Determine Your Mercruiser Engine Rotation

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

Steps

Locate your engine serial number.
Contact an online help-site such as sterndrive-information.com to get your engine rotation.
Look for original factory specification decals which might designate the engine rotation.
Observe the rotation of the engine cranking or running if possible.

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.
Your need to know the engine rotation to set your ignition timing.
RH and LH engines have different camshafts.
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.

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