Sierra 18-3786

Every time you hit the water, your outboard's propeller relies on a single, critical component to stay secure: the prop nut. The Sierra 18-3786 prop nut, cross-referenced to Mercury MC#11-862907, steps in as a reliable aftermarket solution designed for boaters who demand durability without compromise. Crafted from high-grade stainless steel, this prop nut kit resists corrosion from saltwater exposure and the grind of freshwater use, ensuring your prop stays locked in place through rough wakes and high-speed runs.

Why This Prop Nut Stands Out for Marine Enthusiasts

Unlike basic hardware store fasteners, the Sierra 18-3786 is engineered specifically for marine propulsion systems. It includes a precision-machined nut, heavy-duty washer, and cotter pin, creating a complete assembly that handles the torque and vibration of outboard operation. Boaters often overlook prop nuts until a loose one causes vibration, spin-off drama, or worse—prop damage. This kit prevents those headaches, delivering peace of mind on every outing.

• Corrosion Resistance: 316 stainless steel construction thrives in harsh marine environments.
• Precision Fit: Matches OEM specifications for seamless installation on compatible Mercury propellers.
• Complete Kit: Nut, washer, and pin included—no hunting for extras.
• Cost-Effective Reliability: High-quality alternative that performs like factory parts at a fraction of the hassle.

Perfect Compatibility for Mercury Outboards

This prop nut fits a range of Mercury outboard models, particularly those with V6 and inline props from the 40hp to 125hp range. It's a direct replacement for MC#11-862907, commonly found on popular setups like the Mercury Black Max, Trophy Plus, and SpitFire props. Always double-check your propeller hub and shaft threading (typically 1-inch diameter) to confirm fitment, as variations exist across model years. Versatile enough for both recreational fishing boats and performance pontoons, it supports props with standard hub kits.

Step-by-Step Installation Guide

Swapping out a worn prop nut is a straightforward DIY job that takes under 30 minutes with basic tools. Here's how to do it right:

1. Tilt the outboard up and secure it. Disconnect the battery for safety.
2. Remove the old prop nut by straightening the cotter pin, pulling it out, and using a prop wrench to loosen counterclockwise.
3. Slide off the washer and inspect the prop shaft for damage or gear lube residue—clean thoroughly.
4. Reinstall the prop, slide on the new washer (tabs facing forward), then thread the Sierra 18-3786 nut by hand until snug.
5. Torque to manufacturer specs (around 50-60 ft-lbs for most Mercs—use a calibrated torque wrench), then insert and bend the cotter pin.
6. Lower the motor, reconnect the battery, and test spin the prop in neutral.

Pro Tip: Apply marine grease to the shaft before reassembly to ease future removals and protect against seizing.

Maintenance Tips to Maximize Longevity

To keep your Sierra prop nut performing season after season, inspect it during routine lower unit service. Look for wear on the washer tabs, nut threads, or pin—replace at the first sign of pitting or elongation. In saltwater, rinse with fresh water after every trip and apply anti-seize to threads annually. Vibration from unbalanced props accelerates wear, so balance-check your propeller yearly. Pairing this nut with a quality prop hub kit extends service life even further, reducing shear pin failures.

Real-World Performance Insights

Anglers and watersports fans rave about how this nut eliminates the dreaded "prop spin" during hard acceleration. One captain shared how it held firm through 500 hours of tournament fishing in the Gulf, outlasting two OEM nuts. Its beefier washer design better distributes load, minimizing hub slippage—a common killer on older Mercs. Whether you're chasing stripers or carving wakes, the Sierra 18-3786 delivers the grip you need for confident throttle response.