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Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

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  • Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    I pulled the heads off my 1991 Mercruiser 454 (a.k.a. 7.4L) yesterday. The pistons/cylinders look pretty good, Head gaskets were good, There was some rust on the exhaust ports of the heads on cylinders #4 & #5. Also some rust in the exhaust manifolds of ports #3,#5 & #4,#6. Pics below.

    Engine history=540 hours total over the course of 20 years. Moored seasonally in salt water.

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    I believe that Cylinders #4 & #5 share an exhaust cross-over port in the intake manifold to help with cold starts (?) (funky square port in the middle of the row of intake ports on the head). Anyway, this area of the intake manifold had serious rust on it when I took the intake manifold off. I am thinking that this was the source of water intrusion into the area of the exhaust ports on the middle cylinders.

    What do you all think? I hope the pictures are helpful.

    I am wondering if this is a typical problem with the 454's of that vintage (Mark IV, 1991). The way the intake manifold meets the cylinder head in that area does not seem to insure a good seal, and would allow the gasket to de-laminate over time.

    BTW - I leak tested both exhaust manifolds, and they are fine. So I am thinking the water is from the crossover port.

    Next steps are to take the valves out of the heads and get a look at the seats. I also have to get the engine mounted on an engine stand so I can have a peek at the lower end.
    Best regards,
    Formula 330 Sun Sport
    Twin Mercruiser 7.4 LX MPI (0F802036, 0F802039), Bravo 3's (0F806198, 0F806199)
    1969 Mercury 7.5 HP Outboard (26346XX)
    My F-330 Web Site: http://home.comcast.net/~tpenfield/F...30SS/Home.html
    My F-242 Web Site: http://home.comcast.net/~tpenfield/W...Boat_Page.html
    Member of the Month - February 2013
    http://www.iboats.com/blog/tpenfield...-of-the-month/


  • #2
    Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

    Anyway, this area of the intake manifold had serious rust on it when I took the intake manifold off. I am thinking that this was the source of water intrusion into the area of the exhaust ports on the middle cylinders.
    Ayuh,... That's an Exhaust passage, not water....

    I'd sooner think the riser gaskets were leakin'...
    I think I see rust near 'em in the 1st picture...
    A pic of the exhaust manifold from the top, instead of from the motor side maybe,..??
    Any Grease is Better,..... Than No Grease at All.......

    Comment



    • #3
      Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

      Originally posted by Bond-o View Post

      I'd sooner think the riser gaskets were leakin'...
      I think I see rust near 'em in the 1st picture...
      A pic of the exhaust manifold from the top, instead of from the motor side maybe,..??
      Here is a picture from the top of the manifolds. I'm not sure it is going to show much. The mating surfaces are OK, but come to think of it, a few years back, I did replace the gaskets. It could have been an issue left over from the old gaskets.

      Click image for larger version

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      Best regards,
      Formula 330 Sun Sport
      Twin Mercruiser 7.4 LX MPI (0F802036, 0F802039), Bravo 3's (0F806198, 0F806199)
      1969 Mercury 7.5 HP Outboard (26346XX)
      My F-330 Web Site: http://home.comcast.net/~tpenfield/F...30SS/Home.html
      My F-242 Web Site: http://home.comcast.net/~tpenfield/W...Boat_Page.html
      Member of the Month - February 2013
      http://www.iboats.com/blog/tpenfield...-of-the-month/

      Comment



      • #4
        Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

        Ayuh,... The exhaust passages are Rusty,...
        That water got in there, Somehow, Some way...
        Any Grease is Better,..... Than No Grease at All.......

        Comment



        • #5
          Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

          From those pictures, the manifolds are junk. The gasket surface (especially on the upper one) is gone. The surface between the exhaust passage and the water passage should be about 1/4" wide and clean shiny metal.
          Don S.

          sigpic

          Please, no PM's (Private Messages) regarding boat/engine problems.
          That is what the forums are for.
          Only forum/moderator issues will be answered in PM's.

          Comment



          • #6
            Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

            Looks like maybe both of those manifold -riser surfaces were leaking.

            If you had a friend with a vertical mill in his home shop you could probably mill all (4) surfaces and get some more life out of them.

            Taking them to a machine shop and having them "chuck them up" on a mill, might approach 1/2-3/4 or more of the cost of buying new when it's all said and done......... and you'd probably want to do all the flat surfaces (ex ports)....... but you'd still have old manifolds and risers with unknown levels of internal rust.


            I would just replace them.

            Sure would be nice if Dry-Joint manifolds and risers were available for the 454......that solves the riser gasket problem once and for all........but I don't think they're available at all for the 454. (good reason to go to a 496!)


            Regards,


            Rick
            ----------------------------------------------------------------------------------
            I use xxx oil and have never had a problem........
            This post was created with OpenSuSE x64 Linux!

            Comment



            • #7
              Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

              Taking them to a machine shop and having them "chuck them up" on a mill, might approach 1/2-3/4 or more of the cost of buying new when it's all said and done......... and you'd probably want to do all the flat surfaces (ex ports).......
              Ayuh,... At My local Machine Shop, they've got a HUGE flat-top belt-sander....
              He turns it on, 'n sets the part, by hand, onto the table for a few seconds, 'n then looks to see the results, continuing til he's satisfied...
              I watched 'im do a set of risers for me,...

              A big vise, 'n a large flat file can be used to some degree of success, dependin' on the operator of the file....
              Any Grease is Better,..... Than No Grease at All.......

              Comment



              • #8
                Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

                Looking at the block and heads, all your cooling passages (especially on the heads) are just about plugged closed. Ya got some work to do on her. Manifolds do look a bit "aged" and could probably stand to be replaced too.
                '92 Chaparral 2550 SX Sport
                454 BBC Mercruiser Bravo 1
                Tow with '04 F150 Larriat SuperCab 4x4 5.4 Triton
                US Coast Guard Aux.

                Comment



                • #9
                  Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

                  Originally posted by 04fxdwgi View Post
                  Looking at the block and heads, all your cooling passages (especially on the heads) are just about plugged closed. Ya got some work to do on her. Manifolds do look a bit "aged" and could probably stand to be replaced too.
                  Engine and boat are 20 years old, I *could* replace everything . . . maybe I should just get a new boat
                  Best regards,
                  Formula 330 Sun Sport
                  Twin Mercruiser 7.4 LX MPI (0F802036, 0F802039), Bravo 3's (0F806198, 0F806199)
                  1969 Mercury 7.5 HP Outboard (26346XX)
                  My F-330 Web Site: http://home.comcast.net/~tpenfield/F...30SS/Home.html
                  My F-242 Web Site: http://home.comcast.net/~tpenfield/W...Boat_Page.html
                  Member of the Month - February 2013
                  http://www.iboats.com/blog/tpenfield...-of-the-month/

                  Comment



                  • #10
                    Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

                    Originally posted by Bond-o View Post
                    Ayuh,... At My local Machine Shop, they've got a HUGE flat-top belt-sander....
                    He turns it on, 'n sets the part, by hand, onto the table for a few seconds, 'n then looks to see the results, continuing til he's satisfied...
                    I watched 'im do a set of risers for me,...

                    A big vise, 'n a large flat file can be used to some degree of success, dependin' on the operator of the file....

                    Yeah. I did my old 460 OMC risers and manifolds using my bench type belt sander. but it's a TLAR method at best..... Next time I would mill them on the neighbors C&C mill.
                    ----------------------------------------------------------------------------------
                    I use xxx oil and have never had a problem........
                    This post was created with OpenSuSE x64 Linux!

                    Comment



                    • #11
                      Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

                      Originally posted by tpenfield View Post
                      Engine and boat are 20 years old, I *could* replace everything . . . maybe I should just get a new boat
                      Why were the heads yanked in the first place? Motor is already torn down so see no reason not to try to clean / flush her out on the cheap. That's the course I would take, especially if there were no other problems with her, but now is a perfect time to "refresh" the engine. Mine's 20 years old w/ almost 1300 hours on her and purs like a kitten (knock on wood). My manifolds have surface rust inside (normal) but no blockage at all after the season is done. Haven't pulled the heads, but if engine temp and manifolds are an indication, I'm not going to do till needed.

                      Mainifolds aren't really that expensive either, unless you opt for the high end exotic ones. I guess the secret is to flush everything that has raw water running thru it on regular basis (like after every run in crappy water). There are flushing set-ups out there that let you flush it while in the water (I built my own) and it's extra easy with the Bravo having the raw water pump running off the engine.

                      PS: If you are junking her, I'll take her off ya hands. Lots of life left in that classic boat.
                      '92 Chaparral 2550 SX Sport
                      454 BBC Mercruiser Bravo 1
                      Tow with '04 F150 Larriat SuperCab 4x4 5.4 Triton
                      US Coast Guard Aux.

                      Comment



                      • #12
                        Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

                        Originally posted by 04fxdwgi View Post
                        Why were the heads yanked in the first place? Motor is already torn down so see no reason not to try to clean / flush her out on the cheap. That's the course I would take, especially if there were no other problems with her, but now is a perfect time to "refresh" the engine. Mine's 20 years old w/ almost 1300 hours on her and purs like a kitten (knock on wood). My manifolds have surface rust inside (normal) but no blockage at all after the season is done. Haven't pulled the heads, but if engine temp and manifolds are an indication, I'm not going to do till needed.

                        Mainifolds aren't really that expensive either, unless you opt for the high end exotic ones. I guess the secret is to flush everything that has raw water running thru it on regular basis (like after every run in crappy water). There are flushing set-ups out there that let you flush it while in the water (I built my own) and it's extra easy with the Bravo having the raw water pump running off the engine.

                        PS: If you are junking her, I'll take her off ya hands. Lots of life left in that classic boat.
                        The heads were pulled off because Cylinders 3,5 and 4,6 were showing 35 - 50% leak on a cylinder leak test. It proved to be the valves - some intake and some exhaust. Once things were opened up, the manifold/riser issue was discovered. It definately effected the exhaust valve on #5. I have not torn down the other cylinder head yet.

                        My plan is to do a valve job and get things back together. The engine only has 540 hours, so it has got some good life left in it.

                        I am looking to sell the boat at some point and move onto a bigger boat. I'm not sure just when all that will happen.
                        Best regards,
                        Formula 330 Sun Sport
                        Twin Mercruiser 7.4 LX MPI (0F802036, 0F802039), Bravo 3's (0F806198, 0F806199)
                        1969 Mercury 7.5 HP Outboard (26346XX)
                        My F-330 Web Site: http://home.comcast.net/~tpenfield/F...30SS/Home.html
                        My F-242 Web Site: http://home.comcast.net/~tpenfield/W...Boat_Page.html
                        Member of the Month - February 2013
                        http://www.iboats.com/blog/tpenfield...-of-the-month/

                        Comment



                        • #13
                          Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

                          My plan is to do a valve job and get things back together. The engine only has 540 hours, so it has got some good life left in it.
                          Ayuh,... from yer pictures, 'n descriptions, I don't see any reason to go deeper...
                          Any Grease is Better,..... Than No Grease at All.......

                          Comment



                          • #14
                            Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

                            Originally posted by Bond-o View Post
                            Ayuh,... from yer pictures, 'n descriptions, I don't see any reason to go deeper...
                            If motor was still in boat, I would agree 100%. But since it's sitting on the floor already, why not pop off the pan, and plastigauge the bearings, replace the 20 year old timing chain cover and pan gaskets and seals, front and rear seals on the crank, check the timing cover / pan for any rust problems, clean out some of that scale in the cooling passage holes and check the timing chain. Put it all back together after a clean bill of health (or replace anything that is marginal) and paint her up like new. Getting motor out and back into boat is the hard part.
                            '92 Chaparral 2550 SX Sport
                            454 BBC Mercruiser Bravo 1
                            Tow with '04 F150 Larriat SuperCab 4x4 5.4 Triton
                            US Coast Guard Aux.

                            Comment



                            • #15
                              Re: Mercruiser 454 tear-down - pulled the heads off - rusty exhaust ports

                              That is a great idea, the last thing you need is to put it all back in and break a timing chain or find some kind of oil leak that was caused when the motor was out and seals where disturbed. agree 100%.

                              Originally posted by 04fxdwgi View Post
                              If motor was still in boat, I would agree 100%. But since it's sitting on the floor already, why not pop off the pan, and plastigauge the bearings, replace the 20 year old timing chain cover and pan gaskets and seals, front and rear seals on the crank, check the timing cover / pan for any rust problems, clean out some of that scale in the cooling passage holes and check the timing chain. Put it all back together after a clean bill of health (or replace anything that is marginal) and paint her up like new. Getting motor out and back into boat is the hard part.
                              2006 q6 ski fish
                              mercruiser offshore 21p 4 blade ss
                              4 barrel holley equipped
                              thru transom exhaust
                              vortec 5.0L 220hp? +
                              nauticus smart tabs sx
                              sigpic
                              1999 suburban k2500
                              4x4 L-29 454
                              ls-1 injectors
                              roller rockers
                              gibson headers
                              true duals
                              black bear tune

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