exhaust leak?

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  • CRUX
    Senior Member
    • Nov 2019
    • 40

    exhaust leak?

    Hi All,

    I seem to have an exhaust leak. From my inspection it seems to be coming from the top/stern edge of the valve cover (directly below the exhaust manifold). It is a slight whisp. Attached is 2 screenshots showing where it is coming from, along with a (very poor) video at the link attached. . You can see the whisp of smoke more clearly at 20 seconds in the video.

    I Just replaced the black iron pipe to the waterlift muffler during this past winter and it doesn't appear to be coming from that.

    I will inspect further, but just looking for some ideas from the crew here in regards to the likely area it is coming from...bad head, hole in the block, bad gasket in valve cover?

    As always, thank you!

  • CRUX
    Senior Member
    • Nov 2019
    • 40

    #2

    Comment

    • hanleyclifford
      Afourian MVP
      • Mar 2010
      • 7032

      #3
      Looks like a blown manifold gasket.

      Comment

      • joe_db
        Afourian MVP
        • May 2009
        • 4544

        #4
        If it actually is coming out of the valve cover, it is blow-by, not exhaust. It is more likely a leak at the manifold aiming down there. I would run the engine and pour a little Marvel Mystery Oil into the carb. This will make thick exhaust smoke and should make any leaks much more obvious
        Joe Della Barba
        Coquina
        C&C 35 MK I
        Maryland USA

        Comment

        • CRUX
          Senior Member
          • Nov 2019
          • 40

          #5
          Thanks, I'll try the MMO trick. Do you mean literally pour some into the mouth of the carb?

          I've been hitting the three large studs on the manifold with some KROiL all weekend, and just ordered some gaskets. Will try to pull the manifold next week.

          I'm sure there are different perspectives on this, but I've used Pematex Ultra Copper High Temp on other areas of the exhaust, would using this in combination with the Moyer gasket be ok?

          Comment

          • Dave Neptune
            Afourian MVP, Professor Emeritus
            • Jan 2007
            • 5117

            #6
            Yes just dump a tiny bit into the carb, it will cause the engine to smoke and the smoke may make the area of the leak easier to detect. Another easier way is just use an oil spray while running as it is just a cleaner process and it will smoke too.

            RE sealing the manifold I personally recommend the Permatex Av grade or the #2. It will "stick" to the old oily block much better. All of the silicone based sealer are primarily designed for aluminum as the aluminum will not absorb oil like the cast iron. The ability of the cast iron to absorb oil is makes it such a good material for engines BUT the oil in the cast iron also will not allow the silicone to adhere due to the oil. The Av grade and the #2 Permatex are oil based and will stick forever. The silicone is superior on aluminum parts and the Permatex Av and the #2 work just as well.

            Dave Neptune

            Comment

            • joe_db
              Afourian MVP
              • May 2009
              • 4544

              #7
              If the stud comes out of the block instead of the nut off of the stud, be aware that the stud goes into a coolant passage and will leak if not sealed when you put it back.
              Joe Della Barba
              Coquina
              C&C 35 MK I
              Maryland USA

              Comment

              • hanleyclifford
                Afourian MVP
                • Mar 2010
                • 7032

                #8
                Whenever I do a manifold gasket I remove the studs and check them for number of good threads. I like a minimum of 4. Better yet, just replace all the studs. As Joe mentioned those studs go into water passages and if you have raw water cooling it's a good bet they will all be kaput. Before installing the studs (new or old) run a tap into the block to refresh the threads, then install the studs using Permatex #2. If you are using old studs run a die over the threads (3/8 x 24). Use light machine oil on the fine threads before assembly. I do not use any gasket sealer in this procedure. Of far greater importance is meticulous cleaning of all mating surfaces. Build your torque to 35 ft lbs in 10 lb increments.

                Comment

                • joe_db
                  Afourian MVP
                  • May 2009
                  • 4544

                  #9
                  Another warning - if the block itself is corroded and you remove the studs, you can have a first-class mess on your hands if the threads strip out.
                  Joe Della Barba
                  Coquina
                  C&C 35 MK I
                  Maryland USA

                  Comment

                  • CRUX
                    Senior Member
                    • Nov 2019
                    • 40

                    #10
                    Alright, if that's the case, I'll make sure to re-seat the studs with some JB weld.

                    Comment

                    • Dave Neptune
                      Afourian MVP, Professor Emeritus
                      • Jan 2007
                      • 5117

                      #11
                      Careful using JB on studs. Unless you are aligned perfectly or torqueing up before the JB has set you risk it cracking and then no seal. Yes it can help hold a bit but it is a temporary patch. If the threads are OK the Permatex #2 works far better. It does not add strength but it remains pliable for a good seal which lasts and that is what you need in the water jacket.

                      Dave Neptune

                      Comment

                      • CRUX
                        Senior Member
                        • Nov 2019
                        • 40

                        #12
                        Joe_db, If that were the case and the threads strip out. Would the solution be to drill and tap to a larger diameter stud (1/2"?) ?

                        Thanks!

                        Comment

                        • hanleyclifford
                          Afourian MVP
                          • Mar 2010
                          • 7032

                          #13
                          [QUOTE=CRUX;n219316]Joe_db, If that were the case and the threads strip out. Would the solution be to drill and tap to a larger diameter stud (1/2"?) ?

                          Thanks! [/QUOT Moyer Marine sells repair stud kits for this very purpose. I do not like JB Weld in this application.

                          Comment

                          • joe_db
                            Afourian MVP
                            • May 2009
                            • 4544

                            #14
                            Originally posted by CRUX View Post
                            Joe_db, If that were the case and the threads strip out. Would the solution be to drill and tap to a larger diameter stud (1/2"?) ?

                            Thanks!
                            My solution ended up being a new engine. If the metal is not too far gone, the repair kit will work. In my case even that didn't last, the block was badly corroded. Do not leave it leaking, even a very slow leak is removing iron from the engine around the studs bit by bit.
                            Joe Della Barba
                            Coquina
                            C&C 35 MK I
                            Maryland USA

                            Comment

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