Broken intake manifold

[Adeaux10]

Hi, Im fixing up an 83' AMC 258 i6 / 4.2l CJ7 that I bought in November. This is my first Cj and figuring it out as I go. It is in pretty rough shape but still runs. The PO's stripped it down to bare necessities but it seems to be mostly stock. Im in the middle of swapping the Weber carb for the 2100 and have the intake and exhaust manifolds to change gaskets and clean them up a bit when a 500 gallon air tank rolled onto it snapping it in two. (too retarded to explain) The intake looks to be cast iron and uses the exhaust heater system. I just ordered the only Cj intake i could find from ebay but it is water cooled. Can I use my old exhaust manifold and just cap the heater ports, or do I need to find one to match? Alternately, can I weld the broken one back together? Ive heard it can be tricky. Any thoughts would be helpful, Thanks.

 

[IOPort51]

Use the aluminum manifold and run one of the heater hoses from the water pump to the manifold and from the back of the manifold to the heater.
Welding a cast iron manifold in tricky and the last resort.

 

[Rescue Diver]

Hi, Im fixing up an 83' 4.2L Cj7 that I bought in November. This is my first Cj and figuring it out as I go. It is in pretty rough shape but still runs. The PO's stripped it down to bare necessities but it seems to be mostly stock. Im in the middle of swapping the Weber carb for the 2100 and have the intake and exhaust manifolds to change gaskets and clean them up a bit when a 500 gallon air tank rolled onto it snapping it in two. (too retarded to explain) The intake looks to be cast iron and uses the exhaust heater system. I just ordered the only Cj intake i could find from ebay but it is water cooled. Can I use my old exhaust manifold and just cap the heater ports, or do I need to find one to match? Alternately, can I weld the broken one back together? Ive heard it can be tricky. Any thoughts would be helpful, Thanks.

First thought is, your engine, or at least the intake and exhaust manifolds are from a 1979 or older Jeep. They're a matched set and can not be mixed. They switched to the aluminum intake in 1980. The pre 1980 intake and exhaust bolt together under the carb with four studs. Look at the length of the flanges where the common bolts of the intake and exhaust manifold clamp them to the head. You'll find that the cast iron intake has a really long flange requiring longer bolts than the aluminum intake/exhaust set. That means you can't use the aluminum one with the 1979 or older exhaust manifold anyway. You'll either need to buy a 1980 or newer exaust manifold to go with the aluminum intake you purchased, or you'll have to find another pre 1980 intake. Ebay is your friend on this one! 1980 and newer exhaust manifolds go pretty cheap on there new.



Second thought is, is your broken cast Iron manifold a two barrel or one barrel? I have a clean, perfect condition, pained one barrel cast iron intake manifold left over from my 4.0 head swap that I'll let you have for $15 plus actual shipping costs if that's what you're looking for, but I'm not sure who makes an adapter to put an MC2100 two barrel on a one barrel intake, or if I'd even think that's a good idea because of the restricted flow if they do make one.

I do have a recently rebuilt carter YF carb that I would give away for peanuts with the one barrel intake if your just wanting to get it back on the road cheap.

Personally, I'd stick with the aluminum intake you already bought, buy a 1980 or newer exhaust manifold that works with it, route the heater hose through the intake, and run the MC2100.

 

[Adeaux10]

Thanks RD, I definitely want to get that 2100 up and running. The broken intake is a two barrel, so I'll take your advice and find a newer exhaust manifold to match. I noticed that the set was older when I bought the gasket set at O'reilly and had to return it for the '79

Do you know how the aftermarket exhaust manifolds (incl. tubular) fit in relation to just buying an original?

 

[Rescue Diver]

Thanks RD, I definitely want to get that 2100 up and running. The broken intake is a two barrel, so I'll take your advice and find a newer exhaust manifold to match. I noticed that the set was older when I bought the gasket set at O'reilly and had to return it for the '79

Do you know how the aftermarket exhaust manifolds (incl. tubular) fit in relation to just buying an original?

You have to buy an original because the later model tubular 4.0 exhaust manifolds will not match the shape of the exhaust ports on your head.

Are you sure the whole engine you have is not pre 1980? You can verify it by doing a search on the number on the side of the engine block. Either way, the pre and post 1980 AMC 258 i6 / 4.2l intake and exaust manifolds are interchangable as full sets. As long as both manifolds came from the same era, they'll fit 79 and older as well as 80 and newer. Since you're switching to the 80 and newer set, a trip to the hardware store for some shorter grade 8 bolts will be needed. Like I said before, the older cast iron intake manifold, and the exhaust manifold that works with it take a longer bolts.

***EDIT***
I just noticed you were asking about aftermarket tubular exhaust manifolds. I only know what I've read on the net about them. Aftermarket headers for the AMC 258 i6 / 4.2l aren't very cheap. They cost a lot more than a brand new replacement stock type manifold will run you on ebay. You'd have to get your exhaust modified to bolt to it. I've heard some people say they had issues with the flanges being a different thickness than the factory manifold, possibly requiring a little engineering on your part? As for performance gains, maybe someone else that's installed a header on an otherwise stock AMC 258 i6 / 4.2l can tell us their results???