Connecting rod nuts

Slant 6 Engines

  1. circlepilot

    circlepilot FABO Gold Member FABO Gold Member

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    Are OEM connecting rod nuts rated at grade 8? (225/6)
     
  2. RustyRatRod

    RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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    At least. Possibly grade 10 or even 12.
     
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    • Phreakish

      Phreakish Well-Known Member

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      But don't use hardware store grade 8 nuts (if that's your plan).. The flange design of con rod nuts is as important as the material/strength.

      Arp makes nuts in various threads and are cheap enough to not mess with hardware store junk.
       
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      • circlepilot

        circlepilot FABO Gold Member FABO Gold Member

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        It was never my intention to use "hardware store nuts." I was trying to find some specifications on OEM nuts without much luck. In my application, I believe it is not necessary change my rod bolts, (however, I may just cave and spend the money for the new bolts and resizing the rods, est. $150.00) but would like to just change the nuts. The OEM nuts are not "flange nuts, which seems to be all that ARP has. Fastenal has a grade 8 3/8 24, yellow zinc plated nut, (made in China) which seems to be where all this stuff is coming from.
        Norm
         
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        • Phreakish

          Phreakish Well-Known Member

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          Was just checking.

          The nuts aren't the critical part. The bolts stretch, which can cause failure if reused. The nuts, unless damaged, should be perfectly fine for reuse.

          My rule of thumb has ways been that if I can't measure a reduction of the major diameter (or in the full diameter Shank, but that part is often unaffected) of the bolts, then they can be reused. If there is a definite reduction in the thread major diameter (.005 or more) then just replace them. Calipers are OK, but I much prefer a mic for this check.

          This is also subject to the intention of the engine (performance builds should always get new hardware) and of course on how much it would suck if the reused hardware fails. To me, $150 is cheap insurance. Not everyone is in the same boat.
           
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          • MoparLeo

            MoparLeo NRA PATRON LEVEL LIFE MEMBER FABO Gold Member

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            You really can't "afford" not to replace them. Cost of engine Vs. cost of bolts....
             
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            • 413

              413 Well-Known Member

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              The threads are rolled not cut. You shouldn’t change just the nuts. You don’t need flange nuts on stock bolts. Why do you want to change the nuts? That idea is crazy!

              Yes ARP Is great quality and worth the price. Do it right or leave them stock.

              If it’s from direct connection or mopar performance don’t use them.
               
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              • volaredon

                volaredon Well-Known Member

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                I'd like to know who their supplier was. I know that Chrysler did not make their own hardware.
                I've rebuilt several engines over the years, have never replaced the rod bolts in any, never had an issue. But every engine I have been into has been run of the mill daily driver to this point.
                On my current build my engine came to me as an incomplete basket case. I didn't get pistons or rods with it. I lucked into a set of NOS rods still in mopar boxes. I certainly ain't worried about replacing those rod bolts.
                 
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                • 65 Cuda 340

                  65 Cuda 340 FABO Gold Member FABO Gold Member

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                  I overhauled a high mileage 440 long time ago, without replacing the original rod bolts, and one of them broke, doing major damage inside the motor.

                  NOS slant six rods - I agree there is no reason to replace their bolts.

                  OP mentioned above about not wanting to resize the rods. I know resizing the rods it recommended when replacing bolts, but I have done so without resizing them (or, more accurately, after they had already been resized with the original bolts in them). This was a rebuilt 440 short block that replaced the one that blew up mentioned above. Never had a problem.
                   
                • Hyper_pak

                  Hyper_pak Old School Chrysler Fan

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                  If you replace with the ARP slant bolts they are larger. They wont drop in without problems. That is why you need to resize them. Several people have lost engines after switching bolts. I have never had any trouble with DC Bolts.
                   
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                  • circlepilot

                    circlepilot FABO Gold Member FABO Gold Member

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                    I have since changed my bolts out with the ARPs. I noticed that while I was pressing them in, on three of the rods, the head of the bolt (only on one side of the rod) left a little bit of a "rub mark" on the rod itself. All of the rods are at the machine shop being resized, balanced and the pistons installed. My crank shaft is being balance also.
                     
                  • RustyRatRod

                    RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                    ARP made rod bolts for Mopar Performance.
                     
                  • 413

                    413 Well-Known Member

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                    Are you sure of this? What year did this take place? MP was famous for finding the cheaper supplier and sacrificed quality to do it.

                    my machinist said the worst rod bolts he ever saw were in a MP package, and don’t use them.
                     
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                    • RustyRatRod

                      RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                      100% positive. I bought several sets through the 80s. They came in an ARP package with MP logo. Bolts had ARP stamped right on them.
                       
                    • RustyRatRod

                      RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                      They came like this. My bad. It wasn't an ARP package, but the bolts had ARP stamped right on the heads. It has been some time ago. lol

                      MP BOLTS.png
                       
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                      • famous bob

                        famous bob mopar misfit

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                        I replaced the rodbolts in a hemi superstock type engine w/ mopar bolts , didnt change anything , knocked them in w/ a hammer while holding the rod in my left hand.< tells you how tite they were .
                        That engine was raced for a lot of yrs. , and as far as I know are still in it -----------
                         
                      • 66fs

                        66fs FABO Gold Member FABO Gold Member

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                        You are thinking of the recent Mopar Performance. The old Direct Connection stuff was great stuff as was the early Mopar Performance stuff. I bought a set of Mopar Performance rod bolts off eBay and when I got ready to build my 340, we noticed someone had put cheap bolts in the package, scrapped them.
                         
                      • Killer6

                        Killer6 Well-Known Member

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                        I also used a set of mid 80's DC/MP rod bolts on My slanty, don't recall them having ARP on them, but they withstood years of beatings. Ill advised zings to 7K, sustained & repeated 6K burnouts, put tens of thousands of miles on 'em. Still in that eng., about to tear the bottom end down this summer, took the car apart in '98.
                         
                      • RustyRatRod

                        RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                        I've done it many times with no ill effects. Everybody always recommends resizing the rods. Horse crap.
                         
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                        • famous bob

                          famous bob mopar misfit

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                          I hit the agree button-
                          If the parting lines are still lined up perfectly. The later stuff sounds kinda suspect !
                           
                        • circlepilot

                          circlepilot FABO Gold Member FABO Gold Member

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                          Let me bring you up to speed on the progress on my rods. Before taking my rods to the machine shop, I installed my new ARP rod bolts that I "pressed" in (with my press) making sure the bolt heads were seated. Then (as by the ARP direction sheet that accompanied the new bolts) I applied the ARP lube and torqued the nuts to 50ftlbs. 4 out of the 6 rods had obviously changed shape, as I could snag my fingernail on the joint. When I handed the rods over to the machinist, he agreed that those 4 rods had changed shape and said the other 2 probably have changed also. He also asked if I had loosened them and re-torqued them three times? "No, it wasn't in the directions." (unless I missed it) It was something he recommended. I hope to get them back in the next couple of days.
                           
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