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A short video that may help explain Ignition TA, and how to check/set our TA #(39)s.-gctid395563

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    A short video that may help explain Ignition TA, and how to check/set our TA #(39)s.-gctid395563

    It can sometimes be difficult to understand, so thought that you may enjoy this you tube video that I believe is sponsored by MSD.

    The main point behind my posting this, is to show just how easy it is to strobe our timing marks as we increase RPM, allowing us to see not only the progressive advance, but the RPM at which the progressive is Full-In, and stops advancing. Or in other words...., TA (total advance)!

    Unfortunately for us, these guys are doing a High Performance automotive engine, so the TA number will be quite different from what our goal is, but the procedure will be the same.

    There are many such videos out there, and it's tough to find one specific for Marine...., but this one appeared to be pretty darn good.

    Where the one man explains the 3 types of timing, we Marine Gear-Heads typically refer to these as BASE, Progressive (the curve) and TA (total advance).

    I would sooner explain these in this order:
    • Initial or BASE.... (idle)
    • Progressive.... (as seen in the form of a curve which takes us from BASE to TA, as RPM increases)
    • Total ...... (upon reaching the full-in rpm where the advance discontinues)




    A tad bit of clarity.

    He mentions that "Initial" is the total advance while the engine is at idle. Technically speaking, "Initial" is the advance seen at this RPM only, and is simply a result of where the distributor housing is positioned, and is always minus any Mechanical distributor advance (or EST for the Merc TB Igntion system guys).

    The engine used in this video is set up with a single timing pointer, whereas ours will have the timing tab with varying degrees and the large "V" notch.

    Our "V" notch is the same as their single pointer.

    Our harmonic balancer TDC marking, and any further balancer markings (degree decal), will be referenced against our "V" notch.

    Their harmonic balancer degree decal will be very similar to the ones that we can buy.

    NOTE: the balancer diameter determines which decal we purchase.

    Notice that with the full degree markings, they are NOT using a digitally advancing timing light.

    This is the "Real Degrees/Real Time" that I always refer to.

    A note of particular importance:

    At 3:20 min into the video, he begins to explain perhaps the most technical and critical portion of why ignition timing is so darn important.

    And that is....... LPCP.... (Location of Peak Cylinder Pressure)

    (do a Google search on this for more info)

    This is the mother load of Ignition Timing importance, so listen to what he has to say further into the topic.

    With exception to his explanation of LPCP being at 10* ATDC, he is dead on!

    (many engineers will prefer 12* to 14* ATDC.... a goal of 10* ATDC may detonate a Marine Engine.... not good!)

    None-the-less, our goal is to confirm and/or adjust the ignition advance as to achieve LPCP at the correct crankshaft angle.

    (he explains this nicely)

    NOTE: their TA numbers of 34* to 36* are for this High Performance automotive engine, and would very likely ruin our Marine engines.

    So we need to stay with our OEM numbers.

    After about 6:50 min into the video, it will no longer apply to our needs, but it's all good stuff to watch.

    Have fun with it!



    Regarding our mechanically advancing ignition distributors, any change to BASE or Initial, is an exact change to TA.

    IOW, if we advance BASE by 2*, we are also advancing TA by 2*, and visa-versa.

    Often we will need to "fudge" a bit on BASE advance in order to get the correct TA numbers that we want.

    If fudging a degree or two does the trick, it's not a deal breaker as long as our BASE advance does not exceed approximately 10* BTDC @ idle RPM, and/or does not fall below 6* (or so) BTDC @ idle RPM.

    However, if after checking this, and after not being able to acheive both the correct BASE advance and TA simultaneously, our ignition distributors will generally require being sent out to a shop for re-calibration via a Distributor Machine.

    Or, we simply replace it with new. Even so, we still perform the check as a safety measure.

    .
    Rick E. Gresham, Oregon
    2850 Bounty Sedan Flybridge model
    Twin 280 HP 5.7's w/ Closed Cooling
    Volvo Penta DuoProp Drives
    Kohler 4 CZ Gen Set

    #2
    Good stuff here! Bounty! Sticky for sure!

    Comment


      #3
      Yep - good stuff. Got that dvd when I purchased my MSD RTR marine distributor.

      MSD's are easy to set TAT and have about 21 different TAT combinations to suit almost any engine.

      I actually recommend these over the YLM type and standard types of distributors, especially if going into SBC or BBC.

      They are bulletproof and reliable. Just remember to use the MSD high vibration coil.

      Comment


        #4
        Jeff H wrote:
        MSD's are easy to set TAT and have about 21 different TAT combinations to suit almost any engine.
        I have no issues what-so-ever with people changing their own curves if they know precisely how to test afterwards.

        And this video does an excellent job at explaining that!

        But because many do not, I always recommend sending them out for this.

        A mere 1, 2 or 3 degree error at the distributor, is a 2, 4 or 6 degree error at the crankshaft!

        That may mean the difference between detontion, and no detonation.

        Study hard because there will be a test this coming Monday for those who are interested.

        Members with grades above 98% will receive a new Sea Ray decal set!

        These are first run decals.... not the seconds that we Bayliner owners usually receive.

        Members with grades at 100%, will get a look at the first run engines/drives that Sea Ray uses.

        No touch.... just a look at!

        .
        Rick E. Gresham, Oregon
        2850 Bounty Sedan Flybridge model
        Twin 280 HP 5.7's w/ Closed Cooling
        Volvo Penta DuoProp Drives
        Kohler 4 CZ Gen Set

        Comment


          #5
          That's why I said "easy to set" TAT, not "easy to find your TAT for your application"

          Comment


            #6
            Jeff H wrote:
            That's why I said "easy to set" TAT, not "easy to find your TAT for your application"
            Understood!

            Jeff, try finding the TA specs for any of the Chrysler Marine Corp engines! The guys over at ME.com have been searching for years now.

            The OEM service manuals simply offer BASE only..... nothing regarding the progressive or TA.

            .
            Rick E. Gresham, Oregon
            2850 Bounty Sedan Flybridge model
            Twin 280 HP 5.7's w/ Closed Cooling
            Volvo Penta DuoProp Drives
            Kohler 4 CZ Gen Set

            Comment


              #7
              I don't like Chrysler engines so no problem there!

              You remember me trying to find TA specs for my 383. No one wants to "speculate" on what it is, heck even the re builder did not want to give any type of info.

              I guess that's what I like about the MSD - you can look for "reasonable" specs and then semi apply them to your application, within reason.

              But still takes some testing, researching, etc.

              I remember the only advise you would give me was a "all in by this rpm" which actually lead me to a good couple sets of TAT specs that came with the distributor and then I fine tuned from there.

              I ended up with a ramp starting at about 1200 rpm, all in by 3200 rpm and a TAT of 31 on a quench built, low temp (155) 383 sbc (added this for anyone reading) and I get excellent performance and 2.1 mpg on a 2750. Can't beat that!

              Comment


                #8
                Jeff H wrote:
                • 1 wrote:
                • You remember me trying to find TA specs for my 383. No one wants to "speculate" on what it is, heck even the re builder did not want to give any type of info.
                • I guess that's what I like about the MSD - you can look for "reasonable" specs and then semi apply them to your application, within reason. But still takes some testing, researching, etc.
                • I remember the only advise you would give me was a "all in by this rpm" which actually lead me to a good couple sets of TAT specs that came with the distributor and then I fine tuned from there.
                • I ended up with a ramp starting at about 1200 rpm, all in by 3200 rpm and a TAT of 31 on a quench built, low temp (155) 383 sbc (added this for anyone reading) and I get excellent performance and 2.1 mpg on a 2750. Can't beat that!



                • 1 wrote:
                • Yes, I do recall that.

                  Seemed like it was tough to find specs for this engine in the Q/E build.
                • Yep!
                • I'm reluctant to post any numbers unless I knew the exact build, and it does make a difference.

                  If I do post any numbers, you can bet they'll be conservative.
                • I like it when the progressive begins no sooner than 1k rpm, and 3.2k rpm seems to be a safe number for Full-In.



                Rick E. Gresham, Oregon
                2850 Bounty Sedan Flybridge model
                Twin 280 HP 5.7's w/ Closed Cooling
                Volvo Penta DuoProp Drives
                Kohler 4 CZ Gen Set

                Comment


                  #9
                  Long as we're here, I'll add this;

                  TDC markings are only accurate if nothing has caused them to change over the years.

                  Outer balancer rings can slip on the inner hub (although rare on our Marine engines) and will cause our ignition timing to be off.

                  Timing chain cover "tabs" can also become damaged, and are no longer accurate.

                  To check this, there is only one means of doing this..... PPS method (i.e., positive piston stop).

                  You can find this information on the Internet pretty easily.

                  Timing decals or timing tape:

                  If you add a decal, you must know the balancer diameter, in order to purhcase the correct decal, or the numbers will not be accurate.

                  If you can't find a decal, or don't want to take the time, you can mark off your balancer simply by using geometry.

                  Find the OD of your balancer.

                  Draw an identical diameter circle on paper (we need to be using the same circumference dimension).

                  Using a degree wheel, divide this circle into a 30* wedge section....... or take it further, and divide it into increments of 5* up to 30* at the circumfrence.

                  Using an old school architect's compass, set the compress between the Zeor mark and the new 30* mark on your paper circle.

                  Lock the compress down.

                  Transfer this over to the balancer, beginning with one pointer in the TDC notch.

                  Scratch the new 30* mark towards Port from the TDC notch (std LH rotation engines only).

                  Make this 30* mark a bold one.

                  Now go back and set the compress for 5*, and again, sratch a new 5* mark towards Port, beginning with one pointer in the TDC notch.

                  Repeat this for 10*, 15*, 20*, 25* and so on, each beginning at the TDC notch.

                  If you have not yet assembled an engine, do this on the work bench, and make these degrees more permanent by cutting them into the balancer face.

                  You can highlite these with white paint.

                  Now as you strobe your timing marks, you will reference these degrees against the largest V notch in the time chain cover tab.

                  This will actually simplify your timing procedure for you.

                  Attached files [img]/media/kunena/attachments/vb/699835=29303-Degrees transfered to Harmonic Balancer.jpg[/img] [img]/media/kunena/attachments/vb/699835=29327-SBC TDC markings on Balancer.jpg[/img]
                  Rick E. Gresham, Oregon
                  2850 Bounty Sedan Flybridge model
                  Twin 280 HP 5.7's w/ Closed Cooling
                  Volvo Penta DuoProp Drives
                  Kohler 4 CZ Gen Set

                  Comment

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