Sierra 18-8404-1

Upgrade Your Marine Engine Reliability with the Sierra Starter Bolt

Keeping your outboard motor running smoothly starts with the right hardware. The Sierra 18-8404-1 starter bolt delivers the sturdy hold you need for your Mercury engine's starter motor. Crafted from high-grade stainless steel, this bolt resists corrosion from saltwater exposure and harsh marine environments, ensuring long-term performance without the worry of loosening or stripping over time.

Boat owners know that a secure starter bolt prevents vibrations from compromising engine starts, especially during those high-RPM runs or choppy waters. Unlike generic hardware store fasteners, this OEM-spec replacement matches Mercury's engineering tolerances perfectly, restoring factory-level security to your setup.

Perfect Fit for Popular Mercury Outboards

Engineered as a direct cross-reference to Mercury part MC#10-8083434, the Sierra 18-8404-1 bolts right into a range of Mercury powerheads. It's commonly used on inline-four and V6 models from the 90s through early 2000s, including carbureted and EFI variants. Whether you're maintaining a classic 3.0L workhorse or a sporty 4.3L, this bolt ensures compatibility without modifications.

• Direct replacement for OEM starter mounting hardware
• Fits most Mercury Marine engines requiring 10-8083434 spec
• Ideal for repowers, rebuilds, or routine starter service

Pro tip: Always cross-check your engine's serial number against Mercury's parts catalog to confirm fitment, as slight variations exist across model years.

Key Features That Stand Out in Harsh Conditions

This isn't just any bolt—it's built for the marine world. With precise threading and a tensile strength that exceeds standard requirements, it handles the torque demands of starter motors up to 1.5 kW. The corrosion-resistant finish shrugs off electrolysis and galvanic action, a common killer for lesser parts in brackish or saltwater use.

Key specs include:

• Material: Marine-grade stainless steel
• Thread size: Matches OEM M8 or M10 (per Mercury spec)
• Length and pitch: Exact OEM dimensions for secure fit
• Packaged for easy storage and quick access

Sierra's rigorous testing mimics real-world boating stresses, from engine bay heat to constant submersion, giving you peace of mind on every outing.

Simple Installation for DIY Mechanics

Swapping out a worn starter bolt takes under 30 minutes with basic tools. Disconnect the battery, remove the old bolt using a deep socket and torque wrench, then thread in the new Sierra part. Aim for Mercury's recommended torque—typically 20-25 ft-lbs—to avoid over-tightening, which can gall threads or crack housings.

Common pitfalls to avoid:

1. Skipping anti-seize compound on threads for easier future removal
2. Not inspecting the starter mounting holes for wear or debris
3. Forgetting to bench-test the starter before reinstall

If you're dealing with a seized bolt, apply penetrating oil overnight and use a breaker bar. Fresh hardware like this Sierra bolt often resolves intermittent starting issues tied to loose mounts.

Why Boaters Trust Sierra Engine Parts

Sierra has earned its stripes as a go-to aftermarket brand by prioritizing quality over cost-cutting. Their parts undergo the same salt-spray and vibration tests as OEMs, often at a fraction of the dealer markup. For the Sierra 18-8404-1, that means reliable starts season after season, backed by a boating community's seal of approval.

Investing here means fewer trailered headaches and more time on the water. Pair it with routine starter solenoid checks and battery maintenance for bulletproof reliability.