340 Crank bolt threads issue

Small Block Mopar Engine

  1. Dartswinger70

    Dartswinger70 Only thing I ever bought new was a Fender Strat

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    I had recently sent out a crank for polishing. I have it on the bench and my crank damper bolt is going into the threaded hole kind of tight. Are there different threads fort he small block LA engine? I looked at both the bolt and the hole and cant see any damage. I had this crank for years and seem to think there was an issue years ago, but I am ready to use it now and am not wanting to wrench it in there if it is real tight. I learned to stop and ask years ago. Does anyone know the thread pitch and is there a thread chaser out there somewhere? :)
     
  2. Stephen Mulkey

    Stephen Mulkey FABO Gold Member FABO Gold Member

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    The shop that polished your crank should have a tap to chase the threads. Take both the crank and bolt and see if they could help you.
    Tool shops should be able to get at tap but could get expensive.
     
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    • Sterling

      Sterling Well-Known Member

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      Could be some dirt and/or rust on the threads of the crank or bolt. Try cleaning the crank and bolt, or try a different bolt. I have thread chasers for the bolt, and a tap for the crank. Should be 3/4-16 NF thread.
       
    • Locomotion

      Locomotion Well-Known Member

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      All small block Mopar balancer/damper bolts have the same thread. Damage can be caused by trying to install a tight balancer/damper using a stock length bolt and very few threads are engaging. I bought a longer bolt to get it started so more threads were engaged before it started pulling the balancer/damper in.
       
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      • Dartswinger70

        Dartswinger70 Only thing I ever bought new was a Fender Strat

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        makes sende, the bolt "starts" but gets tight after say two threads, it doesn't get in there very far. I was eying it up to make sure it was going in straight.
         
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        • toolmanmike

          toolmanmike Moderator Staff Member FABO Gold Member

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          Or use the proper tool. A little overkill for a 1 time use but they may have them available to use at the parts store or you can rent from the rent all.

          TP1330B.jpg
           
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          • 413

            413 Well-Known Member

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            Clean out the threads, use a tooth brush and brake clean for starters. Don’t use a tap, use a thread chaser.

            if your machine shop is nice they can help you.
             
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            • pittsburghracer

              pittsburghracer FABO Gold Member FABO Gold Member

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              I bought a kit after 30 years of doing it the wrong way and boy are they nice. You almost need it when building chevies because they don’t have a nice big bolt like Mopars do.
               
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              • toolmanmike

                toolmanmike Moderator Staff Member FABO Gold Member

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                They are slick aren't they!
                 
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                • pittsburghracer

                  pittsburghracer FABO Gold Member FABO Gold Member

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                  • pittsburghracer

                    pittsburghracer FABO Gold Member FABO Gold Member

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                    I would sleep with some of my tools but my cats get pissed. I love tools more than my ex wife.
                     
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                    • pittsburghracer

                      pittsburghracer FABO Gold Member FABO Gold Member

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                      Just used mine tonight. 6305D939-040B-4182-BC21-269EAEFF7CFF.jpeg
                       
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                      • JDMopar

                        JDMopar Well-Known Member

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                        I see what you did there! :eek:

                        :rofl:
                         
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                        • toolmanmike

                          toolmanmike Moderator Staff Member FABO Gold Member

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                          • Bobzilla

                            Bobzilla Well-Known Member

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                            The stock dampener bolt is just long enough to bottom out in the crank and damage the threads on the tip of the bolt if used to turn the engine over with no dampener installed. When you pull the bolt out it drags those damaged threads across the the crank threads.
                            I got really lucky and was able to run a tap in the crank and fix it when I did this. Then used a thread file to clean up the bolt threads.
                             
                          • Dartswinger70

                            Dartswinger70 Only thing I ever bought new was a Fender Strat

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                            Thanks for all the replies. It's funny how the mind works, I got home last night and was thinking "wait a minute didn't I buy a large size tap and die set year ago...?" I went out in the garage found the set which is a Craftsman set from the days when you could walk into Sears and they had such things in stock, so maybe 15 years ago or so I bought it. The size is 3/4-16 for the crank bolt. I chased the threads, and they were resistant the whole way down as in I had to chase the whole set of threads, but the bolt goes in properly now. Yes, I was thinking the threads were stretched or an impact gun was used etc. but there seems to be an explanation here so. Yes proper tools right?
                             
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                            • Scody21

                              Scody21 Just send it

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                              Taps / dies are for cutting threads.
                              Thread chasers are for restoring threads.
                              If you put them side by side, you’ll see the sharp cutting edges on taps and soft edges on the tread chasers...
                               
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                              • furrystump

                                furrystump Well-Known Member

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                                Talk to a machinist about thread chasers. Just a dull tap. The consensus is use a tap. If it is a quality tap you will not over cut the threads. They laugh at thread chasers. How far out of spec does a tap need to be to cause an issue?
                                 
                              • Coolvibes

                                Coolvibes Well-Known Member

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                                For a one time use, what is the most economical tool to buy that will both remove and re-install the harmonic balancer? This is for a 1965 273, and it does not appear to have threaded holes in the HB. Without threaded holes in the HB, how does the tool attach to it to pull it off?
                                 
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