart.

Totally awesome!!! Thank you very much!

 

[CJKen51]

I know this is an old thread, but added a '82 intake and exhaust to my '79 AMC 258 i6 / 4.2l . Had to open up the locating holes on each end of the 82 exhaust manifold, to allow it to "move" up a little, so the center two exhaust bolts for cylinders 3 & 4 would be aligned. Also, the tabs on 2 & 5 had to be "deepened" a bit for bolt alignment. Ports all seem to match up fined. Also, you'll need shorter bolts all the way around as the tension tabs on the older style are off the face of the manifold a couple of inches. Keep all the tension washers for sure. I like having the O2 port in the exhaust manifold as well, for TBI system.

 

[CJKen51]

I know this is an old thread, but added a '82 intake and exhaust to my '79 4.2. Had to open up the locating holes on each end of the 82 exhaust manifold, to allow it to "move" up a little, so the center two exhaust bolts for cylinders 3 & 4 would be aligned. Also, the tabs on 2 & 5 had to be "deepened" a bit for bolt alignment. Ports all seem to match up fined. Also, you'll need shorter bolts all the way around as the tension tabs on the older style are off the face of the manifold a couple of inches. Keep all the tension washers for sure. I like having the O2 port in the exhaust manifold as well, for TBI system.

Also, the '79 Power steering bracket will not fit, without modification, when installing 80 & Up exhaust manifolds. Took a 1/2" deep cut about 2" long and it cleared the newer exhaust manifold. The Pwr steering bracket holes on the newer, aluminum intake lined up just fine.

 

[Martiiny]

Do you have a photo of the modified Power steering bracket after it was cut to fit the newer-style exhaust manifold?

 

[CJKen51]

I didn't take one before I mounted it. Hope this helps

 

[Martiiny]

Thanks for the photo. I have an1980 CJ5 that I am fitting a 1981 aluminum's intake and also fitting a Dorman cast exhaust ( unless you can suggest a better brand). On a rebuilt 1980 AMC 258 i6 / 4.2l . Any info or photos on hardware gaskets, tips would be greatly appreciated. I know it’s asking a lot but anything you can offer would be helpful doing this right the first time
Thanks much

 

[CJKen51]

You're welcome. When I used my Mahle gasket kit, it had the intake and exhaust gaskets riveted together. This is convenient for install, but ... I had to cut the rivets out because the exhaust was hitting on the rivet, which would have kept it from sealing the gasket material fully. "assemble" the intake and exhaust manifolds on your bench, on top of the gaskets, before intsalling them, so you can have a good look. I'll try to send a pic. Also, if using used manifolds, take the extra step to check for flat-ness with a straight edge. It's usually the old cast iron exhausts that warp the most. My used exhaust manifold was off, from outside to center by a good 1/8" or more. $35 each at the machine shop and both were flat, for a better seal. May not have that issue with a new Dorman, but check it anyway. Check the alum intake as well. A 24" builders square is what I used. I'll see if i can dig up a pic...

 

[Martiiny]

Thank you! Copy on the flatness checks for both mannifolds and I will look into the gasket you referenced. I have seen posts where people use. Entirely studs and nuts and some bolts and studs. Do you have any comments on this and is stainless or grade 8 something you would suggest. And lastly- any high. Temp or copper RtV on gaskets or plugs?

Thanks for your time, very much appreciated! Sorry for all the questions. I really want to only do once

 

[CJKen51]

happy to help:
I used the studs that were on the outboard end of my heads, while the rest were bolts. The outboard studs give you something to "hang" the exhaust manifold on while putting it all together. All grade 8. My gasket (package) said not to use any sealants so I didn't., but I was temped to use the copper spray. Stainless not necessary but would look dressier. Dressier? is that a word. Anyway, i did use a high temp copper style anti-seize on all the threads.
The pic shows the darker colored, intake gasket, that I had to trim so the exhaust manifold would sit flush against its own gasket. You can see the hole where there was a rivet. So I cut out a small right angle to clear the Ex manifold but left material enough to keep it all in one piece more or less. You only have to trim out that piece in two places. I believe cylinder #2 and #5. You may not have to trim yours.