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    Crack Inside Intake Manifolds

    Hi All,

    I removed the carbs on my stock 1991 NT650. I can now see into the intake manifold on both cylinders. I see two valves in both the front cylinder and rear cylinder. There is a ridge of cast aluminum between each pair of valves. Both the front and rear cylinders have a crack in this ridge that runs across the ridge from one intake valve recess to the other. The crack does NOT appear to extend down into the valve seats.

    That BOTH cylinders show this crack suggests that it is a common defect. Has anyone else seen the crack? Does the crack cause problems?

    Thanks!

    #2
    Is it a crack or a line in the casting?

    If you were looking for a support group you're barking up the wrong tree. This place is fulla enablers dude. - Shooter77us

    The bitterness of low quality lingers long after the thrill of a low price has gone. - RacerX450

    Comment


      #3
      Originally Posted by ParcNHawk View Post
      Is it a crack or a line in the casting?
      ^^^^^^^
      that

      Have pics?
      Don't spend money and buy, spend time and learn.

      Comment


        #4
        Yes, a crack for sure. Visible in both intake manifolds. Crack seems harmless enough since it appears NOT to penetrate into the valve seat area. Intake Manifold Crack.png

        Comment


          #5
          WOW, looks like a casting flaw. How many miles? Sorry I don't have a solution, but seems concerning to me.

          Comment


            #6
            Originally Posted by mhead View Post
            Yes, a crack for sure. Visible in both intake manifolds. Crack seems harmless enough since it appears NOT to penetrate into the valve seat area. Intake Manifold Crack.png
            H.mm...

            I don't have a set of heads here, also don't remember seeing that. It's strange it would be on both.

            In times like this it's always best to lean on your higher power.


            Hordpower to be more specific and less AA.
            Don't spend money and buy, spend time and learn.

            Comment


              #7
              Parting line/shift in the casting. All Hawks have it, some worse than others. Not a crack. Well, 99.9999% not a crack, I've never seen a true crack there, but this one is particularly bad. Usually disappears when ported.
              J.D. Hord
              Keeper of Engine Nomenclature, 9th Order

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                #8
                Hordpower;n963745. Usually disappears when ported.
                and there it is..
                Don't you love it when the solution comes with an added benefit. Hehe
                Don't spend money and buy, spend time and learn.

                Comment


                  #9
                  If there ever was an excuse needed to port your heads...

                  Comment


                    #10
                    Makes you wonder if in 1991 they were just running the program on fumes and gave zero Ef's about the Hawk production or something?
                    88 Blue Hawk GT - Under construction but rideable (guest approved)
                    89 BlackHawk 2.0 - On the lift and being assembled
                    90 Hawk GT (color as to yet be determined) - Still on the shelf in crates

                    Comment


                      #11
                      Well, the 1991 heads were a different casting than 88-90. So things should have been better.

                      Originally Posted by rpcraft View Post
                      Makes you wonder if in 1991 they were just running the program on fumes and gave zero Ef's about the Hawk production or something?
                      J.D. Hord
                      Keeper of Engine Nomenclature, 9th Order

                      Comment


                        #12
                        Hordpower.. after prodding with a dental pick it seems the "crack" doesn't go much below the surface. My guess is that this is a flow meet-up. I have experience with plastic injection molding. Slight lines sometimes appear in molded parts when the melted plastic arrives at a point from two directions. So two -surfaces- meet and sometimes don't want to flow together slightly which leaves a line. Maybe this effect can explain the "crack" The "crack" does have a nasty offset look to it however.

                        In any event I believe the valve seats are un-cracked since if cracked I'm sure the engine would complain and the intake port would be carbonized. Major problems.

                        So I'm going to ignore this feature and put my carbs back on. I'll be happy if I can just get the Hawk running again.
                        Thanks for ideas and advice.

                        Comment


                          #13
                          Originally Posted by mhead View Post
                          Hordpower.. after prodding with a dental pick it seems the "crack" doesn't go much below the surface. My guess is that this is a flow meet-up. I have experience with plastic injection molding. Slight lines sometimes appear in molded parts when the melted plastic arrives at a point from two directions. So two -surfaces- meet and sometimes don't want to flow together slightly which leaves a line. Maybe this effect can explain the "crack" The "crack" does have a nasty offset look to it however.

                          In any event I believe the valve seats are un-cracked since if cracked I'm sure the engine would complain and the intake port would be carbonized. Major problems.

                          So I'm going to ignore this feature and put my carbs back on. I'll be happy if I can just get the Hawk running again.
                          Thanks for ideas and advice.
                          It's hard to not be able to get a Hawk running. if it is just dirty and in need of intake boots and carbs rebuilt it should go.
                          88 Blue Hawk GT - Under construction but rideable (guest approved)
                          89 BlackHawk 2.0 - On the lift and being assembled
                          90 Hawk GT (color as to yet be determined) - Still on the shelf in crates

                          Comment


                            #14
                            I checked my Mark2
                            The rear is clean and the front has a parting line
                            Doesn't seem like crack

                            rear.jpg

                            front.jpg

                            mk2.jpg

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