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Thread tap sizes in block and heads

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    Thread tap sizes in block and heads

    I will hopefully soon start assembling the engine on our Stag. I would like to run a tap through all the threads in the engine to clean them up. Does anyone now what size and thread I need? Maybe it is best to buy a imperial kit?

    Also I saw mentioned that someone had tapped the piece between the engine and gearbox so it would be easier to undo in the future. Can anyone tell me the tap sizes and bolt lenghts needed for that also?
    Kirsti & Ian in Norway
    1973 Stag Mk2 (ex-USA), Mallard Blue, TV8 engine, Manual O/D

    #2
    An imperial set is what you need. No metric. Most are 5/16 and 3/8 UNC & UNF. If you look at the Torque Settings section of the ROM all the thread sizes are shown.
    Dave
    1974 Mk2, ZF Auto, 3.45 Diff, Datsun Driveshafts. Stag owner/maintainer since 1989.

    Comment


      #3
      It was me who taps the gearbox adaptor plate. The thread is 3/8 UNC the same as the exhaust manifold to cylinder head bolts.

      I just ordered a set of Stainless Stag exhaust manifold bolts from some ebay supplier and used those for the gearbox, there were more than I needed for the job, but I am always needing new bolts anyway.

      Neil
      Neil
      TV8, efi, fast road cams and home built manifolds. 246bhp 220lbft torque

      Comment


        #4
        .... and be wary of buying an all-singing and dancing kit where money has been saved on the material quality! A snapped tap-in-a-hole can really rain on your parade. I've got some basic grips and chucks, but order individual taps and dies from a good source like Chronos in St.Albans (although I think they've moved to Luton or Dinstable now)

        Drew
        The answer isn't 42, it's 1/137

        Comment


          #5
          Another very good supplier is Tracy tools. www.tracytools.com
          If you are only cleaning up existing tapped holes then you need only buy a plug tap. If you tap the plate for the gearbox mounting then you will need a first and probably a second tap but no plug tap. I alway recommend hss rather than the cheaper carbon for cutting threads in steel. Carbon is ok for aluminium alloys.
          John
          1978 Stag Brooklands Green

          Comment


            #6
            Thank you guys! I found a kit local that has the sizes we need. I am amazed to see the amount of crud that came out of the head stud holes after refreshing the threads.

            I have ordered the SS exhaust bolts and will tap the holes when they arrive.
            Kirsti & Ian in Norway
            1973 Stag Mk2 (ex-USA), Mallard Blue, TV8 engine, Manual O/D

            Comment


              #7
              Regarding the gearbox adaptor plate: I looked up some pictures of Stag engines with gearbox and was surprised to see that all of them had bolts with nuts. My car already came with a threaded steel bar, see attached pictures. I suspect this has been constructed by the PO to make removal easier? 274F412F-4B03-44EF-AF62-35694D94FA0D.jpegimage_41678.jpg
              Last edited by Ian928; 14 May 2020, 12:28.
              Kirsti & Ian in Norway
              1973 Stag Mk2 (ex-USA), Mallard Blue, TV8 engine, Manual O/D

              Comment


                #8
                Originally posted by Ian928 View Post
                Regarding the gearbox adaptor plate: I looked up some pictures of Stag engines with gearbox and was surprised to see that all of them had bolts with nuts. My car already came with a threaded steel bar, see attached pictures. I suspect this has been constructed by the PO to make removal easier? 274F412F-4B03-44EF-AF62-35694D94FA0D.jpeg
                That's cool.

                Comment


                  #9
                  You many want to invest in one of these. They clean out threads and not cut new threads.

                  https://www.amazon.com/2581-restaura...9387247&sr=8-5

                  To get to you your bolt size question. The head bolts and stud size is 7/16x14

                  Sujit

                  Comment


                    #10
                    Originally posted by sujitroy View Post

                    That's cool.
                    Is this of interest to someone? I can send these pictures to Chris Spain / Stagweber, he has done a small business of nice to have upgrades to the Stag. I can tell you that I can not produce it at a reasonable price here in Norway, but maybe someone else can.
                    Kirsti & Ian in Norway
                    1973 Stag Mk2 (ex-USA), Mallard Blue, TV8 engine, Manual O/D

                    Comment


                      #11
                      Originally posted by sujitroy View Post
                      You many want to invest in one of these. They clean out threads and not cut new threads.

                      https://www.amazon.com/2581-restaura...9387247&sr=8-5

                      To get to you your bolt size question. The head bolts and stud size is 7/16x14

                      Sujit
                      Thank you Sujit, I have something like that for the ignition plugs. I used a standard cutting thread for the block, it turned out good, no damaged threads.
                      Kirsti & Ian in Norway
                      1973 Stag Mk2 (ex-USA), Mallard Blue, TV8 engine, Manual O/D

                      Comment


                        #12
                        Remember you can put a couple of junior hacksaw cuts at an angle on an old bolt,that you are not re using,and use that to clean your threads.
                        Ken

                        Comment


                          #13
                          Originally posted by flying farmer View Post
                          It was me who taps the gearbox adaptor plate. The thread is 3/8 UNC the same as the exhaust manifold to cylinder head bolts.

                          I just ordered a set of Stainless Stag exhaust manifold bolts from some ebay supplier and used those for the gearbox, there were more than I needed for the job, but I am always needing new bolts anyway.

                          Neil
                          Neil,

                          Do you need to open up the holes in the gearbox for these bolts?

                          Terry
                          Terry Hunt, Wilmington Delaware

                          www.terryhunt.co.uk

                          Comment


                            #14
                            Chris Spain will look into the threaded rod. It must be possible to fit with engine in car or else the Flying Farmer solution is better I think. I have not tried if it really is possible to fit without removing the car, but I think it looks plausible, after all it has the perfect radius to just slide around the adapter.
                            Kirsti & Ian in Norway
                            1973 Stag Mk2 (ex-USA), Mallard Blue, TV8 engine, Manual O/D

                            Comment


                              #15
                              Originally posted by flying farmer View Post
                              It was me who taps the gearbox adaptor plate. The thread is 3/8 UNC the same as the exhaust manifold to cylinder head bolts.

                              I just ordered a set of Stainless Stag exhaust manifold bolts from some ebay supplier and used those for the gearbox, there were more than I needed for the job, but I am always needing new bolts anyway.

                              Neil
                              Do you just tap the aluminum adapter plate or use helicoils in it?
                              John

                              Comment

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