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3 Easy Steps for Prop and Lower Unit Care

Nov. 5 2025 Maintenance By Patrick Pershing

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Cope Marine Guide: 3 Easy Steps for Prop and Lower Unit Care

At Cope Marine, we know that your propeller and lower unit are what make your boat go. Neglect them, and you could find yourself stranded on the water. The good news? Proper prop and lower unit maintenance is simple, takes only a few minutes, and requires just a few basic tools. Follow our guide below to keep your boat running smoothly.

Step 1: Inspect the Propeller

The first step in prop and lower unit care is a careful inspection of the prop. Here’s what you need and how to do it:

Tools Needed:

  • Pliers (to remove the cotter pin)

  • 1 1/16″ deep socket with breaker bar (most common size) or what size your prop requires

  • Scrap piece of 2″ x 4″

Procedure:

  1. Remove the cotter pin from the prop nut.

  2. Wedge the 2×4 between the bottom of the anti-ventilation plate and a prop blade to prevent the prop from spinning.

  3. Use the socket and breaker bar to loosen the nut.

  4. Remove the nut and washers — tip: take a photo of the washer order with your phone and place them on a rag to ensure correct reassembly.

  5. Remove the prop hub and inspect it for dirt or damage. Clean with a rag to remove old grease.

  6. Inspect the prop shaft closely, paying attention to splines. Clean off old grease and contaminants.

  7. Check for fishing line wrapped around the prop shaft. This can get under the lower unit seal and damage it, allowing water into your gear case. Remove any fishing line carefully.

A clean, damage-free prop ensures smooth performance and prevents costly repairs down the line.

Step 2: Inspect the Lower Unit

Next, it’s time to inspect the lower unit and oil for potential issues.

Check for:

  • Leaking seals — a damaged seal must be replaced.

  • Water or metal shavings in the gear oil — this could indicate serious internal damage.

Procedure:

  1. Lower the motor as far as possible (without hitting the skeg on the ground).

  2. Locate the two drain screws: upper and lower. Remove the lower screw and let a few drops of oil drip into your hand. Replace the screw afterward.

  3. Inspect the oil’s color and check for metal shavings.

    • Milky oil = water has entered the gear case. Stop using the boat and get repairs immediately.

Regular lower unit inspections help prevent major gear damage and keep your boat safe on the water.

Step 3: Reassemble & Lubricate

Once everything is inspected and cleaned, it’s time to put everything back together.

Procedure:

  1. Grease the prop shaft using a manufacturer-recommended marine grease.

  2. Replace the prop hub and prop.

  3. Reinstall washers in the correct order and hand-tighten the nut.

  4. Wedge the 2×4 again between the prop blade and anti-ventilation plate. Torque the nut to the manufacturer’s specifications.

  5. Replace the cotter pin and bend the ends down to lock it in place.

And that’s it! Your prop and lower unit are ready for the water. Regular maintenance like this keeps your boat running efficiently and prevents costly repairs later.

Pro Tips from Cope Marine:

  • Always remove fishing line from the prop shaft — it’s the most common cause of seal damage.

  • Inspect your gear oil at least once a season or before long trips.

  • Taking a few photos during disassembly can save headaches when putting everything back together.

With just a few minutes of care, you can hit the water confidently, knowing your prop and lower unit are in top shape.