1971 198 slant 6 manifolds

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Johnny71dusty

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There are 3 bolts that bolt the exhaust manifold to the intake manifold . 1) can’t find what size these are 2) do I need them ? Do they get any sort of gasket between them ? I don’t see why they would I’m trying to put my head back on this weekend a d those are only 3 bolts I don’t have .
Not looking for the studs that hold manifolds to head ; looking for the 3 bolts that hold manifolds together around where carb mounts
 
Ok I have that , can I put a blank on it ? I can’t find a thing about those 3 bolts anywhere .
 
Those are 5/16-18. Three inch minimum.

SlantSixFasteners.JPG
 
Do you recommend bolting them together tight first and then putting on them on head together ? Feel like it’s better to put on head and get them right there first but either way I can see alignment issues with these.
 
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The bolts are standard hardware fare, there is nothing special about them. Allthread would work fine too. The single bolt closest to the block is longer so best to measure before buying. There is a gasket that goes between them, it seals up the exhaust that comes up to heat the intake. Without it you will get blow-by all over. That gasket is nothing special, you could cut one out of gasket sheet material. I would bolt the two manifolds together first making sure they line up with each other for a good seal to the head, then install them as a unit.
 
OK, I measured the three bolts on a 83 slant six. The two on the outboard side are actually 4 1/2 inches long. The one in the 'center' is slightly shorter (I didn't take it out) but a longer one would work as it just goes inside the exhaust manifold. They are definitely 5/16-18 bolts. If you aren't sure of the size, just check the exhaust manifold as they thread into that.
 
OK, I measured the three bolts on a 83 slant six. The two on the outboard side are actually 4 1/2 inches long. The one in the 'center' is slightly shorter (I didn't take it out) but a longer one would work as it just goes inside the exhaust manifold. The outer ones are definitely 5/16-18 bolts. If you aren't sure of the size, just check the exhaust manifold as they
 
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All ofll the ones that I have messed with in the last few years have been 5/16-18 for the outer 2 and 3/8-16 for the one inboard of the carburetor. I have an 85 /6 a 74 /6, , and manifolds off of a few mid to late 70s ones laying here
 
You have the manifolds there with you. None of us has them. You are going to have to determine what sizes you have, because they used both 5/16 and 3/8 in that inboard hole. That's why the inboard hole on that gasket in the link up there and all of them like it have the inboard hole 3/8. I personally have never in my life seen one where the inboard hole was 5/16 OR a bolt and I've seen a lot of them. All of them I've ever seen were a stud and a 3/8 coarse thread stud. You've been told multiple times on more than one thread what the deal is. You're going to have to figure out what you have there based on the manifolds you have. We're not going to be able to do that for you.
 
You have the manifolds there with you. None of us has them. You are going to have to determine what sizes you have, because they used both 5/16 and 3/8 in that inboard hole. That's why the inboard hole on that gasket in the link up there and all of them like it have the inboard hole 3/8. I personally have never in my life seen one where the inboard hole was 5/16 OR a bolt and I've seen a lot of them. All of them I've ever seen were a stud and a 3/8 coarse thread stud. You've been told multiple times on more than one thread what the deal is. You're going to have to figure out what you have there based on the manifolds you have. We're not going to be able to do that for you.
The original one out of the car has 3 bolts . The new exhaust manifold / the single inboard one , is 3/8 thread in exhaust manifold . But the hole in the intake I got on eBay is smaller than 3/8 bolt can go thru it
 
OK, I measured the three bolts on a 83 slant six. The two on the outboard side are actually 4 1/2 inches long. The one in the 'center' is slightly shorter (I didn't take it out) but a longer one would work as it just goes inside the exhaust manifold. They are definitely 5/16-18 bolts. If you aren't sure of the size, just check the exhaust manifold as they
This is size and lengths match my 71 and the new set I got is the same
 
It's a good idea to have the exhaust manifold and intake put together and milled as one piece... more often than not the exhaust manifold warps and it doesn't line up for seal once it's all taken apart for say..' a head gasket change' or something. If you don't mill it all together....at least leave it all loose as you put it together till you get all the nuts tightened to the Head side THEN torque down 3 long bolts through the top.
The engineers left some play in the those bolt holes on the intake iirr for alignment to the head.
 
It's a good idea to have the exhaust manifold and intake put together and milled as one piece... more often than not the exhaust manifold warps and it doesn't line up for seal once it's all taken apart for say..' a head gasket change' or something. If you don't mill it all together....at least leave it all loose as you put it together till you get all the nuts tightened to the Head side THEN torque down 3 long bolts through the top.
The engineers left some play in the those bolt holes on the intake iirr for alignment to the head.
Well I didn’t do that lol . I got brand new exhaust manifold bur used a original early 70s intake manifold.
 
The original one out of the car has 3 bolts . The new exhaust manifold / the single inboard one , is 3/8 thread in exhaust manifold . But the hole in the intake I got on eBay is smaller than 3/8 bolt can go thru it
Then you're going to have to enlarge it.
 
The problem is the pre 72 manifolds used 5/16-18 bolts in all three positions. Chrysler changed the inboard hole to a 3/8-16 stud in 1973. The older exhaust manifold inboard bolt commonly broke off on replacing the exhaust manifold,so Chrysler resolved this by using a 3/8 stud. All you have to do is drill that hole in the intake manifold to fit the 3/8 stud. The stud is 3 5/8 inches long and is 3/8-16 thread. Slantsixdan has written about this solution in the past.
 
The problem is the pre 72 manifolds used 5/16-18 bolts in all three positions. Chrysler changed the inboard hole to a 3/8-16 stud in 1973. The older exhaust manifold inboard bolt commonly broke off on replacing the exhaust manifold,so Chrysler resolved this by using a 3/8 stud. All you have to do is drill that hole in the intake manifold to fit the 3/8 stud. The stud is 3 5/8 inches long and is 3/8-16 thread. Slantsixdan has written about this solution in the past.
Trust me. They did NOT resolve it. The 3/8 studs break too, almost every single time.
 
Just removed the 3/8 stud from to 2 exhaust manifolds today without any problem. If you put some ant-seize on the threads, that should take care of that issue.
 
Just removed the 3/8 stud from to 2 exhaust manifolds today without any problem. If you put some ant-seize on the threads, that should take care of that issue.
Correct, but Chrysler never did. I use the high temp ceramic brake grease. It goes from -40 to 3000 degrees F.
 
Depending on how far you want to take this, how about grade 8 fasteners.
 
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