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You need to know your engine rotation when ordering parts or performing some repairs.

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Steps

  1. Determine Your Mercruiser Engine Rotation Step 1.jpg
    1
    Locate your engine serial number.
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  2. Determine Your Mercruiser Engine Rotation Step 2.jpg
    2
    Contact an online help-site such as sterndrive-information.com to get your engine rotation.
  3. Determine Your Mercruiser Engine Rotation Step 3.jpg
    3
    Look for original factory specification decals which might designate the engine rotation.
  4. Determine Your Mercruiser Engine Rotation Step 4.jpg
    4
    Observe the rotation of the engine cranking or running if possible.
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Tips

  • Right Hand Engines (RH) are reverse rotation. Also known as Clockwise Rotation (CR).
  • Most Mercruiser LH standard rotation engines use a timing chain whereas RH reverse rotation engines use only timing gears.
  • Do not confuse engine rotation with prop rotation. They might not (and usually are not) the same.
  • RH and LH engines have different timing specs.
  • The distributor shaft rotation is the same for RH and LH motors and it is usually almost always a distributor shaft right hand rotation as viewed from above.
  • All Mercruiser Sterndrive engines are LH rotation.
  • Use care when using a variable timing light as it must be set to zero when timing a reverse rotation engine.
  • Usually only older twin inboard powered vessels have one engine RH reverse rotation.
  • Some Mercruiser Inboard (NOT sterndrive) engines can be RH rotation.
  • Engine rotation is determined by looking from the flywheel end towards the pulley end.
  • Some engines have the firing order cast or stamped into the intake manifold.
  • LH and RH engines have a different firing order.
  • RH and LH engines have different camshafts.
  • Your need to know the engine rotation to set your ignition timing.
  • Left hand (LH) engines are standard rotation. Also known as Counterclockwise Rotation (CCR).
  • Chances are you have an LH standard rotation engine especially if it's a sterndrive or a single engine installation.

Warnings

  • Read your Owners Manual and shop manual
  • Read all safety precautions.
  • Remove all fuel vapors from bilge.
  • Work in a well ventilated area.
  • Have adequate lighting.
  • Wear safety glasses.
  • Keep clear of moving parts, belts and pulleys.
  • Damage, injury or death can result from fire or explosion of fuel or fuel vapors so use extreme caution whenever working on your engine.
  • Have a clean work area.
  • Have the correct tools.
  • Beware of sharp objects on your motor such as hose clamps as they can cut you.
  • Avoid getting fuel, oils or greases on your skin as some may be dangerous to your health.
  • Have a fire extinguisher close by.
  • Avoid sparks or open flames.
  • Have a partner close buy to assist in case of an emergency.

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Sources and Citations

Article Info

Categories: Boat Motors and Marine Engines

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