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Changing a reverse rotating motor to a standard rotating motor.

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  • Changing a reverse rotating motor to a standard rotating motor.

    To make a long story short. Last yr I built this(Completed Boat Projects) I/O pontoon that has a 140hp 4cyl mercruiser, because Iím a guy who like to go fast and cant leave anything alone, and spends to much time search craigslist for deals.
    I ended up buying a 22ft celebrity with a cracked 305 sbc.

    The reason I bought it was to sell the trailer (Iím $800 ahead right now) strip all the accessories off of it and find another running 5.7l marine/truck motor. Since everyone likes to take things apart that you donít have to put back together here is my way of removing a motor.


    Fast forward to last night I find a guy on CL selling two house boat 5.7l SBC standard and reverse Rotation. Motors were out of the boats but still had the transmission and starters hooked up. After looking the motors over really well, pulling the plugs and doing a compression check. I determined that the standard rotation one was low on compression and one cylinder had rusty water in it (not good) the reverse rotation one check out great.
    Keep in mind this guy is telling me that itís a reverse rotation motor and the firing order on the intake is different then your standard 18436572 but both motors spin counterclockwise when looking at the back of the flywheel. HMMM
    Iím sitting here at work thinking, doing some reading and wondering what it would take to(assuming the reverse rotation motor is truly that) take the reverse rotation motor and make is spin standard.
    Can I pull the cam and timing gear off the standard rotation install it in the reverse rotation change the front/rear main seals and call it good? Do I even need to change the Cam and I just change from timing gear to a chain. I understand the pistons are different but Iím not worrying about that right now.
    I can get numbers off the motors tonight if need be. It was late last night and the wife wasnít exactly happy when I showed up with 2 motors. The good news is in less then a week my CI has gone up 24.


  • #2
    Re: Changing a reverse rotating motor to a standard rotating motor.

    Reverse rotation cams use a gear drive so the cam, distributor, and oil pump all turn in the standard direction. Therefore the standard distributor and oil pump are used. You must use a standard cam and timing chain set up. You absolutely will change front and rear crank seals or they WILL leak. Starter is an issue, and the drive on that engine if you are taking it too will have to be changed. Volvos are very easy to change for engine rotation. Quite frankly I'd keep looking.

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    • #3
      Re: Changing a reverse rotating motor to a standard rotating motor.

      I already bought the two motors, guy was basically giving them away. Two SBC with all running gear (minus transmission and outdrives) for 200 bucks. Hard to say no.

      My thought is take the cam, and timing chain assuming they measure correct and look good still and install them into the reverse motor making it a standard rotation motor.

      The thing I can figure out and will do more checking tonight is why both motors when hooked up to a battery would spin the same direction. I'm wondering/thinking that the motor are standard rotation and the reverese was done in the transmission. From my reading this is a standard practice.

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      • #4
        Re: Changing a reverse rotating motor to a standard rotating motor.

        Originally posted by TurboM700 View Post
        why both motors when hooked up to a battery would spin the same direction.
        Occam's razor says the simplest explanation is usually the correct one. That would be: If the starters spin both engines in the same direction (ccw at the flywheel) then they are both standard rotation. Now I believe (and I may be wrong) that both distributors would turn in the dame direction CW, so check the wiring on the distributors my quick research says 1-2-7-5-6-3-4-8 for the reverse rotation scb.
        Terry
        87, 4WINNS H 190
        470/Alpha I

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        • #5
          Re: Changing a reverse rotating motor to a standard rotating motor.

          I will check here in a few hrs but the first number on the manifold was 8 then 2. I suppose it possible that they put a Reverse rotation intake manifold on a standard engine.

          I guess I will pop the timing cover off tonight and see if there is gears or chain in there.

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          • #6
            Re: Changing a reverse rotating motor to a standard rotating motor.

            Originally posted by TurboM700 View Post
            I guess I will pop the timing cover off tonight and see if there is gears or chain in there.
            Easiest way to tell for sure.

            LK

            1997 Sea Ray Sundancer 250 5.7EFI / BIII

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            • #7
              Re: Changing a reverse rotating motor to a standard rotating motor.

              Looks like there both standard roatation motors. The numbers I was reading on the motor that I was TOLD was a reverse rotation motor were a GM part number for the intake. OOOPPS Got home and looked closer and they both have the same firing order stamped into the intake.

              Now lets hope atleast one of these motors turns out to be good. I started stripping parts off my 305 that had the cracked block and putting them on the 350 to see if I can get them to run.

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              • #8
                Re: Changing a reverse rotating motor to a standard rotating motor.

                Well there you go. Good luck keep us apprised!

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