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Engine Timing - 20 degrees BTDC

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  • Engine Timing - 20 degrees BTDC

    So my boat was idling a bit rough and running a little rich. Checked timing and it was at 20 degrees instead of around 10. Loosened up the nut and tried to turn the distributor and might as well have been trying to free Excalibur. Sprayed some Aero Kroil along the base of the distributor. Any idea if that will help or do I need to order a new distributor and jackhammer the old one out.

    89 Prostar 351. Original distributor.

  • #2
    This can suck. It's usually the o ring that has hardened and sometimes fallen apart jamming up the shaft.

    I spent an entire afternoon pulling one from a 356 pre A and usually it means something like a strap wrench and wiggle spray wiggle spray wiggle pull over and over.

    If you can find a way to apply upwards pressure it helps.

    But as a thought experiment how is your points gap? If your points have worn or the plastic wear surface wears the gap changes and this causes timing to shift.

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    • #3
      good luck

      .
      Last edited by waterlogged882; 06-01-2021, 07:24 PM.
      93 190
      (safe click)

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      • #4
        Originally posted by 88 PS190 View Post
        This can suck. It's usually the o ring that has hardened and sometimes fallen apart jamming up the shaft.

        I spent an entire afternoon pulling one from a 356 pre A and usually it means something like a strap wrench and wiggle spray wiggle spray wiggle pull over and over.

        If you can find a way to apply upwards pressure it helps.

        But as a thought experiment how is your points gap? If your points have worn or the plastic wear surface wears the gap changes and this causes timing to shift.
        EI...

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        • #5
          Originally posted by stuartmcnair View Post
          EI...
          So has it just been -20 since install? In which case has it always run poorly?

          You need to get it to turn before you can come out with it.

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          • #6
            No. This is a new "this year" thing (every year there is a "this year" thing). What I decided to do after speaking with a pretty good marine mechanic is to try and loosen up the distributor and see if I can get it to turn. Told me to take a small pipe wrench to it. Scares me but if it breaks, it breaks. If that makes it where I can get the timing right I will still order a new distributor just because it's probably time anyway.

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            • #7
              I am interested as to how the distributor is seized at -20. If it was set at the prescribed -10 originally and ran fine last year then there may be something much bigger at play for it to have both shifted 10 degrees and now seized?

              I would be starting from the assumption that the distributor may actually be stuck at -10 and that replacing your points, cap and rotor as per normal servicing may return your timing to normal and fix the rough running? If you are planning to replace it all anyway there is no harm in trying this before creating more work.

              Just my 2c...
              Cheers

              Mark

              '99 Mastercraft ProStar 205 330-LTR

              Comment


              • #8
                I'd check that the timing mark on the crankshaft pully is actually correct. 20deg btdc is pretty close to not running/idling at all, then, under load, you'd know if it's that far advanced (pinking/predetonation)

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                • #9
                  Originally posted by stuartmcnair View Post
                  What I decided to do after speaking with a pretty good marine mechanic is to try and loosen up the distributor and see if I can get it to turn. Told me to take a small pipe wrench to it. Scares me but if it breaks, it breaks.
                  Start with a strap wrench if you have one. The pipe wrenches can squeeze a bit and if you can get it moving even a little you can wiggle it up and out. But if it only wiggles a tiny bit plan on working on this for hours so wear a hat

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                  • #10
                    Originally posted by chrislandy View Post
                    I'd check that the timing mark on the crankshaft pully is actually correct. 20deg btdc is pretty close to not running/idling at all, then, under load, you'd know if it's that far advanced (pinking/predetonation)
                    This is a solid idea. Harmonic balancers can slip...not common but it does happen.

                    Comment


                    • #11
                      Originally posted by d2jp View Post
                      This is a solid idea. Harmonic balancers can slip...not common but it does happen.
                      Agree on changing the points etc. If the harmonic balancer is keyed on the crank how can it slip? Asking for a friend

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                      • #12
                        Originally posted by Bouyhead View Post
                        Agree on changing the points etc. If the harmonic balancer is keyed on the crank how can it slip? Asking for a friend
                        Rubber between balancer and keyed shaft allows outer ring to slip.

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                        • #13
                          Originally posted by Mark rsa2au View Post
                          I am interested as to how the distributor is seized at -20. If it was set at the prescribed -10 originally and ran fine last year then there may be something much bigger at play for it to have both shifted 10 degrees and now seized?

                          I would be starting from the assumption that the distributor may actually be stuck at -10 and that replacing your points, cap and rotor as per normal servicing may return your timing to normal and fix the rough running? If you are planning to replace it all anyway there is no harm in trying this before creating more work.

                          Just my 2c...
                          No idea. Still advances and retards with the throttle. Just doesn't return to 10. Boat runs absolutely fine at throttle. Just not idling worth a damn. I may be hunting snipe but I have time.

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                          • #14
                            Originally posted by stuartmcnair View Post
                            No idea. Still advances and retards with the throttle. Just doesn't return to 10. Boat runs absolutely fine at throttle. Just not idling worth a damn. I may be hunting snipe but I have time.
                            If it runs fine under load then it is definitely not running at 45+deg btdc! (assuming typical around 25deg advance on the initial 10deg (35 total))

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                            • #15
                              Originally posted by chrislandy View Post
                              If it runs fine under load then it is definitely not running at 45+deg btdc! (assuming typical around 25deg advance on the initial 10deg (35 total))
                              Got it back to 10 but will only advance another 10 degrees or so. Ordered a new distributor.

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