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  • random find, Offy build pictorial

    Probably old hat for lots of folks here, but I have never seen the internals of an Offy in such detail.

    https://www.hotrod.com/articles/asse...r-engine-step/

    The crank bearing/web assembly, wow! No wonder this engine was so tough and had such longevity in the sport.

    Quite a lot different than building up a V8.

  • #2
    A question for knowledgeable Offy guys.

    In about the 16th photo they say the valve lash is .0016" and .0018" for intake and exhaust, respectively.
    My work involves precision manufacturing, but not engines.

    Is that dimension correct?
    Perhaps off by a decimal place.

    Reason I ask, the feeler shim that guy is using looks thicker.

    Comment


    • #3
      Originally posted by mike_c_56 View Post
      A


      Perhaps off by a decimal place.
      Yup. Intake clearance is .016" and exhaust is .018". Those are actually somewhat common valve clearances for quite a few engines.

      The thing people don't realize about Offenhausers is that there were many variations on how to build them. And the barrel crankcase was both a strength and a weakness. Yes, the bottom end was tough but unlike today's precise computer controlled machining all of those big castings were machined by hand as were the bearing webs that determined oiling clearances. And Offy cranks were oiled from the bottom which called for heavy weight oils and incredibly high oil pressures when the turbocharged versions came along. You were looking at up to 150 PSI pressures hot. When the Cosworths came along with their top oiling crankshafts old Offy mechanics couldn't believe that they would live running at only 70 PSI. And the Cosworths (and later race engines) employed precision machining which pretty much did away with any need for a barrel single piece crankcase.

      Offy mechanics all put things together in their own way. Some mechanics built powerful engines that lasted for multiple races while others had engines that failed early on. There were a ton of tricks that engine builders mostly kept to themselves.
      Last edited by indyrjc; 05-03-2020, 07:05 PM.

      Comment


      • #4
        Originally posted by indyrjc View Post

        Yup. Intake clearance is .016" and exhaust is .018". Those are actually somewhat common valve clearances for quite a few engines.
        Thanks. I'll not complain about that.

        I think it was pretty good find of motor-head click bait.

        Comment


        • #5
          Originally posted by indyrjc View Post

          Yup. Intake clearance is .016" and exhaust is .018". Those are actually somewhat common valve clearances for quite a few engines.

          The thing people don't realize about Offenhausers is that there were many variations on how to build them. And the barrel crankcase was both a strength and a weakness. Yes, the bottom end was tough but unlike today's precise computer controlled machining all of those big castings were machined by hand as were the bearing webs that determined oiling clearances. And Offy cranks were oiled from the bottom which called for heavy weight oils and incredibly high oil pressures when the turbocharged versions came along. You were looking at up to 150 PSI pressures hot. When the Cosworths came along with their top oiling crankshafts old Offy mechanics couldn't believe that they would live running at only 70 PSI. And the Cosworths (and later race engines) employed precision machining which pretty much did away with any need for a barrel single piece crankcase.

          Offy mechanics all put things together in their own way. Some mechanics built powerful engines that lasted for multiple races while others had engines that failed early on. There were a ton of tricks that engine builders mostly kept to themselves.
          The crankcase looked pretty substantial but I was surprised that it had a trunnion attaching it to the chassis instead of a solid mount.
          Their concern was chassis flex would deflect the crankcase? Yikes!!

          Comment


          • #6
            Somewhere I thought I had the procedure for firing up an Offy, and it looked fairly complex. I'll have to see if I still have it.
            "For in the final analysis, our most basic common link is that we all inhabit this small planet. We all breathe the same air, we all cherish our children's future, and we are all mortal".

            John Kennedy at American University 1963

            "Nearly all men can stand adversity, but if you want to test a man's character, give him power"

            A. Lincoln

            Comment


            • #7
              I think I remember that the engine had different spark plugs? One set for "cold start", and another set for running?

              Anyone know of this? That may have been common to engines (or spark plugs) of and era, not just a manufacturer.

              Comment


              • #8
                Originally posted by Belanger99 View Post
                Somewhere I thought I had the procedure for firing up an Offy, and it looked fairly complex. I'll have to see if I still have it.
                Here you go...
                You've worked so hard on the kidney. Very special -- the kidney has a very special place in the heart. It's an incredible thing. Donald John Trump

                Brian's Wish * Jason Foundation

                Comment


                • #9
                  Originally posted by Jamski View Post
                  Thanks, I couldn't find it.....Reading that always made me wonder about the guys who ran them at vintage events, it looked easier to launch the Space Shuttle than to fire up an Offy. I've often wondered if starting the Novi was as complex.
                  "For in the final analysis, our most basic common link is that we all inhabit this small planet. We all breathe the same air, we all cherish our children's future, and we are all mortal".

                  John Kennedy at American University 1963

                  "Nearly all men can stand adversity, but if you want to test a man's character, give him power"

                  A. Lincoln

                  Comment

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