I was scrubbing my intake manifold with a wire brush in preparation for some engine paint. I noticed the bolt below was loose and then discovered it was rusted completely off.

Can someone please educate me about the function of this bolt - does it hold the intake and exhaust manifolds together? Is it threaded into the exhaust manifold or go through? What repair is recommended?

Car is '72 Ply Scamp, obviously 225 /6. Engine is all original with 39k miles. Engine runs fine now.

Yes that hold the manifolds together, although factory is should be a stud with a nut on the top...looks like you will have to pull the stack apart and extract what's left and get a stud or bolt to replace it.

-D.Idiot

Yes, it's one of three essential bolts that hold the intake and exhaust manifolds together. There is a steel shim gasket between the two (if its original) and it seals the heat flapper door area which provides heat to the base of the intake manifold for better fuel atomization...etc.
I did a super 6 conversion and I used a newer exhaust manifold and the hardware included a stud which threaded into the exhaust manifold and a nut is threaded on top to provide the clamping power.
The hole does not go through, like you asked. So that wont be a leak point but you may develop a leak at the area below the intake where it mates to the exhaust manifold since you have lost the inside (closest to the head) clamping force this provided.

I am going to disagree with it being a stud. I believe the early manifolds had a bolt as I have had 6 different manifolds 3 early and 3 later and the earlys all had the bolt the laters all had a stud. I also noticed the bolt is large then the stud or the other way around I can't recall at this moment.

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2006 Jeep Commander
2013 Chrysler 200

1964 Valiant 4 Door
1965 Plymouth Barracuda
1967 Chevy Camaro

Yep,
My '72 Valiant originally had a bolt there as well.

How critical of a repair do you view this, if there is not currently a leak?

The engine is running great and by the looks of the bolt I haven't had a functioning bolt there for a while. Although the bolt is obviously broke, I feel like since there is no functional loss, "if it isn't broke don't fix it." Is there a risk of causing more damage if I do nothing?

However, I will start looking for a replacement exhaust manifold to have on hand. Any suggestions where to find one?

If it were me I would leave it alone. If it ain't broke, don't fix it kind of thing. It might be possible to drill it out and put a bolt through it without taking anything apart.

Sam

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I'd also leave it alone unless a leak develops there. The remnants/rust of the bolt may be enough to keep it tight. It's been like that a while.

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ski

6inarow-makemego,

My 74 Swinger came with a bolt in that location. Since the rebuild I replaced all three locations with stainless steel bolts so that doesn't happen again! Something you may want to consider when it does start leaking.

You can view pictures of the bolts by clicking on the red link below my name.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

All your points are valid. Had you not attempted to do some detailing under the hood you would have been oblivious to it. It isn't critical just a little time consuming because there is no guarantee that all the exhaust/intake studs will be removable without breaking so you can potentially open a can of worms.
If you are a stickler for detail then fix it but if you don't have a leak now and it runs good then just wait and collect the bits you need ( such as intake/exhaust gasket, extra intake/exhaust studs and nuts, gasket between both manifolds, down pipe gasket...etc)when the leak manifests itself.
Someone on the forum should have a manifold or you could just have yours repaired and at such time I would use a stud and a nut on top instead of a bolt.
Your exhaust manifold has the open choke well that requires a hard to find gasket. If all of that stuff is in good shape (which it appears to be) I would have the present manifold repaired.

Heh. I'm doing some intake/exhaust work on my '73 Dart and this bolt (yes, a bolt on the 73) was completely rusted through. I got a used but decent 80's era mani on ebay. Came with a stud, which easily snapped when I was testing intake/exhaust mani fit-up. I inspected the broken stud and saw that it had cracked at the top thread on the mani and rusted about half way through. Based on these, I wonder if heat cycling (especially if expansion/contraction rates differ between in and ex) puts extra stress this fastener. Anyway, I now have two exhaust manis heading to the machine shop to address the same "broken center fastener" problem.

What do y'all think I should use as replacement fastner? Grade 8 or stainless bolt/stud?

Thanks

I think I favor a stud. That way the only threads you wory about are the ones up by the intake manifold. The threads by the intake manifold are not subjected to the heat of being in the exhaust manifold and will likely survive longer and be less likely to get seized because of it.

Anyone know the exact length, size, and pitch of this bolt? I needs one for a reassembly. Would prefer not to use a stud.

Thanks for all the replies. I will now begin to gather the necessary parts for making the repair, once a problem develops. I will post a parts wanted ad, but if any one has any of the components for sale, please send me a private message.

Also, please let me know if there are other parts I should hunt.

NEEDED:
intake/exhaust gasket
intake/exhaust studs and nuts
gasket between both manifolds
down pipe gasket
open choke gasket

Thanks, Stephen

You wont' be disappointed with stainless bolts and some Never Seize, (silver snot) and RemFlex gaskets. They work very well.......I have tired to use the stock FelPro gaskets and they never last long.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG