How to Change an ACME Propeller: A Step-by-Step Guide for Boat Owners

Your propeller is one of the hardest-working components on your boat. Whether you’ve picked up damage from an unexpected underwater obstacle or you’re upgrading for better surf performance, knowing how to safely remove and install a new prop is an essential skill for any boat owner.

The good news? With the right tools and a little patience, changing a propeller is absolutely something you can handle yourself.

Let’s walk through it.

Before you get started, gather the following tools:

• Crescent wrench

• Pliers

• Gloves

• Prop puller

Pro Tip: Always keep a prop puller in your boat toolkit. It’s one of those tools you may not use often — but when you need it, you really need it.
]How to Remove Your Existing Propeller

Follow these steps carefully to protect both your prop and shaft.

1. Remove the Cotter Pin

Start by removing the cotter pin from the prop shaft using pliers.

2. Loosen the Prop Nut

Back the propeller nut off until there is roughly ¼ inch of space between the nut and the prop hub.

👉 Do not fully remove the nut yet. This protects the shaft when the prop breaks free.

3. Prepare the Prop Puller

Back out the puller bolt so the tool can slide easily into position.

4. Position the Puller

Insert the U-shaped end of the puller around the shaft and just aft of the strut. Using a wrench, tighten the puller bolt clockwise to apply pressure to the end of the shaft.

Important Tips:

• ❌ Do NOT overtighten

• ❌ Do NOT use an impact wrench

Both can damage the puller or propeller.

5. Break the Prop Free

Sometimes after using the puller the prop the propeller is still secured tightley and has not moved. Using a rubber mallet you can tap the U-shaped portion opposite the bolt 2–3 times. This shock typically releases the prop from the shaft taper.

Repeat if necessary.

6. Remove the Nut

Once the prop is loose, remove the lock nut while holding the prop securely.

7. Remove the Key

Before sliding the prop off:

• Rotate the shaft so the key faces upward

• Remove the key

Note: This step does not apply to spline propellers.

Installing Your New ACME Propeller

A proper installation ensures peak performance and prevents vibration or drivetrain damage.

1. Test the Fit

Place the new prop on the shaft without the key to confirm where it fully seats on the taper.

Remove it once verified.

2. Install the Key

Insert the key into the prop shaft.

👉 Improper placement can cause the key to jam and prevent the prop from seating fully.

(Not applicable for spline props.)

3. Slide the Prop Onto the Shaft

Install the prop onto the taper. It should feel snug — not forced.

4. Tighten the Prop Nut

Install the nut firmly against the hub.

DO NOT exceed 50 ft-lbs of torque.

Over-torquing can damage both the prop and shaft.

5. Install the Cotter Pin

Insert the cotter pin and bend the ends back using pliers to secure it.

6. Re-Torque After Use

After 5–10 hours on the water, re-tighten the prop nut. Forces from acceleration and deceleration can cause it to settle slightly.

This is a step many boat owners forget — don’t skip it.