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4.3 Mercruiser Distributor Mystery Solved

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  • 4.3 Mercruiser Distributor Mystery Solved

    Got my 1988 21' Chris Craft Scorpion 4.3L, Alpha one end of last season. Took the craft out 3 times ran fine. But I felt there was something a bit off.

    I have worked on automotive engines for years with success and have done just about everything. Learned alot about marine engines over the winter and I was determined to find out what was wrong with this engine.

    Before the winter came, I noticed that the spark plug wires were not going to the correct cylinders. I have heard all the talk on here (when I posted this problem before) That the numbers on the cap don"t matter and as long as you get the firing order right, the engine will run fine. Well maybe in certain situations, but NOT THIS ONE!

    I have changed many a distributor cap, rotor, wires and plugs in my day. But this was the first marine remanufactured engine that I have ever worked on where somebody screwed around with the distributor and the wires. The engine is the original MCM 175 that has been bored over .030 with all new internals. The mecanic did a OK job replacing the engine but one thing he did was very WRONG.

    This afternoon I got into my boat and ran a test that I have been dying to run all winter. From my studies over the winter I knew that the distributor was OUT OF PHASE with the Cam/Crank. Yes, out of phase. This is when the distributor gear is not set into proper mesh/timing with the cam drive gear when the engine is at TDC. I ran a test before I changed anything.

    I got the engine up to TDC. I made sure it was the compression stroke. Then I removed the distributor cap. Guess what? The rotor was INBETWEEN the #2 and #1 cap tower contacts! I always knew that the distributor base was twisted way too much to the starboard side. He did this to compensate for being off one or more gear teeth (remember, he had the wires going to wherever on the cap). But what he and many don't understand is that moving the distributor base to compensate for an incorrectly installed distributor will NOT correct the problem. You will still be MECHANICALLY OUT OF PHASE. Yeah, the engine will run, but not as designed. And not as smoothly as it could.

    I removed the distributor hold down clamp and synced the drive gear and the rotor over until they fell into the hole an the rotor was pointing right at the #1cylinder in the block. Made sure the distributor base/ (mounting boss for a module) was facing the carb straight-on. Locked down the Dizzy.

    Now, when you rotate the engine to TDC the rotor not only points to the #1 cylinder (a famous V block occurrence) But when you shine a mini maglite lightbeam on the #1 tower, hold it still, then remove the cap. The light beam shines right dead smack on to the rotor contact. A slight 1 to 5 Deg. turn may be needed when timing the engine but it will not be the 30 degree crank he had it set to before. (Not talking timing/BTDC here. Talking compensation for incorrect distributor install)

    I say again, it does matter how you drop in a distributor on these GM engines. By using this boat three times last season, I have proven that the engine will run OK when out of phase. But it will run sort of rough and also I foud out that it fouled all the plugs. The reason...not complete combustion from being OUT OF PHASE. The carb needed a rebuild as well, but this ignition problem was the main problem with this engine.

    I have always taken great care when working on any engine's ignition system. I have learned from this experience that many do not take the same care.

    CCJ
    sigpic
    1988 Chris Craft Scorpion
    4.3L V6 Mercruiser
    Alpha 1 Drive


  • #2
    Re: 4.3 Mercruiser Distributor Mystery Solved

    Re-posting
    sigpic
    1988 Chris Craft Scorpion
    4.3L V6 Mercruiser
    Alpha 1 Drive

    Comment



    • #3
      Re: 4.3 Mercruiser Distributor Mystery Solved

      If it is "out of phase" top and bottom - the plug won't know the difference.

      Immagine how nice it will run when you get the carb sorted out.

      Comment



      • #4
        Re: 4.3 Mercruiser Distributor Mystery Solved

        Congrats.
        You managed to solve a problem that never existed.
        The last time religion controlled the world it was known as the Dark Ages

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