Silly Exhaust Manifold Bolt Size & Installation Question.....

Mopar Exhaust Systems

  1. soundhd

    soundhd Well-Known Member

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    Just purchased a copper exhaust manifold gasket kit for my 70 Roadrunner (stock 383 auto).
    What size are the "stock" exhaust manifold bolts (not studs) (insturctions list 5/16"-18 or 3/8"-16).
    Torgue settings for both sizes of bolts on the instructions are different using Oil or Moly...what do they mean by Oil or Moly?
    Torque setting on instructions are: (ok to use?)
    Grade #5: 5/16"-18: with Oil - 96 inch lbs.;
    Grade #8: 5/16" 18: : Oil - 20 ft. lbs. ; Moly 13 ft. lbs.

    Grade #5; 3/8"-16: Grade #5: Oil - 15 ft. lbs.
    Grade #8: 3/8"-16: Grade #8: Oil - 35 ft. lbs.; Moly 23 ft. lbs.


    Also is it OK to re-use the old bolts or should I purchase new ones? If purchase new ones what type should I get..Grade 5 or 8? (assume #8 is best)
    Want to make sure I do this right the first time.

    thanks
     
    Last edited: Oct 13, 2017
  2. aeon280

    aeon280 Well-Known Member

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    I'm not sure on 383 but 360 is 5/16 x24 if i recall. Go with new bolts. Exhaust manifold bolts are under extreme conditions throughout their lives and the constant heating and cooling takes a toll. Reusing the old ones will more often than not result in chasing exhaust leaks. When removing them make sure you use a good penetrant several hours in advance. Go with grade 8 replacements if possible or even some ARP sourced hardware thats even stronger than grade 8. Also make sure you chase the holes before installing new hardware. The ones that go into the water jacket get especially corroded an the trash in them can prevent proper torquing on the new bolts.
     
  3. PurpleBeeper

    PurpleBeeper FBBO Gold Member FBBO Gold Member

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    Don't shoot me if I'm wrong, I'm going from memory. Your picture shows a 70 Road Runner convertible, so I will assume big block.

    1. "Stock" was only studs, no bolts.
    2. Oil or Moly --> some people put oil or grease containing "molybdenum" on bolts before tightening. Typically, you need to torque them differently when "wet"... I think a little bit less (?). I normally torque my exhaust manifold nuts/studs dry personally.
    3. "Stock" studs are 3/8-16" threaded on the block side & 3/8-20 (or 24) (fine thread) on the outside where the bolts go.
    4. Grade 8 bolts are preferred. They are harder, but more brittle too. I'd probably go Grade 8, but for exhaust manifolds I "think" you could get by with Grade 5. The Grade 5's would be more prone to breaking BUT also much easier to drill out & re-tap if you happened to break off one (I've broken a couple Grade 8's over the years).

    Now that I think about it.... go Grade 8 if you have headers and either one if you have stock exhaust manifolds. Header flanges aren't all that smooth and sometimes you have to torque them a little more go get them to seal. Unless warped, stock manifolds are usually pretty smooth.
     
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    • 440+6

      440+6 FBBO Gold Member FBBO Gold Member

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      3/8-16 grade 8 and you need to put pipe dope or sealer on the threads because they are in water jackets, drain the radiator before you remove the old ones.
      That's why I prefer studs if you can use them.
      And Greg, take care of that car, you know I want it.
       
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      • mopar 3 B

        mopar 3 B Well-Known Member

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        If you just got to have bolts. Header bolts or srainless steel.
        Even with headers use all the studs you can. They hold the gasket in place and help align the header.
         
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        • 5.7 hemi

          5.7 hemi FBBO Gold Member FBBO Gold Member

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          Use studs if ya got aluminum heads!
           
        • soundhd

          soundhd Well-Known Member

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          Thanks for all the replies and info. This is my first Mopar so still learning. Car was "sort of restored" about 13 years ago and I am finding out a lot of things were done incorrect and on the "cheap". This forum has been a life & time saver for me. Anyway I found and ordered a complete stud kit from Mancini Racing so going that route. Did not know there were the different sizes and types of nuts associated with the kit and also did not know the bolts went into the water jacket.....would of "'freaked out" if & when I pulled the first bolt off and had coolant running out......LOL

          Thanks again for all the info

          PS: 440+6 who are you? Send me a PM
           
        • Billccm

          Billccm FBBO Gold Member FBBO Gold Member

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          I've been watching this thread because I'm going to tackle the same job myself in December. Please update on your progress. Also can you post the link on which stud set you bought?

          I'm going with remflex gaskets. Many of my mopar friends have had good results with remflex.

          Thank you for any advice from your job here.
           
        • soundhd

          soundhd Well-Known Member

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          I ordered an exhaust manifold stud kit from the Mancini Racing web site. They have all the different stud kits for the different size Mopar engines. I also bought a Mr. Gasket copper gasket set #7167 from a local auto parts store. Will update how this all goes. A couple Mopar buddies have used those and so far have worked great. The only thing I found with the gasket kit on-line instructions are the torque settings are different then the shop manual and what type of lube (Oil or Moly) used also have different torque settings. Still have to figure the Oil vs Moly thing out. First time I have seen that. Big learning curve for me.
           
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          • miller

            miller FBBO Gold Member FBBO Gold Member

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            That has to be for the nuts, onto the studs. Yes, torque used, on any 'wet' threads will be different.
            I'll toss this in...studs into heads, I've always used Indianhead shellac sealer there.
             
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